“Let food be thy medicine, and medicine be thy food.”

-Hippocrates, referred to as the “Father of  Modern Medicine”

Life depends on nourishment and the quality of life depends greatly on the foods you choose to eat. Any discussion of nutrition must begin with an understanding of nutrition, nutrients, and their overall relationship to health and well-being.

1.1 Defining Nutrition, Health, and Disease

The word nutrition first appeared in 1551 and comes from the Latin word nutrire, meaning “to nourish.” Today, we define nutrition as the sum of all processes involved in how organisms obtain nutrients, metabolize them, and use them to support all of life’s processes. Nutritional science is the investigation of how an organism is nourished, and incorporates the study of how nourishment affects personal health, population health, and planetary health. Nutritional science covers a wide spectrum of disciplines. As a result, nutritional scientists can specialize in particular aspects of nutrition such as biology, physiology, immunology, biochemistry, education, psychology, sustainability, and sociology.

Without adequate nutrition the human body does not function optimally, and severe nutritional inadequacy can lead to disease and even death. The typical American diet contains adequate calories, but is lacking in many ways, from not containing the proper amounts of essential nutrients, to being too speedily consumed, to being only meagerly satisfying.

Registered Dietitians (RD), also called Registered Dietitian Nutritionists (RDN), are nutrition professionals who integrate their knowledge of nutritional science into helping people achieve a healthy diet and develop good dietary habits. Through their knowledge and experiences, RDs/RDNs specialize in translating nutrition science into practical advice. Becoming an RD/RDN requires a college degree with an emphasis in chemistry, anatomy and physiology, and other sciences, the completion of a 1200-hour dietetic internship in clinical and community settings, and passing the national certification exam. Once you achieve RD/RDN status, you must complete 75-hours of continuing education in nutrition every five years. RDs/RDNs work in many diverse settings including hospitals, clinics, long-term care facilities, schools, health clubs, grocery stores, private practice, insurance companies, and corporate wellness programs. They can help you overcome disordered eating, set realistic weight loss and weight management goals, manage chronic diseases, or help you achieve optimal athletic performance. The Academy of Nutrition and Dietetics (AND) is the largest organization of nutrition professionals in the world and dietitians registered with the AND are committed to helping Americans eat well and live healthier lives. To learn more about the AND and their nutritional advice for consumers, visit eatright.org.

Nutrition and Health and Disease

Your ability to wake up, to think clearly, to communicate, to hope, to dream, to go to school, to gain knowledge, to go to work, to earn a living, and to do all of the things that you like to do are dependent upon one factor—your health. Good health means you are able to function normally and work hard to achieve your goals in life. In 1946, the World Health Organization (WHO) defined health as “a state of complete physical, mental, and social well-being, and not merely the absence of disease or infirmity.”¹ This definition was adopted into the WHO constitution in 1948 and remains to this day. A triangle is often used to depict the equal influences of physical, mental, and social well-being on health.

Disease is defined as any abnormal condition affecting the health of organisms and typically characterized by specific signs and symptoms. Diseases are broadly categorized as resulting from pathogens (i.e., bacteria, viruses, fungi, and parasites), deficiencies, genetics, and/or physiological dysfunction. Diseases that primarily affect physical health are those that impair body structure (as is the case with osteoporosis), or functioning (as is the case with cardiovascular disease). Mental illnesses primarily affect mental and social well-being.

The foods we eat affect multiple aspects of our health. For example, a teen with type 2 diabetes (a disease often brought on by poor diet and lack of physical activity) is first diagnosed by physical signs and symptoms such as increased urination, excessive thirstiness, and unexplained weight loss. But research has also found that teens with uncontrolled type 2 diabetes often have impaired thinking and may not interact well with others in school, thereby affecting mental and social well-being. This is just one example of a physiological disease that can affect physical, mental, and social aspects of health.

In the early twentieth century, most nutrition-related diseases and conditions were related to inadequate calorie consumption or deficiency of nutrients. In the latter part of the twentieth century nutrition scientists, public health organizations, and the American public increasingly recognized that eating too much of certain foods is linked to chronic diseases. Table 1.1.1 shows the top ten causes of death in the US. As you can see, many of these causes are related to nutrition. We now know that diet-related conditions and diseases include but are not limited to cardiovascular (heart) diseases including hypertension (high blood pressure) and stroke, obesity, type 2 diabetes, several forms of cancer, and osteoporosis.

Table 1.1.1 United States Leading Causes of Death 2017 & 2018 in deaths per 100,000 US Standard Population²

1.2  Assessing Your Health

There are many factors that determine whether you are “healthy.” Although the WHO definition describes health as not just the absence of disease, but also encompassing psychological, emotional, and social well-being, most of Western medicine is focused on a person’s physical health. As we have discussed previously, and will continue to discuss throughout this course, nutrition plays an enormous role in determining our overall health. Assessing one’s nutritional status can help us determine whether nutritional intake (or lack of) is affecting the development or continuance of nutrition-related health conditions. No one eats 100% healthy foods 100% of the time, but with assessment we look at the overall eating pattern and how it affects overall health. Nutrition assessment uses many tools to help determine whether a person is well-nourished or malnourished (referring to either undernourished or overnourished).

