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Medicine LibreTexts

9.1: Nutrition and Health

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  • The foods we eat affect all dimensions of health and wellness. For example, a teen with Type 2 diabetes (a disease brought on by poor diet) is first diagnosed by physical signs and symptoms such as increased urination, thirstiness, and unexplained weight loss. But research has also found that teens with Type 2 diabetes have impaired thinking and do not interact well with others in school, thereby affecting psychological and social wellbeing. Type 2 diabetes is just one example of a physiological disease that affects multiple dimensions of health—physical, psychological, and social.

    Public Health and Disease Prevention

    In 1894, the first congressional funds were appropriated to the US Department of Agriculture (USDA) for the study of the relationship between nutrition and human health. Dr. Wilbur Olin Atwater was appointed as the Chief of Nutrition Investigations and is accoladed as the “Father of Nutrition Science” in America.Combs, G.F. “Celebration of the Past: Nutrition at USDA.” J Nutr 124, no. 9 supplement (1994): 1728S–32S.

    Under his guidance, the USDA released the first bulletin to the American public that contained information on the amounts of fat, carbohydrates, proteins, and food energy (calories) in various foods. Nutritional science advanced considerably in these early years, but it took until 1980 for the USDA and the US Department of Health and Human Services (HHS) to jointly release the first edition of Nutrition and Your Health: Dietary Guidelines for Americans. Although wide distribution of dietary guidelines did not come about until the 1980s, many historical events that demonstrated the importance of diet to health preceded their release. Assessments of the American diet in the 1930s led President Franklin D. Roosevelt to declare in his inaugural address on January 20, 1937, “I see one-third of our nation is ill-housed, ill-clad, and ill-nourished.” From the time of Atwater until the onset of the Great Depression nutritional scientists had discovered many of the vitamins and minerals essential for the functioning of the human body. Their work and the acknowledgement by President FDR of the nutritional inadequacy of the American diet evoked a united response between scientists and government leading to the enrichment of flour, the development of school lunch programs, and advancements of nutritional education in this country.

    In the latter part of the twentieth century nutritional scientists, public health organizations, and the American public increasingly recognized that eating too much of certain foods is linked to chronic diseases. We now know that diet-related conditions and diseases include hypertension (high blood pressure), obesity, Type 2 diabetes, cardiovascular disease, some cancers, and osteoporosis. These diet-related conditions and diseases are some of the biggest killers of Americans. The HHS reports that unhealthy diets and inactivity cause between 310,000 and 580,000 deaths every single year.


    As previously stated, many of the health issues associated with poor eating habits are a result of an energy imbalance. Most Americans are obtaining more energy from food than they actually need to function in their daily lives. With a large percentage of Americans engaging in no physical activity, this excess of energy is stored as fat in the body. This food energy is measured in calories, also known as kilocalories (kcals). A kilocalorie is the amount of energy needed to raise 1 kilogram of water 1 degree Celsius, but food labels use the term calorie to describe the amount of energy in the individual foods described. The term calorie is used in this textbook to describe food energy.


    Ideally, when we consume and obtain energy from our food, we will primarily eat nutrient dense foods.  A nutrient is a compound that provides a needed function in the body. Nutrients can be further classified based on the amount needed in the body. The six Essential Nutrients are the nutrients that our bodies need in order to survive. They can be broken into two categories: macronutrients and micronutrients. 

    Macronutrients are nutrients needed in larger amounts.  There are four macronutrients which include:

    • Carbohydrates: 4 calories per gram
    • Fats (lipids): 9 calories per gram
    • Protein: 4 calories per gram
    • Water: contains 0 calories 

    Note: As can be seen, carbohydrates, protein, and fats provide energy. However, there is another energy source in the diet that is not a nutrient- alcohol.

    Alcohol is NOT a nutrient! But it does provide energy. Alcohol has 7 calories per gram.

