3. Metabolism and Nutrition

Nutrition and Diet

The carbohydrates, lipids, and proteins in the foods you eat are used for energy to power molecular, cellular, and organ system activities. Importantly, the energy is stored primarily as fats. The quantity and quality of food that is ingested, digested, and absorbed affects the amount of fat that is stored as excess calories. Diet—both what you eat and how much you eat—has a dramatic impact on your health. Eating too much or too little food can lead to serious medical issues, including cardiovascular disease, cancer, anorexia, and diabetes, among others. Combine an unhealthy diet with unhealthy environmental conditions, such as smoking, and the potential medical complications increase significantly.

Food and Metabolism

The amount of energy that is needed or ingested per day is measured in calories. The nutritional Calorie (C) is the amount of heat it takes to raise 1 kg (1000 g) of water by 1 °C. This is different from the calorie (c) used in the physical sciences, which is the amount of heat it takes to raise 1 g of water by 1 °C. When we refer to “calorie,” we are referring to the nutritional Calorie.

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 their body mass, age, height, gender, activity level, and the amount of exercise per day. If exercise is 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 you ingest, so when considering calorie intake, beverages must also be considered.

To help provide guidelines regarding the types and quantities of food that should be eaten every day, the USDA has updated their food guidelines from MyPyramid to MyPlate. They have 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 you should consume each day, as well as identifying which foods belong in each category. The accompanying graphic (Figure 24.24) 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.

The figure shows a plate with different food groups assigned different portion sizes.

Figure 24.24 MyPlate The U.S. Department of Agriculture developed food guidelines called MyPlate to help demonstrate how to maintain a healthy lifestyle. 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 you analyze your own diet and physical activity.


Vitamins are organic compounds found in foods and are a necessary part of the biochemical reactions in the body. They are involved in a number of processes, including mineral and bone metabolism, and cell and tissue growth, and they act as cofactors for energy metabolism. The B vitamins play the largest role of any vitamins in metabolism (Table 24.3 and Table 24.4).

You get most of your vitamins through your diet, although some can be formed from the precursors absorbed during digestion. For example, the body synthesizes vitamin A from the β-carotene in orange vegetables like carrots and sweet potatoes. Vitamins are either fat-soluble or water-soluble. Fat-soluble vitamins A, D, E, and K, are absorbed through the intestinal tract with lipids in chylomicrons. Vitamin D is also synthesized in the skin through exposure to sunlight. Because they are carried in lipids, fat-soluble vitamins can accumulate in the lipids stored in the body. If excess vitamins are retained in the lipid stores in the body, hypervitaminosis can result.

Water-soluble vitamins, including the eight B vitamins and vitamin C, are absorbed with water in the gastrointestinal tract. These vitamins move easily through bodily fluids, which are water based, so they are not stored in the body. Excess water-soluble vitamins are excreted in the urine. Therefore, hypervitaminosis of water-soluble vitamins rarely occurs, except with an excess of vitamin supplements.Fat-soluble Vitamins

Vitamin and alternative nameSourcesRecommended daily allowanceFunctionProblems associated with deficiency
retinal or β-carotene
Yellow and orange fruits and vegetables, dark green leafy vegetables, eggs, milk, liver700–900 µgEye and bone development, immune functionNight blindness, epithelial changes, immune system deficiency
Dairy products, egg yolks; also synthesized in the skin from exposure to sunlight5–15 µgAids in calcium absorption, promoting bone growthRickets, bone pain, muscle weakness, increased risk of death from cardiovascular disease, cognitive impairment, asthma in children, cancer
Seeds, nuts, vegetable oils, avocados, wheat germ15 mgAntioxidantAnemia
Dark green leafy vegetables, broccoli, Brussels sprouts, cabbage90–120 µgBlood clotting, bone healthHemorrhagic disease of newborn in infants; uncommon in adults

Table24.3Water-soluble Vitamins

Vitamin and alternative nameSourcesRecommended daily allowanceFunctionProblems associated with deficiency
Whole grains, enriched bread and cereals, milk, meat1.1–1.2 mgCarbohydrate metabolismBeriberi, Wernicke-Korsakoff syndrome
Brewer’s yeast, almonds, milk, organ meats, legumes, enriched breads and cereals, broccoli, asparagus1.1–1.3 mgSynthesis of FAD for metabolism, production of red blood cellsFatigue, slowed growth, digestive problems, light sensitivity, epithelial problems like cracks in the corners of the mouth
Meat, fish, poultry, enriched breads and cereals, peanuts14–16 mgSynthesis of NAD, nerve function, cholesterol productionCracked, scaly skin; dementia; diarrhea; also known as pellagra
pantothenic acid
Meat, poultry, potatoes, oats, enriched breads and cereals, tomatoes5 mgSynthesis of coenzyme A in fatty acid metabolismRare: symptoms may include fatigue, insomnia, depression, irritability
Potatoes, bananas, beans, seeds, nuts, meat, poultry, fish, eggs, dark green leafy vegetables, soy, organ meats1.3–1.5 mgSodium and potassium balance, red blood cell synthesis, protein metabolismConfusion, irritability, depression, mouth and tongue sores
Liver, fruits, meats30 µgCell growth, metabolism of fatty acids, production of blood cellsRare in developed countries; symptoms include dermatitis, hair loss, loss of muscular coordination
folic acid
Liver, legumes, dark green leafy vegetables, enriched breads and cereals, citrus fruits400 µgDNA/protein synthesisPoor growth, gingivitis, appetite loss, shortness of breath, gastrointestinal problems, mental deficits
Fish, meat, poultry, dairy products, eggs2.4 µgFatty acid oxidation, nerve cell function, red blood cell productionPernicious anemia, leading to nerve cell damage
ascorbic acid
Citrus fruits, red berries, peppers, tomatoes, broccoli, dark green leafy vegetables75–90 mgNecessary to produce collagen for formation of connective tissue and teeth, and for wound healingDry hair, gingivitis, bleeding gums, dry and scaly skin, slow wound healing, easy bruising, compromised immunity; can lead to scurvy