There are six areas to consider when assessing health through a nutrition lens. An easy way to remember these areas is using the letters ABCDEF:

A:  anthropometric

B:  biochemical

C:  clinical

D:  dietary

E:  environmental

F:  family history

A: Anthropometric Assessment

The word anthropometric comes from two terms: anthropo meaning “human” and metric meaning “measure.” There are many different measures used to assess growth in humans including height, weight, body mass index (BMI), head circumference, girth measurements of limbs, waist, hip, and body composition measures such as skinfold/fat fold thickness or bioelectrical impedance analysis. We then compare those measures to known health standards. Often these types of measurements are used to assess the growth of children and adolescents. Some of these measures such as height and weight are used throughout our lifetimes, comparing measurements over time, or comparing one person to another. We will discuss these measures in more detail in Chapter 9 Energy Balance, Chapter 12 Nutrition and Fitness, and Chapter 18 Nutrition Through the Lifecycle.

B: Biochemical Assessment

Biochemical assessment includes laboratory tests that can measure a nutrient or its metabolites in the blood, urine, feces, or other bodily secretions. We can learn quite a bit about a person’s health by looking at these tests and they are routinely collected and examined as part of a general physical by your doctor. In nutrition, for example, we look at the levels of glucose in the blood and in the urine to determine if a person has or is at risk for diabetes. We look at blood cholesterol profiles to help determine risk for some forms of cardiovascular disease. The amount of iron in the blood can indicate a person’s risk for anemia. It is recommended that patients keep copies of routine lab tests to examine trends over time.

C: Clinical Assessment

In addition to anthropometric and biochemical measures, clinical signs and symptoms are used to assess nutritional status such as a potential nutrient deficiency or toxicity. Signs are those things that can be easily seen such as bleeding, vomiting, or fainting. Symptoms are those things that a patient may be experiencing that cannot easily be seen and must be described such as a headache, nausea, dizziness, or pain. Special attention is given to a person’s organs such as skin, eyes, tongue, ears, mouth, hair, nails, and gums. Clinical methods of assessing nutritional status involve checking signs at specific points on the body, or asking patients about any symptoms that may indicate a nutrient deficiency. Often other clinical measures such as temperature and blood pressure are also taken.

If a nutrient deficiency is suspected based on signs or symptoms, often a biochemical test is completed to help identify the exact nutrient that may be inadequate or missing. There are two types of nutrient deficiencies a person may develop. A primary nutrient deficiency occurs when a person does not consume enough of an essential nutrient. A secondary nutrient deficiency occurs when enough of the nutrient is consumed, but for some reason the body is unable to use that nutrient effectively. Secondary nutrient deficiencies can occur because of functional problems in the digestive tract, medications that may be interfering with the body’s absorption or metabolism of a particular nutrient, the body’s natural aging process, and many other reasons.

D: Dietary Assessment

Dietary methods of assessment include looking at past and current intake of nutrients from food by individuals or a group to help determine their nutritional status. Completing a dietary assessment is crucial when trying to determine whether or not your intake is related to a disease or condition. There are several methods that may be used to do this:

• 24-hour dietary recall. A trained professional asks a person to recall all food or drink consumed in the previous 24-hours. This is a quick and easy method. However, it is dependent upon the person’s short-term memory and may not be very accurate. It also looks at just one day, which may not be a “typical” day of intake for the individual.
• Food Frequency Questionnaire. The person is given a list of foods and asked to indicate average intake per day, per week, and per month. This method is inexpensive and easy to administer, however it often lacks detail and may not be very accurate. It can still provide a broad overview of one’s overall eating pattern.
• Food Diary. Food intake is recorded at the time of eating. This is also known as a food journal or food record. These diaries can be done with paper and pencil, but are more likely to be recorded using apps on a phone or other electronic device. This method is generally reliable but is difficult to accurately maintain for more than a few days, and portion sizes can be difficult to estimate.
• Observed Food Consumption. This method requires food to be weighed and the nutrient content exactly calculated. It is very accurate, but time consuming and expensive, and is usually done only for research purposes.

E: Environmental Assessment (Lifestyle)

Where and how you live can have a profound effect on your health and nutritional status. Many environmental factors play a role including your living situation (alone, with a family, with friends, etc.), geographic location (urban vs rural, north vs south, etc.), socioeconomic position, access to healthy foods, your ability to prepare food, and other lifestyle factors such as exercise and sleep patterns, emotional health, and work-life balance.

An assessment of your environment includes evaluating not only your nutrition, but also your personal habits. Many diseases are preventable by simply staying away from certain behaviors (smoking, excessive alcohol use, risky sexual activity, etc.). Instead adopt healthful measures like participating in regular physical activity, wearing seat belts in the car and helmets while cycling, and finding healthy ways to minimize your response to stressors like meditation or spending time outdoors. As stated earlier, health is more than just physical. Emotional health is often hard to talk about; however, a person’s quality of life is highly affected by emotional stability. Finding balance between work and life is a difficult and continuous process involving keeping track of your time, taking advantage of job flexibility options, saying no, and finding support when you need it. Work-life balance can influence what you eat too.

F: Family Medical History

Everyone starts out in life with the genes handed down to them from their mother and father. Genes are responsible for your many traits as an individual and are defined as the sequences of DNA that code for all the proteins in your body. The expression of different genes can determine the color of your hair, skin, and eyes, and even if you are more likely to be fat or thin and if you have an increased risk for a certain disease. The sequence of DNA that makes up your genes and determines your genetic makeup is called your genome. In 2003, the Human Genome Project was completed and now the entire sequence of DNA in humans is known. It consists of about three billion individual units and contains between 25,000 and 30,000 genes. The human genome that was sequenced was taken from a small population of donors and is used as a reference DNA sequence for the entire population. Each of us has a similar but unique DNA sequence. Only identical twins and cloned animals have the exact same DNA sequence.