    Micronutrients are nutrients needed in smaller amounts, but they are still considered essential. There are two groups of micronutrients which are:

    • Vitamins
    • Minerals


    Carbohydrates are a diverse group of compounds that have a multitude of effects in the body and are the primary form of energy for activities of daily living. The name carbohydrate means “hydrated carbon” or carbon with water. Thus, it isn’t a surprise that carbohydrates are made up of carbon, hydrogen, and oxygen. Sucrose (table sugar) is an example of a commonly consumed carbohydrate. Although grains and starchy foods are most often associated with carbohydrates, almost all foods do contain some carbohydrates. Some dietary examples of carbohydrate rich foods are whole-wheat bread, oatmeal, rice, sugary snacks/drinks, and pasta. There are many different types of carbohydrates, but the three main types are: simple, complex, and alternative sugar sweeteners.

    Simple Carbohydrates

    Simple carbohydrates contain one molecule called monosaccharides, and double molecules are called disaccharides.


    Monosaccharides are: glucose (a major source of energy in our bodies), fructose (commonly found in fruits and used commercially in many beverages), and galactose (not normally found in nature alone but found in the disaccharide called lactose).

    Monosaccharides are sweet foods such as honey and cane sugar. Other foods that contain simple sugars are dairy products, beans, and fruit. 


    Disaccharides are: sucrose (table sugar), lactose (milk sugar), maltose (malt sugar). Disaccharides are in beverages and baked goods. They are refined for making brown sugar, powdered sugar, and molasses. Lactose is in dairy products such as cheese, yogurt, and ice cream. Maltose is found in beer and some breads and grains.

    Food manufacturers are always searching for cheaper ways to produce their food. One method that has been popular is the use of high-fructose corn syrup as an alternative to sucrose (table sugar). High-fructose corn syrup contains 55% fructose which is similar to sucrose. Nevertheless, because an increase in high-fructose corn syrup consumption has coincided with the increase of obesity in the US, there is a lot of controversy surrounding its use. In reading labels, one will usually see high-fructose corn syrup plus other sugars listed which could be adding to the obesity epidemic.

    Complex Carbohydrates

    Complex Carbohydrates contain many sugar molecules while simple carbohydrates contain only one or two sugars.  Complex Carbohydrates are called polysaccharides. Poly means “many,” and thus polysaccharides are made of more than 10 sugar molecules. (Monosaccharides are the simplest forms of sugar meaning one molecule.) There are three classes of polysaccharides: starch, glycogen, and most fibers.


    Starch is the storage form of glucose in plants. Glucose is a single sugar used in both plant and animal tissues for energy. It is the main source of fuel for the cells. After cooking, starch becomes digestible for humans. Raw starch may resist digestion. Examples of starch foods are corn, potatoes, rice, beans, pasta, and grains.


    Glycogen is made up of many glucose units (single sugar). It is made and stored by the liver and muscle tissues of humans. It is not considered a complex carbohydrate in foods.


    Fiber is indigestible matter that survives digestion in the small intestine and then reaches the large intestine. It is divided into two categories: soluble and insoluble. Soluble means it can be dissolved in water, and insoluble means it does not dissolve in water.

    • Soluble fibers are fermentable fibers. It is believed that these fibers decrease blood cholesterol and sugar levels thus lowering the risk of heart disease and diabetes II.
    • Insoluble fibers are non-fermentable, and it is believed that this type of fiber decreases the risk of constipation and colon cancer because it increases stool bulk and reduces transit time. This reduced transit time means shorter exposure to consumed carcinogens in the intestine which may lower cancer risk.

    The goal for a day’s fiber intake is 25-40 grams depending on one’s caloric intake. Suggestions would be to buy high fiber foods. Read the Nutrition Facts’ label for how much fiber is in the product for one serving. Drink lots of fluids when eating fiber. Try to eat a minimum of five plant foods for fiber each day.

    Alternative Sweeteners

    Alternative sweeteners are simply alternatives to sucrose (table sugar) and other monosaccharides and disaccharides that provide sweetness. There are basically two categories: sugar alcohol and commonly used alternative sweeteners.

    Sugar alcohol

    Sugar alcohol can provide some calories but do not contribute to tooth decay. Sugar alcohols are also known as “sugar replacers.” Some people get confused by the name sugar alcohol thinking it is a sweet alcoholic beverage.  It is not alcohol. Another name for sugar alcohols is a nutritive sweetener.  Sugar alcohols are almost as sweet as sucrose (table sugar) but only provide approximately half the calories.

    The major advantage of sugar alcohols over sucrose is that sugar alcohols are not fermented by bacteria on the tooth surface which causes less tooth decay. Sugar alcohols are listed on the Nutrition Facts’ label.