Minerals in food are inorganic compounds that work with other nutrients to ensure the body functions properly. Minerals cannot be made in the body; they come from the diet. The amount of minerals in the body is small—only 4 percent of the total body mass—and most of that consists of the minerals that the body requires in moderate quantities: potassium, sodium, calcium, phosphorus, magnesium, and chloride.

The most common minerals in the body are calcium and phosphorous, both of which are stored in the skeleton and necessary for the hardening of bones. Most minerals are ionized, and their ionic forms are used in physiological processes throughout the body. Sodium and chloride ions are electrolytes in the blood and extracellular tissues, and iron ions are critical to the formation of hemoglobin. There are additional trace minerals that are still important to the body’s functions, but their required quantities are much lower.

Like vitamins, minerals can be consumed in toxic quantities (although it is rare). A healthy diet includes most of the minerals your body requires, so supplements and processed foods can add potentially toxic levels of minerals. Table 24.5 and Table 24.6 provide a summary of minerals and their function in the body.Major Minerals

MineralSourcesRecommended daily allowanceFunctionProblems associated with deficiency
PotassiumMeats, some fish, fruits, vegetables, legumes, dairy products4700 mgNerve and muscle function; acts as an electrolyteHypokalemia: weakness, fatigue, muscle cramping, gastrointestinal problems, cardiac problems
SodiumTable salt, milk, beets, celery, processed foods2300 mgBlood pressure, blood volume, muscle and nerve functionRare
CalciumDairy products, dark green leafy vegetables, blackstrap molasses, nuts, brewer’s yeast, some fish1000 mgBone structure and health; nerve and muscle functions, especially cardiac functionSlow growth, weak and brittle bones
PhosphorousMeat, milk700 mgBone formation, metabolism, ATP productionRare
MagnesiumWhole grains, nuts, leafy green vegetables310–420 mgEnzyme activation, production of energy, regulation of other nutrientsAgitation, anxiety, sleep problems, nausea and vomiting, abnormal heart rhythms, low blood pressure, muscular problems
ChlorideMost foods, salt, vegetables, especially seaweed, tomatoes, lettuce, celery, olives2300 mgBalance of body fluids, digestionLoss of appetite, muscle cramps

Table24.5Trace Minerals

MineralSourcesRecommended daily allowanceFunctionProblems associated with deficiency
IronMeat, poultry, fish, shellfish, legumes, nuts, seeds, whole grains, dark leafy green vegetables8–18 mgTransport of oxygen in blood, production of ATPAnemia, weakness, fatigue
ZincMeat, fish, poultry, cheese, shellfish8–11 mgImmunity, reproduction, growth, blood clotting, insulin and thyroid functionLoss of appetite, poor growth, weight loss, skin problems, hair loss, vision problems, lack of taste or smell
CopperSeafood, organ meats, nuts, legumes, chocolate, enriched breads and cereals, some fruits and vegetables900 µgRed blood cell production, nerve and immune system function, collagen formation, acts as an antioxidantAnemia, low body temperature, bone fractures, low white blood cell concentration, irregular heartbeat, thyroid problems
IodineFish, shellfish, garlic, lima beans, sesame seeds, soybeans, dark leafy green vegetables150 µgThyroid functionHypothyroidism: fatigue, weight gain, dry skin, temperature sensitivity
SulfurEggs, meat, poultry, fish, legumesNoneComponent of amino acidsProtein deficiency
FluorideFluoridated water3–4 mgMaintenance of bone and tooth structureIncreased cavities, weak bones and teeth
ManganeseNuts, seeds, whole grains, legumes1.8–2.3 mgFormation of connective tissue and bones, blood clotting, sex hormone development, metabolism, brain and nerve functionInfertility, bone malformation, weakness, seizures
CobaltFish, nuts, leafy green vegetables, whole grainsNoneComponent of B12None
SeleniumBrewer’s yeast, wheat germ, liver, butter, fish, shellfish, whole grains55 µgAntioxidant, thyroid function, immune system functionMuscle pain
ChromiumWhole grains, lean meats, cheese, black pepper, thyme, brewer’s yeast25–35 µgInsulin functionHigh blood sugar, triglyceride, and cholesterol levels
MolybdenumLegumes, whole grains, nuts45 µgCofactor for enzymesRare


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