Epigenetics is the study of how your behaviors and your environment may turn genes “on” or “off,” causing changes that can affect how your genes work. In recent years scientists have been studying the possible epigenetic links between genes and nutrients. Initial studies looked at nutrigenomics, the study of the intake of nutrients and their effects on genetic expression in an individual. Not all epigenetic changes are permanent. A beneficial change in nutrient intake, increased physical activity, or quitting smoking can reverse some epigenetic modifications and improve health.

A second way to look at the interplay between nutrients and genes is to identify genetic markers in individuals that may modify their need for or use of various nutrients which may influence health outcomes. This is called nutrigenetics. Genetic differences may help explain why some people achieve weight loss with certain diets and others do not. Or whether a person may benefit more from a low sodium diet than someone else might. You may see internet sites touting personalized nutrition, their ability to help you (for a hefty fee), “eat right for your genes.” Although this is an exciting area of research, the science is complicated. Be sure that if you access these services, that there is a health professional such as an RD/RDN who can help you interpret your individual results.

Because genetics play a large role in defining your health it is a good idea to learn whether there are some diseases and conditions that may be more likely to affect you based on your inherited genes. To do this, record your family’s medical history. Start by drawing a chart that lists your immediate family and relatives. The next time you attend a family event or see extended family members, start filling in the blanks. What did people die from? What country did Grandpa come from? While this may be an interesting project historically, it can also provide you with a practical tool to determine to what diseases you might be more susceptible. This will allow you to make better dietary and lifestyle changes early on to help prevent a disease from being handed down from your family to you. It is good to compile your information from multiple relatives.

Risk Factors

Assessing your current health status based on these six categories can help you identify some of your risk factors. A risk factor is something that makes you more likely to develop adverse health conditions. Some risk factors are inherited through your genes as discussed previously. These risk factors are part of your DNA, but may be affected by your health behaviors, either positively or negatively. However, scientists consider them non-modifiable because they are part of your genetic code which cannot be altered. Other risk factors such as biological sex, age, and race are also non-modifiable. Some risk factors are modifiable because they are choices an individual makes each day. For example, if you smoke you are more likely to develop lung cancer than someone who does not smoke. Thus smoking is a risk factor for lung cancer. Some people can smoke for years and never develop lung cancer, while others may develop lung cancer and never smoke. However, the chances that you will develop lung cancer if you’re a smoker are much higher than if you never smoked. If you quit smoking, you may reduce your risk of developing this terrible disease. Obesity, physical inactivity, and dietary factors such as low fiber intake and high saturated fat intake are risk factors for many different health conditions including heart disease, type 2 diabetes, and some forms of cancer. Choosing healthier meals and exercising regularly can go a long way to reducing the chances that you will develop one of these debilitating health conditions. The more risk factors you have for a health condition the more likely you are to eventually suffer from it. Assessing your health using ABCDEF allows you to identify your current risk factors and to take steps to modify those you can.

1.3  Nutrients

As we saw in the previous section, many different factors affect our overall health and well-being. In this course our primary focus is on the role of dietary nutrient intake and nutrient functions in body processes.

Our bodies require dozens of different chemicals found in food to help us maintain optimal health. These chemicals are called nutrients , and the study of how these chemicals interact with each other and with our bodies is called nutrition. Nutrients are substances required by the body to perform its basic functions. We consume our favorite foods and beverages (and sometimes our not so favorites) in an attempt to gain all of the necessary nutrients to achieve or maintain our health. Sometimes we also consume supplements in addition to foods to be sure we are getting all of the required nutrients.

Although all nutrients are important, scientists categorize some as essential. The word essential means we have to have it, however, in nutrition the word essential also means we have to obtain it from an outside source, from foods or beverages. In other words, an essential nutrient is one we need that we have to consume. Non-essential nutrients are also necessary and vital for good health, but these nutrients can be made by the body in sufficient amounts as long as adequate essential nutrients are consumed, and don’t necessarily need to be a part of our daily dietary intake. Sometimes a formerly non-essential nutrient may become conditionally essential. This means that under normal circumstances a person could manufacture what they need, but if, for example, they are taking a certain medication or have a medical condition that modifies their ability to make the nutrient, then they must consume it.

Nutrients are used to help us produce energy, detect and respond to environmental surroundings, move, excrete wastes, respire (breathe), grow, and reproduce. To make it easier to study nutrients, we combine those that have similar properties or functions into groups or “classes.” There are six classes of nutrients required for the body to function and maintain overall health. These classes are carbohydrates, protein, lipids, water, vitamins, and minerals.

Table 1.3.1  Classes of Nutrients and their Basic Functions

Macronutrients

Nutrients that are needed in large amounts are called macronutrients. There are four classes of macronutrients: carbohydrates, protein, lipids, and water. Of these macronutrients, three (carbohydrate, protein, and lipids) can be metabolically processed into cellular energy and thus are called energy nutrients. The energy from macronutrients comes from their chemical bonds. This chemical energy is converted into cellular energy in the form of adenosine triphosphate (ATP) that is then utilized to perform work, allowing our bodies to conduct their basic functions. Water is also a macronutrient in the sense that you require a large amount of it, but unlike the other macronutrients it does not yield calories.