    Other Alternative Sweeteners

    Other Alternative Sweeteners have been developed to provide zero-calorie or low-calorie sweetening for foods and drinks. Because many of these provide little to no calories, these sweeteners are also referred to as non-nutritive sweeteners. (The FDA is using high-intensity sweeteners to describe these products.)

    Fats (Lipids)

    Lipids, commonly referred to as fats, have a poor reputation among most people. “Fat free” labeling on packaging is often perceived as healthy. We do need to consume certain fats, and we should try to incorporate these fats into our diets for their health benefits. However, consumption of certain fats is also associated with a greater risk of developing chronic disease(s). There are different categories of lipids:

    • Triglycerides
    • Oils
    • Cholesterol

    These compounds are grouped together because of their structural and physical similarities.  All lipids are insoluble in water, are oily to the touch, and together with carbohydrates and proteins constitute the principal structural material of the body.


    Triglycerides (triacylglycerols or TAG’s) are molecules made of glycerol and fatty acids. They are the major form of energy storage in animals. Saturated fatty acids have higher melting point than unsaturated fatty acids because they are more dense (they have more hydrogen and fewer double bonds). Animal fats usually contain more saturated fatty acids than do vegetable oils. Therefore the melting points of animal fats are higher than those of vegetable oils.

    Triglycerides are the most common lipid in our bodies and in the foods we consume. Fatty acids are not typically found free in nature; instead they are found in triglycerides. Breaking down the name triglyceride tells a lot about its structure. “Tri” refers the three fatty acids; “glyceride” refers to the glycerol backbone that the 3 fatty acids are bonded to.  Triglycerides perform the following functions in our bodies:

    • Provide energy
    • Primary form of energy storage in the body
    • Insulate and protect
    • Aid in the absorption and transport of fat-soluble vitamins.

    Structures of Fatty Acids

    Fatty acids are components of triglycerides. They are like the brick in a brick wall. Each individual brick is needed to make the overall wall. There are two basic types of fatty acids:

    • saturated fatty acid
    • unsaturated fatty acid

    These molecules differ in structure and food sources. Saturated fats are typically found in animal products such as poultry, meat and dairy and are solid at room temperature. Unsaturated fats are typically found in plants and vegetable oils and are liquid at room temperature. There are also monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (MUFAs), which appear to have a healthy affect on cholesterol levels. 

    There are two essential fatty acids, which are:

    • linoleic acid (omega-6)
    • alpha-linolenic (omega-3)

    These fatty acids are essential because the body cannot synthesize them.  The essential fatty acids are critical to human health as they play important roles in every system of the body.

    Good food sources of omega-6 include whole grains, fresh fruits and veggies, fish, olive oil, and garlic. Good food sources of omega-3 include flax seed, egg yolk, and chia seeds.

    Trans-fatty acids 

    Trans-fatty acids – like Crisco- are hydrogenated vegetable oils. In an artificial chemical process hydrogen is added to natural vegetable oils to make them more solid at room temperature, and more heat resistant for cooking. Hydrogenated oils are more resistant to heat degradation. The body doesn’t have an efficient process for using trans-fats, so they get stored for the long term. The U.S. Food and Drug Administration have determined that trans-fatty acids are no longer safe for human consumption and currently being removed from our food supply.

    Food Sources of Fatty Acids

    The figure below shows the fatty acid composition of certain oils and oil-based foods. As can be seen, most foods contain a mixture of fatty acids. Stick margarine is the only product in the figure that contains an appreciable amount of trans fatty acids. Corn, walnut, and soybean are rich sources of omega-6 polyunsaturated fatty acids while flax seed is fairly unique among plants in that it is a good source of omega-3 polyunsaturated fatty acids. Canola and olive oil are rich sources of monounsaturated fatty acids. Lard, palm oil, butter and coconut oil all contain a significant amount of saturated fatty acids.

    Types of Fat.PNG

    Figure \(\PageIndex{1}\). Different Types of Fat


    Cholesterol is a type of lipid found in the blood and in the diet. It has many functions and is a structural part of all body cells. It is an essential component of brain and nerve tissue. Cholesterol is needed to form hormones, bile, and vitamin D. Many foods contain cholesterol, but primarily it is found in foods of animal origin. Some meats are higher in cholesterol than others.

