1. NUTRITION AND NUTRIENTS

2. Nutrition is the study of nutrients and how the body utilizes them. Nutrients include carbohydrates, lipids, proteins, vitamins, minerals, and water. Macronutrients (needed in large amounts) include carbohydrates, lipids, and proteins. Macronutrients provide the body with energy. Vitamins and minerals are called micronutrients because they are required in smaller amounts. Micronutrients do not directly provide energy, but make possible the reactions that extract energy from macronutrients.

3. Calories measure the potential energy in food. One gram of protein or carbohydrate equals about 4 calories, whereas one gram of fat equals about 9. Foods provide nutrients and digestion breaks them down to sizes that can be absorbed and transported in the bloodstream. Nutrients that human cells cannot synthesize are called essential nutrients.

4. Carbohydrates are organic compounds used primarily to supply energy for cellular processes. Starch, glycogen, disaccharides, and monosaccharides are all carbohydrates. The body absorbs the monosaccharides (simple sugars) fructose, galactose, and glucose. Cellulose is a complex carbohydrate the body cannot break down. Cellulose provides bulk (fiber) which helps move food along the alimentary canal. Glucose is the body’s fuel source. Excess glucose is stored as glycogen or converted to fat.

5. To obtain energy, the body first metabolizes glucose, then glycogen, and finally fats and proteins. Carbohydrates also serve as the starting material for vital biochemicals such as ribose, deoxyribose, and lactose in breast milk. The requirement for carbohydrates varies with individual energy expenditure. In a low carbohydrate diet, calories from carbohydrates should be 20-25% of your daily intake. Excess carbohydrates may lead to weight gain.

6. Lipids are organic compounds that supply energy for cellular processes and for building structures such as cell membranes and steroid hormones. Lipids include fats, phospholipids, and cholesterol. The most common dietary lipids are the fats called triglycerides. Tryglycerides are part of both plant and animal-based foods. Saturated fats are found primarily in foods of animal origin. Unsaturated fats are found in foods of plant origin. Monounsaturated fats are the healthiest.

7. Cholesterol is found only in animal-based foods. The liver controls the amount of cholesterol in the body by synthesizing and releasing it into the blood stream, and by removing cholesterol and excreting it into bile or by making bile salts. The liver and adipose tissue control tryglyceride metabolism. The liver can convert fatty acids from one form into another, but cannot synthesize essential fatty acids such as linoleic and linolenic acid.

8. The amounts and types of fats required for health vary with an individual’s habits and goals. Fat intake must be sufficient to carry fat-soluble vitamins. The USDA and American Heart Association recommend that lipid intake not exceed 30% of calories.

9. Proteins are polymers of amino acids that serve as structural materials, function as enzymes, and provide energy. Foods rich in proteins include meats, fish, poultry, cheese, nuts, milk eggs, and cereals. Legumes (beans and peas) contain lesser amounts. Adult cells can synthesize all but eight required amino acids. Amino acids that the body can synthesize are termed nonessential; those that it cannot synthesize are essential amino acids. They include isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

10. All of the amino acids must be present in the body at the same time for growth and tissue repair to occur. In other words, if one essential amino acid is missing for the diet, normal protein synthesis cannot take place. Complete proteins contain adequate amounts of the essential amino acids. Incomplete proteins are unable by themselves to maintain human tissues or to support normal growth and development.

11. The amount of dietary protein individuals require varies according to body size, metabolic rate, and other factors, such as activity level. To estimate desirable protein intake, divide your weight in pounds by two. Most people should consume between 60 to 150 grams of protein a day.

12. Vitamins are organic compounds that are required in small amounts for normal metabolism, but that cells cannot synthesize in adequate amounts. Vitamins are classified based on solubility. Fat-soluble vitamins include vitamins A, D, E, and K. They are carried in lipids and can accumulate in various tissues, which is why excess can lead to overdose conditions. Fat-soluble vitamins resist the effects of heat; thus, cooking and food processing does not destroy them.

13. Water-soluble vitamins include the B vitamins and vitamin C. B vitamins usually occur together in foods and are called the vitamin B complex. They are essential for normal cellular metabolism. Vitamin C is found in plant foods and has a variety of functions.

14. Minerals are elements other than carbon that are essential in human metabolism. Humans obtain minerals from plant foods or from animals that have eaten plants (herbivores). Minerals are responsible for about 4% of body weight and are most concentrated in the bones and teeth. Minerals are usually incorporated into organic molecules, but some occur in inorganic compounds or as free ions. They serve as structural materials, function in enzymes, and play vital roles in metabolism.

15. Major minerals include calcium, phosphorus, potassium, sulfur, sodium, chlorine, and magnesium. By weight, major minerals make up the bulk of minerals in the body. Trace elements are essential minerals found in minute amounts. They include iron, manganese, copper, iodine, cobalt, zinc, fluorine, selenium, and chromium.

16. Adequate diets provide sufficient energy and essential nutrients to support optimal growth, maintenance, and repair of tissues. Individual requirements vary so greatly that designing a diet that is adequate for everyone is not possible. Food guide pyramids help to personalize diets. If the diet lack essential nutrients or a person fails to use available foods to their best advantage malnutrition sets in.

17. A measurement called the body mass index (BMI) is used to determine whether a person is of adequate weight, overweight, or obese. To calculate your BMI, divide your weight in kilograms (1 kg = 2.2 lbs) by your height in meters squared (1 ft = 0.3 meters). A BMI between 18.5 and 24.9 is considered normal.