A unit of measurement of food energy is the calorie (denoted with a small “c”). A calorie is the amount of energy required to raise 1 gram of water 1° Celsius. On nutrition food labels and in the field of nutrition the amount given for “Calories” is actually equivalent to each calorie multiplied by one thousand. A kilocalorie or kcal (one thousand calories, denoted with a small “c”) is synonymous with the “Calorie” (denoted with a capital “C”). When you see Calories on nutrition food labels it is equal to kcals (Calorie = kcal). Therefore, you can use “kcal” to denote amounts of energy from food (as we have done throughout this text). 

Carbohydrates

Carbohydrates are molecules composed of carbon, hydrogen, and oxygen. Any molecule that contains carbon atoms is considered an organic molecule. This use of the term organic refers only to the molecule’s chemical composition and is different from the use of the term organic in relation to how foods are grown. The main function of carbohydrates is to provide energy. The major food sources of carbohydrates are grains, milk, fruits, and starchy vegetables like potatoes. Non-starchy vegetables like broccoli or kale also contain carbohydrates, but in lesser quantities. Carbohydrates are almost exclusively found in plant-based foods. Carbohydrates are broadly classified into two forms based on their chemical structure: simple and complex.

One gram (g) of carbohydrates yields 4 kcal of energy for the cells in the body to perform work. In addition to providing energy and serving as building blocks for bigger macromolecules, carbohydrates are essential for proper functioning of the nervous system, heart, and kidneys.

All carbohydrates are made up of building blocks called monosaccharides, the most common monosaccharide is glucose. Some carbohydrates such as table sugar or honey are made of just two monosaccharides, so are called simple carbohydrates. Other carbohydrates are made up of hundreds or thousands of monosaccharides, and are called complex. Glucose can be stored for future use. In animals including humans, the storage molecule of carbohydrates is called glycogen and in plants it is known as starch. Glycogen and starches are complex carbohydrates, as is dietary fiber.

Proteins

Proteins are organic molecules composed of chains of amino acids. Amino acids are simple sub-units composed of carbon, oxygen, hydrogen, and nitrogen. The food sources of proteins are meats, dairy products, seafood, and a variety of different plant-based foods, most notably soy. The word protein comes from a Greek word meaning “of primary importance,” which is an apt description of these macronutrients; they are also known colloquially as the “workhorses” of life. Proteins provide 4 kcal of energy per g; however providing energy is not protein’s most important function. Proteins provide structure to bones, muscles and skin, they make up hormones, enzymes, neurotransmitters, and molecules important in immunity, and play a role in conducting most of the chemical reactions that take place in the body. Scientists estimate that greater than 20,000 different proteins exist within the human body.

Lipids

Lipids are also a family of organic molecules composed of carbon, hydrogen, and oxygen, but unlike carbohydrates, they are insoluble in water. Lipids are found predominantly in butter, oils, meats, dairy products, nuts, and seeds, and in many processed foods. The three main types of lipids are triglycerides (or triacylglycerols), phospholipids, and sterols. The main job of lipids is to store energy. Lipids provide more energy per g than carbohydrates or protein (9 kcal per g of lipids versus 4 kcal per g of carbohydrates/protein). In addition to energy storage, lipids serve as components of cell membranes, surround and protect organs, aid in temperature regulation, and regulate many other functions in the body.

Water

There is one other nutrient that we must consume in large quantities: water. Water does not contain carbon, making it an inorganic molecule. It is composed of two hydrogen (H₂) and one oxygen (O) per one molecule of water. More than 60% of your total body weight is water. Without it, nothing could be transported in or out of the body, chemical reactions would not occur, organs would not be cushioned, and body temperature would fluctuate widely. On average, an adult consumes just over two liters of water per day from food and drink. According to the “rule of threes,” a generalization supported by survival experts, a person can survive three minutes without oxygen, three days without water, and three weeks without food. Since water is so critical for life’s basic processes, the amount of water input and output is supremely important. However, water does not provide any kcal. So it is considered a macronutrient, but not an energy nutrient.

Micronutrients

Micronutrients are nutrients required by the body in very small amounts, but are still essential for carrying out bodily functions. Micronutrients include all the essential minerals and vitamins. There are 13 essential vitamins and 16 minerals (see Table 1.3.2 and Table 1.3.3 for a complete list and their major functions). In contrast to carbohydrates, protein, and lipids, micronutrients are not directly used for making energy and do not contain kcal, but they assist in the process of energy production as part of enzymes (i.e., coenzymes). Enzymes are proteins that catalyze chemical reactions in the body and are involved in all aspects of body functions from producing energy, to digesting nutrients, to building macromolecules. Micronutrients play many roles in the body.

Vitamins

The 13 vitamins are categorized as either water-soluble or fat-soluble. The water-soluble vitamins are vitamin C and all the B vitamins, which include thiamin, riboflavin, niacin, pantothenic acid, B₆, biotin, folate and B₁₂. The fat-soluble vitamins are A, D, E, and K. Vitamins are required to perform many functions in the body such as making red blood cells, synthesizing bone tissue, and playing a role in normal vision, nervous system function, and immune system function.