    The body needs cholesterol, but it produces all of the cholesterol that it needs. It is almost impossible to avoid consuming outside sources of cholesterol, but it is possible and advisable to limit cholesterol intake by avoiding foods high in cholesterol. Elevated levels of LDL in the blood can increase the risk of artery and heart disease.

    The human body produces two types of cholesterol: low-density lipoprotein (LDL) and high-density lipoprotein (HDL).

    LDL: The Bad Cholesterol

    LDL is cholesterol that usually enters the human body through consuming food that contains cholesterol. LDL is considered the “bad cholesterol” because it bonds with triglycerides, another lipid, and stores it within the tissues. This is the leading cause of plaque in the arteries and can lead to restricted blood flow and possible cardiac arrest. This process takes place over several years with continuous eating of saturated fats, smoking, diabetes, and high blood pressure.

    Cholesterol buildup.PNG

    Figure \(\PageIndex{2}\). Blood flow restricted by the buildup of LDL cholesterol

    Cholesterol plaque in the artery

    HDL: The Good Cholesterol

    HDL is produced when a person exercises, and it is considered the “good cholesterol.” HDL also bonds with triglycerides, but it is then processed by the body, added to feces, and expelled through the colon. In other words, HDL helps the body to process excess triglycerides thus managing the amount of excess fat in the overall system. The best way to increase HDL in the body is to exercise regularly.

    Lipid Panel

    A Lipid Panel is series of tests that measures the amount of cholesterol in the blood. A small sample of blood is drawn from the patient for this test. One number is for “total cholesterol.” This number will show the total fats in the blood. The HDL will show the good fats; LDL will show the bad fats; Triglycerides will show good or bad fats depending on the number above or below 150.

    Adult Blood Cholesterol and Triglyceride Target Numbers:

    • Total Cholesterol < 200 mg/dl
    • Total HDL > 35
    • Total LDL < 100
    • Total Triglycerides < 150


    Proteins are another major macronutrient. They are similar to carbohydrates in that they are made up of small repeating units, but instead of sugars, proteins are made up of amino acids. Protein makes up approximately 20 percent of the human body and is present in every single cell. The word protein is a Greek word, meaning “of utmost importance.” Proteins are called the workhorses of life as they provide the body with structure and perform a vast array of functions. You can stand, walk, run, skate, swim, and more because of your protein-rich muscles. Protein is necessary for proper immune system function, digestion, and hair and nail growth, and is involved in numerous other body functions. In fact, it is estimated that more than one hundred thousand different proteins exist within the human body.

    What Is Protein?


    The functions of proteins are very diverse because there are 20 distinct amino acids that form long chains. For example, proteins can function as enzymes or hormones. Enzymes, one type of protein, are produced by living cells and are catalysts in biochemical reactions (like digestion). Enzymes can function to break molecular bonds, to rearrange bonds, or to form new bonds. An example of an enzyme is salivary amylase which breaks down amylose, a component of starch.

    Amino Acids Function

    Amino acids are combined in order to form all of the protein the human body needs. In fact, the body makes proteins itself, but it needs amino acids from food to construct proteins that the body uses. Antibodies, enzymes, muscle proteins, as well as proteins in the skin are all made up of amino acids, some that the body produces and some that must be consumed.

    Non-Essential Amino

    Acids Amino acids that the body produces are called non-essential amino acids. There are eleven non-essential amino acids: alanine, arginine, asparagine, aspartate, cysteine, glutamic acid, glutamine, glycine, proline, serine and tyrosine.

    Essential Amino Acids

    In Nutrition the term essential is used to name nutrients that the body doesn’t produce itself; essential nutrients including essential amino acids must be consumed. There are nine essential amino acids:  histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.

    Complete and Incomplete Proteins

    As a way of simplifying protein, sources are described as either complete or incomplete. Complete proteins – such as eggs, tuna fish, peanut butter, almonds – contain most if not all of the essential amino acids. Incomplete proteins – such as spinach, beans, wheat germ – contain just a few of the essential amino acids.

    Most plant-based proteins are categorized as incomplete proteins, but vegetarians should not be concerned about protein intake because a person can consume all of the essential amino acids by combining food sources. For example a person can eat beans and quinoa with a spinach salad and consume the essential amino acids.