Vitamin deficiencies can cause severe health problems. For example, a deficiency in niacin causes a disease called pellagra, which was common in the early twentieth century in some parts of America. The common signs and symptoms of pellagra are known as the “4D’s—diarrhea, dermatitis, dementia, and death.” Until scientists found out that better diets relieved the signs and symptoms of pellagra, many people with the disease ended up in asylums awaiting death. The deficiency of other vitamins was found to cause other disorders and diseases such as scurvy (vitamin C), night blindness (vitamin A), and rickets (vitamin D).

Table 1.3.2 Vitamins and Their Major Functions

Minerals

Minerals are solid inorganic substances that form crystals and are classified depending on how much of them we need. Trace (minor) minerals such as molybdenum, selenium, zinc, iron, and iodine, are only required in a few milligrams (mg) or less per day while major minerals such as calcium, magnesium, potassium, sodium, and phosphorus, are required in hundreds of mg. Like vitamins, minerals do not contain kcal. Many minerals are critical for enzyme function, others are used to maintain fluid balance, build bone tissue, synthesize hormones, transmit nerve impulses, contract and relax muscles, and protect against harmful free radicals.

Table 1.3.3 Minerals and Their Major Functions

To review, the dozens of nutrients that the body requires are grouped into six classes based on form and function. Below is a summary of the characteristics of the six nutrient classes.

Table 1.3.4  Summary of Nutrient Class Characteristics

Food Energy

As discussed previously, food energy is measured in Calories and commonly referred to as kcal. Though this is only the first chapter, you have already seen the words “kcal” and “energy” used several times. In everyday life you have probably heard people talk about how many kcal they burned on the treadmill or how many calories are listed on a bag of chips. Kcal are a measure of energy. It takes quite a lot of kcal to keep us alive. Even if a person is in a coma, they still burn approximately 1000 kcal of energy in order for their heart to beat, their blood to circulate, their lungs to breathe, etc. We burn even more kcal when we exercise. A food’s kcal are determined by putting the food into a bomb calorimeter, heating it, and determining the energy output (energy = heat produced). The carbohydrates, proteins, and fats we eat and drink provide kcal for us (and alcohol as well if we choose to consume it).

Food Quality

One measurement of food quality is the amount of nutrients it contains relative to the amount of energy it provides. High quality foods are nutrient dense, meaning they contain many nutrients relative to the amount of calories they provide. A food with high nutrient density would have a large amount of various beneficial nutrients in each “bite” of that particular food. Because “bites” are different for everyone, we use common measures such as gram (g), ounce (oz), cup (c), pound (lb), liter (L), tablespoon (tbs), etc. to help us compare different foods. (See common measures used in Appendix 1). Determining nutrient density of a food is not straightforward. One must consider the nutrient profile of a food as a whole, and it can be quite subjective. However, it is generally agreed that whole fruits and vegetables, 100% whole grains, nuts, and legumes tend to have high nutrient density. Food quality is additionally associated with its taste, texture, appearance, microbial content, and how much consumers like it.

Another measure of food quality is to examine the number of kcals in a food relative to the size of each “bite.” The term used to describe this is energy density or calorie density. Foods high in fats and sugars, like fast food burgers, pizza, candy bars, etc. would be considered energy dense since they provide many calories per bite but are typically lacking several essential vitamins, minerals, and other beneficial nutrients like fiber. We can compare the energy density of different foods if we know the number of kcals and the size of a serving for each.

A third term often used to describe food quality is “empty calorie.” Foods such as carbonated sugary soft drinks provide many calories, but very few, if any, beneficial nutrients, making the calories “empty.”

We can compare meals to examine food quality:

Let’s say we have a choice between two different breakfasts depicted in Figures 1.3.5 and 1.3.6. Each breakfast contains 500 kcal. But breakfast #2 provides many more nutrients in those 500 kcal than do the donuts. There are several different vitamins and minerals in the two types of berries and in the spinach. These fruits and vegetable also contain fiber, and there is lean protein in the eggs.

The donuts in breakfast #1 contain 500 kcal as well, but those kcals are primarily fat and sugar. There are very few vitamins or minerals in the donuts, and almost no fiber or protein. Therefore, breakfast #2 is more nutrient dense.

We can also compare the energy density of the two breakfasts. Because we know the weights of the two (in grams) and that both contain 500 kcal, we can calculate the energy density of each breakfast.

Energy density of breakfast #1: 500 kcal/135 g = 3.7 kcal per gram of food

Energy density of breakfast #2: 500 kcal/350 g = 1.4 kcal per gram of food

Breakfast #1 has more than 2.5 times as many kcal per gram of food than breakfast #2. Therefore breakfast #1 has higher energy density.

1.4 Nutrition Research and the Scientific Method

Similar to the method by which a police detective finally charges a criminal with a crime, nutritional scientists discover the health effects of food and its nutrients by first making an observation. Once observations are made, they come up with a hypothesis, test their hypothesis, and then interpret the results. After this, they gather additional evidence from multiple sources and finally come up with a conclusion on whether the food suspect fits the claim. This organized process of inquiry developed in the 17th century is used in the sciences including nutritional science, and is called the scientific method.

One example of how the scientific method has been used in nutritional sciences is in the identification of the mineral iodine and it’s role in the thyroid gland. In the early 1800s the development of an enlargement of the neck, known as a goiter, was common in the population, especially in those living far from the sea. It was thought to be caused by poor hygiene. Because of the use of the scientific method, we now know that a goiter develops when iodine in the diet is deficient. Below is a description of how this was determined.

In 1811, French chemist Bernard Courtois was isolating saltpeter for producing gunpowder to be used by Napoleon’s army. To carry out this isolation he burned some seaweed and, in the process, observed an intense violet vapor that crystallized when he exposed it to a cold surface. He sent the violet crystals to an expert on gases, Joseph Gay-Lussac, who identified the crystal as a new element. It was named iodine, the Greek word for violet. The following scientific record is some of what took place in order to conclude that iodine is a nutrient using the steps of the scientific method: observation, hypothesis, experimental test, interpretation of results.⁵ Share your results with other scientists. Repeat these steps to gather more evidence until you have enough evidence to reach a conclusion.

Steps of the Scientific Method used to identify Iodine

Observation. Eating seaweed is a cure for goiter, an enlargement of the thyroid gland in the neck.

 

Hypothesis. In 1813, Swiss physician Jean-Francois Coindet hypothesized that the seaweed contains iodine and he could use just iodine instead of seaweed to treat his patients.

Experimental test. Coindet administered iodine tincture orally to his patients with goiter.

Interpret results. Coindet’s iodine treatment was successful.

Gathering more evidence. Many other physicians contributed to the research on iodine deficiency and goiter.

Hypothesis. French chemist Chatin proposed that the low iodine content in food and water of certain areas far away from the ocean were the primary cause of goiter and renounced the theory that goiter was the result of poor hygiene.

Experimental test. In the late 1860s the program, “The stamping-out of goiter,” started with people in several villages in France being given iodine tablets.

Results. The program was effective and 80% of children with goiter were cured.

Hypothesis. In 1918, Swiss doctor Bayard proposed iodizing salt as a good way to treat areas where much of the population suffered from goiter.

Experimental test. Iodized salt was transported by mules to a small village at the base of the Matterhorn where more than 75% of school children had goiter. It was given to families to use for six months.

Results. The iodized salt was beneficial in treating goiter in this remote population.

Experimental test. Physician David Marine conducted the first experiment of treating goiter with iodized salt in America in Akron, Ohio.⁶

Results. This study conducted on over 4,000 school children found that iodized salt prevents goiter.

Conclusions. Seven other studies similar to Marine’s were conducted in Italy and Switzerland that also demonstrated the effectiveness of iodized salt in treating goiter. In 1924, US public health officials initiated the program of iodizing salt and started eliminating the scourge of goiterism. Today more than 70% of American households use iodized salt and many other countries have followed the same public health strategy to reduce the health consequences of iodine deficiency.

This is just one example of how the scientific method was used to determine how to treat a specific health condition. There have been millions of studies using this method, and you are benefitting from the results of these studies when you take a medication for a specific disease or condition, or when you modify a behavior to achieve a desired result.

Evidence-Based Approach to Nutrition

It took more than 100 years from iodine’s discovery as an effective treatment for goiter until public health programs recognized it as such. Although a lengthy process, the scientific method is a productive way to define essential nutrients and determine their ability to promote health and prevent disease. The scientific method is part of the overall evidence-based approach to designing nutritional guidelines. An evidence-based approach to nutrition includes⁷:

• Defining the problem or uncertainty (e.g., the rate of colon cancer is higher in people who eat red meat)
• Formulating it as a question (e.g., does eating red meat contribute to colon cancer?)
• Setting criteria for quality evidence
• Evaluating the body of evidence
• Summarizing the body of evidence and making decisions
• Specifying the strength of the supporting evidence required to make decisions
• Disseminating the findings

The Food and Nutrition Board of the National Academy of Medicine (NAM) [formerly known as  the Institute of Medicine (IOM)], a non-profit, non-governmental organization, constructs its nutrient recommendations (i.e., Dietary Reference Intakes, or DRI) using an evidence-based approach to nutrition. The entire procedure for setting the DRI is documented and made available to the public. The same approach is used by the US Department of Agriculture (USDA) and US Department of Health and Human Services (HHS). The USDA and HHS websites are great tools for discovering ways to optimize health; however, it is important to gather nutrition information from multiple resources as there are often differences in opinion among various scientists and public health organizations.

Types of Scientific Studies

There are many types of scientific studies that can be used to test a particular hypothesis including epidemiological studies, interventional clinical trials, and randomized clinical interventional trials.

Table 1.4.1  Types of Scientific Studies

Epidemiological studies observe what is actually happening in a population in relation to health over time. The goal is to find factors associated with an increased or decreased risk for a health event, though these sometimes remain elusive. Often these types of studies can help refine a hypothesis. They can be used to predict future health needs, but cannot directly determine if one variable causes another.

Interventional clinical trial studies are scientific investigations in which a variable is changed between groups of people. When well done, this type of study allows one to determine causal relationships. A randomized clinical interventional trial is a study in which participants are assigned by chance to separate groups that compare different treatments. Neither the researchers nor the participants can choose or know which group a participant is assigned to. That’s called a “double blind” study. In these types of studies, the control group usually receives a placebo instead of the actual intervention. These are powerful tools to provide supporting evidence for a particular relationship and are considered the “gold standard” of scientific studies.

The attributes of high quality clinical interventional trial studies are:

• those that include a control group, which does not receive the intervention, to which you can compare the people who receive the intervention being tested.
• those in which the subjects are randomized into groups, meaning a given subject has an equal chance of ending up in either the control group or the intervention group. This is done to ensure that any possible confounding variables are likely to be evenly distributed between the control and the intervention groups.
• “double-blinded” studies in which neither the researchers nor the participants know into which group they have been assigned. This is done to reduce bias on the part of the researchers.
• those studies that include a sufficient number of participants (signified by “n”). Generally the higher the “n” the more robust and significant is the study.