    Water is made up of hydrogen and oxygen (H2O) and is the only macronutrient that doesn’t provide energy. Humans are 65% water! The body needs water to regulate temperature, moisten tissues in the mouth, eyes, and nose, lubricate joints, protect organs, prevent constipation, reduce the burden on kidneys and liver by helping to flush out waste, and to dissolve nutrients as part of the digestive process.

    Although a person can survive for several weeks without food, the body cannot survive longer than a few days without fluids. A loss of water equivalent to:

    • 1% of body weight is enough to cause thirst and to impact the ability to concentrate
    • 4% loss of hydration results in dizziness and reduced muscle power;
    • 6% loss of fluids causes the heart to race and sweating ceases;
    • 7% loss of hydration results in collapse and subsequent death if fluids are not replaced.

    Water Intake

    Table \(\PageIndex{1}\) 

    Food Water Content (%)
    lettuce 95
    carrots 90
    boiled potatoes 80
    grapes 80
    lentil soup 78
    grilled oily fish 65
    cooked meats 60
    potato chips 52
    white bread 37
    cheddar cheese 36
    cake 15
    semi-sweet cookies 2.5
    cornflakes 3

    In a normal diet, fluid is gained via food as well as in drinks.  Along with water, most drinks such as tea, coffee, juices, and milk hydrate the body.  However, alcoholic drinks may not contribute to body fluids as alcohol is a diuretic, a substance that increases the output of urine by the body.  Caffeine, such as found in energy drinks, coffee, tea, and sodas, is also a diuretic.  Caffeine has also been shown to have an impact on overall hydration, but significant amounts (300+ mg) are typically necessary to exhibit negative effects on the body.

    The amounts of water in different foods vary.

    • Water Content of Specific Foods  

    Water Loss

    Fluid loss occurs in various ways throughout the body with urination being the primary method. While the elimination of the urine is periodic, the formation of urine constantly occurs. Urination not only removes excess water from the body but also rids the body of nitrogen-containing compounds and other wastes.  A “typical” urine output is approximately 1.5 liters daily.

    Perspiration (sweating) also removes fluid from the body.  When body temperature rises, fluids are secreted through sweat glands to the surface of the skin.  This fluid then evaporates which has a cooling effect and reduces overall body temperature.  A typical loss of water through sweating is about 0.5 liters per day.  With hot weather, exercise, or physical activity, water loss can increase to 2 liters per hour.

    Because urine output and sweating are conscious and measurable methods of fluid loss, they are called “sensible” losses.

    The body can also exhibit fluid losses in what are termed “insensible losses.”  Insensible water loss is constantly occurring every minute of every day.  These losses are neither consciously felt nor measurable.  These include events such as breathing (our expelled breath contains moisture) and defecation (feces also contain water).

    As can be seen by the above information, water intake and water loss should be balanced in order to prevent dehydration and to maintain a healthy body. The recommended daily intake is 10-13 cups of fluid from food and drink for adult males and 7-9 cups of fluid for adult females.


    Vitamins are organic compounds that are essential for normal physiologic processes in the body. Before their detailed chemical structures were known, vitamins were named by being given a letter. They are generally still referred to by that letter as well as by their chemical name, for example, vitamin C or ascorbic acid.

    Vitamins: Water-Soluble or Fat-Soluble

    Vitamins are categorized as either water-soluble or fat-soluble based on how they are dissolved in the body. Water soluble vitamins are dissolved in water and absorbed during digestion. Excess water-soluble vitamins are excreted through urine. Fat-soluble vitamins are absorbed through the digestive process with the help of fats (lipids). Excess fat-soluble vitamins can build up in the body and become toxic. Vitamin supplements can be dangerous particularly with fat-soluble vitamins because people can overdose. A balanced diet includes all of the vitamins and minerals a person needs daily.

    Water-Soluble Vitamins

    There are nine water-soluble vitamins: Vitamin C, and eight Vitamin B’s.

    Fat-Soluble Vitamins

    There are four fat-soluble vitamins: Vitamins A, D, E, and K.


    Minerals are essential, non-caloric nutrients that are in all of our food and are essential for normal physiologic processes in the body. Minerals are micronutrients, which means humans only need to eat them in small quantities. Minerals assist body functions that range from bone strength to regulating your heartbeat.