The limitations of clinical intervention studies are that they are difficult to carry on for long periods of time, are costly, and require that participants remain compliant with the intervention. Furthermore, it is unethical to study certain interventions. (An example of an unethical intervention would be to advise one group of pregnant mothers to drink alcohol to determine the effects of alcohol intake on pregnancy outcome, because we know that alcohol consumption during pregnancy damages the developing fetus.)

Because of the types of study limitations it is clear that epidemiological studies complement interventional clinical trial studies and BOTH are necessary to construct strong foundations of scientific evidence for health promotion and disease prevention.

Other scientific studies used to provide supporting evidence for a hypothesis include laboratory studies conducted on animals or cells. An advantage of this type of study is that they typically are less expensive than human studies and they require less time to conduct. Other advantages are that researchers have more control over the environment and the amount of confounding variables can be significantly reduced. Moreover, animal and cell studies provide a way to study relationships at the molecular level and are also helpful in determining the exact mechanism by which a specific nutrient causes a change in health. The main disadvantage of these types of studies is that researchers are not working with whole humans and thus the results may not be as applicable. Nevertheless, well-conducted animal and cell studies that can be repeated by multiple researchers and obtain the same conclusion are definitely helpful in building the evidence to support a scientific hypothesis.

Science is always moving forward, often slowly. One study is not enough to make a guideline or a recommendation or cure a disease. Science is a step-by-step, gradual process that builds on past evidence and finally culminates into a well accepted conclusion. Unfortunately, not all scientific conclusions are developed in the interest of human health and it is important to know where a scientific study was conducted and who provided the funding for the study. This can help you identify bias. Bias means that a researcher or group prefers one outcome over another, so they do not give all possible outcomes an equal chance. If you read an air quality study paid for by a tobacco company that found that smoking did not reduce indoor air quality, you would be skeptical of that result. You should also be skeptical of one on the benefits of red meat performed at a laboratory funded by a national beef association, or the benefits of a dietary supplement paid for by a supplement manufacturing corporation.

Science can also be contentious even among experts that do not have any conflicting financial interests. Contentious science is actually a good thing as it forces researchers to be of high integrity, well-educated, well-trained, and dedicated. It also instigates public health policy makers to seek out multiple sources of evidence in order to support a new policy. Agreement involving many experts across multiple scientific disciplines is necessary for recommending dietary changes to improve health and prevent disease. Although a somewhat slow process, it is better for our health to allow the evidence to accumulate before incorporating some change in our diet.

1.5  Nutrition and the Media

A motivational speaker once said, “A smart person believes half of what they read. An intelligent person knows which half to believe.” In this age of information where instant Internet access is just a click away, it is easy to be misled if you do not know where to go for reliable nutrition information. There are a few websites that can be consistently relied upon for accurate material that is updated regularly.

Using Eyes of Discernment

“New study shows that margarine contributes to arterial plaque.”

“Asian study reveals that two cups of coffee per day can have detrimental effects on the nervous system.”

“Stack your snacks to add three pounds of muscle.”

How do you react when you read news of this nature? Do you boycott margarine and coffee? Change your snacking habits? Nutrition-related hyperbolic headlines and advertisements have been around for decades. In the 1930s there were ads recommending a “reducing soap” that would wash away fat and years of age. In the 1950s and 60s you could reduce your weight by listening to certain music, or by rubbing an “electric spot reducer” over your abdomen. We still see similar types of advertisements on food packaging, and in print and social media. Advertisers use authority figures like actors dressed in white lab coats to convince consumers that a product is healthful. They often use anecdotal evidence (stories) like before and after pictures or warped statistics or single research studies that may contain bias to exaggerate the benefits of a weight loss plan or “health” food. But this type of advertising and these sorts of headlines seem to work. Consumers spend billions of dollars each year on special health foods and beverages or dietary supplements even though the scientific evidence that these substances live up to their hype is sorely lacking.

So what should we as consumers believe?  When reading nutrition-related claims, articles, websites, or advertisements always remember that one study does not substantiate a fact. One study neither proves or disproves anything. Readers who may be looking for complex answers to nutritional dilemmas can quickly misconstrue such statements and be led down a path of misinformation. Listed below are ways that you can develop discerning eyes when reading nutritional news.