    When plants take up the water through their roots, dissolved minerals from within the soil are absorbed by the plant.  When people eat plants, they are likely ingesting minerals found in the plant. Animals are able to concentrate minerals in their tissues, so meats and other foods derived from animals often contain a higher concentration of minerals.

    There are two categories of minerals: major minerals and trace minerals. The classification of a mineral as major or trace depends on how much of the mineral the body needs. 

    Major minerals include:

    • Calcium
    • Phosphorus
    • Sodium
    • Potassium
    • Magnesium

    Trace minerals include:

    • Iron
    • Fluoride
    • Zinc
    • Copper
    • Iodine
    • Manganese
    • Chloride
    • Selenium

    Vitamin and Mineral Supplements

    Vitamin and mineral supplements exist, but are not as effective as getting minerals from whole foods. There are two types of supplement: whole food supplements and synthetic supplements.

    Whole food supplements are produced by taking vitamins and minerals straight from natural sources: soil, rocks, or plant/food sources; whereas, synthetic minerals are made in a lab. While synthetic mineral supplements mimic the chemical structure of vitamins and minerals, they are probably not exact copies. That means the body may not recognize the synthetic mineral structure and does not absorb the mineral efficiently. No supplements, including vitamins and minerals, are approved by the FDA. Only prescription drugs are approved by the FDA. A healthy balanced diet can provide all the vitamins and minerals needed.

    Food and Metabolism

    The amount of energy that is needed or ingested per day is measured in calories. A calorie is the amount of heat it takes to raise 1 g of water by 1 °C. On average, a person needs 1500 to 2000 calories per day to sustain (or carry out) daily activities. The total number of calories needed by one person is dependent on his/her body mass, age, height, gender, activity level, and the amount of exercise per day. If exercise is a regular part of one’s day, more calories are required. As a rule, people underestimate the number of calories ingested and overestimate the amount they burn through exercise. This can lead to ingestion of too many calories per day. The accumulation of an extra 3500 calories adds one pound of weight. If an excess of 200 calories per day is ingested, one extra pound of body weight will be gained every 18 days. At that rate, an extra 20 pounds can be gained over the course of a year. Of course, this increase in calories could be offset by increased exercise. Running or jogging one mile burns almost 100 calories.

    The type of food ingested also affects the body’s metabolic rate. Processing of carbohydrates requires less energy than processing of proteins. In fact, the breakdown of carbohydrates requires the least amount of energy; whereas, the processing of proteins demands the most energy. In general, the amount of calories ingested and the amount of calories burned determines the overall weight. To lose weight, the number of calories burned per day must exceed the number ingested. Calories are in almost everything one ingests, so when considering calorie intake, beverages must also be considered. Metabolic rates and calorie requirements will be discussed in further detail in the weight management chapter.


    To help provide guidelines regarding the types and quantities of food that should be eaten every day, the U.S. Department of Agriculture (USDA) has updated its food guidelines from MyPyramid to MyPlate. It has put the recommended elements of a healthy meal into the context of a place setting of food. MyPlate categorizes food into the standard six food groups: fruits, vegetables, grains, protein foods, dairy, and oils. The accompanying website gives clear recommendations regarding quantity and type of each food that one should consume each day as well as identifying which foods belong in each category. The accompanying graphic gives a clear visual with general recommendations for a healthy and balanced meal. The guidelines recommend to “Make half your plate fruits and vegetables.” The other half is grains and protein with a slightly higher quantity of grains than protein. Dairy products are represented by a drink, but the quantity can be applied to other dairy products as well.


    Figure \(\PageIndex{3}\). MyPlate provides extensive online resources for planning a healthy diet and lifestyle including offering weight management tips and recommendations for physical activity. It also includes the SuperTracker, a web-based application to help analyze one’s diet and physical activity.

    FYI: Obesity in the United States is an epidemic. IN 2010, the U.S. Centers for Disease Control and Prevention reported that nearly 36 percent of adults over 20 years old were obese and an additional 33 percent were overweight leaving only about 30 percent of the population at a healthy weight.  Research has shown that losing weight can help reduce or reverse the complications associated with obesity. The data and health issues associated with being overweight and obese will be discussed further in the weight management chapter.