1. The scientific study under discussion should be published in a peer-reviewed journal, such as the Journal of the Academy of Nutrition and Dietetics. Question studies that come from less trustworthy sources (such as non peer-reviewed journals, popular magazines, or websites) or that are not published.
2. The report should disclose the methods used by the researcher(s). Did the study last for 3 or 30 weeks? What was the “n” (number of subjects)? The longer the study and the higher the number of subjects, the more robust and credible are the results. What did the participants actually do? Did the researcher(s) observe the results themselves or did they rely on self reports from study participants? Was there a control group who did not receive the treatment so that scientists can compare one group to another?
3. Who were the subjects of this study? Humans or animals? If human, are any traits/characteristics noted? Were confounding variables assessed? How were subjects assigned to groups (randomness)? For example, the results of a study of the effects of a dietary supplement on the hearts of cardiac patients should not be used to convince an athlete to take a dietary supplement to improve their own heart’s ability to exercise. These two types of people are quite different. You may realize you have more in common with certain program participants and can use that as a basis to gauge if the study applies to you (age, biological sex, fitness level, underlying medical conditions, geographical location, etc.)
4. Credible reports often disseminate new findings in the context of previous research. A single study on its own gives you very limited information, but if a body of literature supports a finding, it gives you more confidence in it.
5. Peer-reviewed articles published in well-respected scientific journals deliver a broad perspective and are inclusive of findings of many studies on the exact same subject. By providing a list of previously published articles related to the topic, one can see how a particular study fits into the totality of the research.
6. When reading news, ask yourself, “Is this making sense?” Even if coffee does adversely affect the nervous system, do you drink enough of it to see any negative effects? Remember, if a headline professes a new remedy for a nutrition related topic, it may well be a research supported piece of news, but more often than not it is a sensational story designed to catch the attention of an unsuspecting consumer. Track down the original journal article to see if it really supports the conclusions being drawn in the news report.

There are thousands of websites that contain nutrition information. When reading information on websites, Johns Hopkins University recommends that you remember the following criteria for discerning if a site is valid and the information credible^8:

Accuracy. Does the website use reliable research? Check many sources for the same information—are the results the same?

Authority. Websites that end in .gov or .edu (and sometimes .org), are usually the most reliable websites for health facts. Make sure the website is written by doctors, dietitians, or other experts in the health field.

Bias. Who pays for the website? If a company supports a website (usually through advertising) they may have control over the website and encourage inaccurate or misleading information that promotes a need for their product or service.

Currency. When were the facts last updated? Medical research never stops. Make sure the information is no older than 3 years.

Some non-profit, non-governmental organizations like Health on the Net (HON), affiliated with the WHO, promote transparency and reliable health information on the internet. For a fee, health-related websites can have their content checked by medical experts from these organizations for accuracy and reliability. If a website becomes certified, it will be allowed to post the organization’s logo on their site for a specified time period (usually 5 years).⁹ Other organizations like the Utilization Review Accreditation Commission (URAC) have a Health Website accreditation program that looks at both content and security settings for these sites. While these certifications do not guarantee that everything on the website is accurate or reliable, it does provide some level of assurance that the information has some validity.¹⁰

Trustworthy Sources

For a list of reliable sources that advocate good nutrition to promote health and prevent disease using evidence-based science see Table 1.5.1. In Chapter 2, we will further discuss nutrition recommendations for Americans.

Table 1.5.1 Web Resources for Nutrition and Health

Portions of this chapter were taken from OER Sources listed below:

Tharalson, J. (2019). Nutri300:Nutrition. https://med.libretexts.org/Courses/Sacremento_City_College/SSC%3A_Nutri_300_(Tharalson) 

Titchenal, A., Calabrese, A., Gibby, C., Revilla, M.K.F., 7 Meinke, W. (2018). Human Nutrition. University of Hawai’i at Manoa Food Science and Human Nutrition Program Open Textbook. https://pressbooks.oer.hawaii.edu

Zimmerman, M., & Snow, B. (2012). An Introduction to Nutrition, v. 1.0. https://2012books.lardbucket.org/books/an-introduction-to-nutrition/

Additional References:

1. World Health Organization. (1946). Preamble to the Constitution of the World Health Organization as adopted by the International Health Conference. Official Records of the World Health Organization. https://www.who.int/about/who-we-are/constitution
2. Xu, J., Murphy, S. L., Kochanek, K. D., & Arias, E. (2020). Mortality in the United States, 2018. National Center for Health Statistics. Data brief, no 355. https://www.cdc.gov/nchs/products/databriefs/db355.htm
3. Klemm, S. (2019, July 15). Functional foods. Academy of Nutrition and Dietetics. https://www.eatright.org/food/nutrition/healthy-eating/functional-foods
4. Harvard Health Letter. (2019, February). Fill up on phytochemicals. Harvard Medical School. https://www.health.harvard.edu/staying-healthy/fill-up-on-phytochemicals
5. Zimmerman, M. B. (2008). Research on iodine deficiency and goiter in the 19th and early 20th centuries. The Journal of Nutrition, 138(11), 2060-63. doi:10.1093/jn/138.11.2060
6. Carpenter, K. J. (2005). David Marine and the problem of goiter. The Journal of Nutrition, 135(4), 675-80. https://doi:10.1093/jn/135.4.675
7. Briss, P.A., Zaza, S., Pappaioanou, M., Fielding, J., Wright-De Agüero, L., Truman, B. I., Hopkins, D, P., Mullen, P. D., Thompson, R. S., Woolf, S. H., Carande-Kulis, V. G., Anderson, L., Hinman, A. R., McQueen, D. V., Teutsch, S. M., & Harris, J. R. (2000). Developing an evidence-based guide to community preventive services-Methods. American Journal of Preventive Medicine, 18(1S), 35-43. https://doi:10.1016/s0749-3797(99)00119-1
8. Johns Hopkins University. (2018). Reliable health information on the internet.  https://www.hopkinsmedicine.org/johns_hopkins_bayview/_docs/patient_visitor_amenities/libraries/reliable_health_information_fall_2018.pdf
9. Health on the Net. (2020, March). https://www.hon.ch/en/
10. Utilization Review Accreditation Commission. (2020). Health website accreditation. https://www.urac.org/programs/health-web-site-accreditation