CONCEPTS IN BIOLOGY

PART VI. PHYSIOLOGICAL PROCESSES

25. Nutrition. Food and Diet

25.4. The Food Guide Pyramid

Using Dietary Reference Intakes and product labels or counting Calories is a complicated way to plan a diet. Planning a diet around basic food groups is generally easier. The USDA’s Food Guide Pyramid is a tool for planning a nutritious diet (figure 25.7). The basic philosophy of the Food Guide Pyramid is to provide simple, understandable recommendations that, when followed, will provide adequate amounts of the different kinds of nutrients. Furthermore, it is designed to limit the consumption of nutrients that can be harmful to health to acceptable levels. It also provides guidelines about exercise. The color and width of the bands refers to food groups and servings at one of many Calorie levels based on age, sex, and activity level. Go to www.pyramid.gov. Select MyPyramid Plan, type in your age, sex, height, weight, and typical physical activity to get a dietary plan that is designed for your specific needs.

FIGURE 25.7. The Food Guide Pyramid

The Food Guide Pyramid suggests that we eat certain amounts of five food groups while decreasing our intake of fats and sugars. This guide simplifies menu planning and helps us ensure that we get all the recommended amounts of basic nutrients. In order to be healthy, exercising on a regular basis is also essential.

Grains

Grains include vitamin-enriched or whole-grain cereals and products such as breads, bagels, buns, crackers, dry and cooked cereals, pancakes, pasta, and tortillas. Most of the items in this group are dry and seldom need refrigeration. Whole-grain foods contain many more nutrients (particularly vitamins and dietary fiber) than do products made with refined flours. Refined flours are made from grains but have had the outer hulls removed. What remains after the hull is removed is essentially starch. Half of the foods consumed from this group should be whole- grain products. National studies show that nearly 100 percent of the United States population consumes more refined grains than recommended.

The Food Guide Pyramid recommends that women consume 6 oz a day and men consume 8 oz a day of foods made from grains. One oz is equal to about one slice of bread or half a bagel. Grains should provide most of the energy (Calories) in the diet. Furthermore, they provide energy in the form of complex carbohydrates, such as starch, which is the main ingredient in most grain products. These foods help satisfy the appetite, and many are very low in fat. They also provide fiber, which assists in the proper functioning of the digestive tract. Foods high in fiber are also a source of several vitamins and minerals.

Significant nutritional components of grains are complex carbohydrate (starch), dietary fiber, several B vitamins, vitamin E, and the minerals iron and magnesium.

Fruits

The separation of plant foods into fruits and vegetables is sometimes confusing. Is a tomato a vegetable or a fruit? The confusion arises from the fact that the term vegetable is not scientifically precise but for nutritional purposes generally means a plant material that is not sweet and is eaten during the main part of a meal. Fruit, on the other hand, is a botanical term for the structure produced from the female part of the flower that contains the seeds. Although botanically green beans, peas, and corn are all fruits, nutritionally speaking they are placed in the vegetable category, because they are generally eaten during the main part of a meal. From a nutritional point of view, fruits include such sweet plant products as melons, berries, apples, oranges, and bananas. The Food Guide Pyramid recommends 1 to 2 cups of fruit per day, depending on age. Only about 25 percent of the U. S. population consumes the minimum recommended amount of fruit. However, because fruits tend to be high in natural sugars, the consumption of large amounts of fruits can add a significant number of Calories to the diet. In addition to cellulose in the cell walls, fruits contain many other kinds of indigestible complex carbohydrates that are important as dietary fiber.

Significant nutritional components of fruits are carbohydrate (sugars), dietary fiber, water, minerals such a potassium, and vitamin C.

Vegetables

Vegetables include nonsweet plant materials, such as broccoli, carrots, cabbage, corn, green beans, tomatoes, potatoes, lettuce, and spinach. The Food Guide Pyramid suggests 4 1/2 cups be eaten from this group each day for those who need 2,000 calories to maintain their weight and health. A cup is considered 1 cup of raw, leafy vegetables or 1/2 cup of other types. There is increasing evidence that cabbage, broccoli, and cauliflower can provide some protection from certain types of cancers. This is a good reason to include these foods in your diet. National studies indicate that most Americans do not consume at least the minimum recommended quantities of vegetables for their age and sex.

Vegetables are the primary source of many vitamins. Because different vegetables contain different kinds and amounts of vitamins, you should include many different kinds in your diet. In particular you should include some from each of the following kinds: leafy, dark green vegetables (lettuce, kale, “greens,” spinach, chard, etc.); orange vegetables (carrots, squash, sweet potatoes, pumpkin, yams, etc.); dry beans or peas; starchy vegetables (potatoes, green peas, lima beans, corn, etc.); other kinds of vegetables (cucumbers, celery, tomatoes, green beans, turnips, cabbage, egg plant, etc.). Vegetables—particularly those that are eaten raw—provide dietary fiber, which assists in the proper functioning of the digestive tract.

Significant nutritional components of vegetables are carbohydrate; fiber; several B vitamins; vitamins A, C, E, and K; and the minerals potassium, iron, and magnesium.

Milk

All of the cheeses, ice cream, yogurt, and milk are in this group. Two to 3 cups, depending on age, are recommended each day. One and one-half ounces of hard cheese is equivalent to a cup. Product labels state the appropriate serving size of individual items. Vitamin D- fortified dairy products are the primary dietary source of vitamin D. Remember that many cheeses contain large amounts of cholesterol and fat per serving. Low-fat dairy products are now recommended in the pyramid and are becoming increasingly common as manufacturers seek to match their products with the public’s desire for less fat in the diet.

Significant nutritional components of milk are protein, carbohydrate, fat, several B vitamins, vitamin D, and the minerals calcium and potassium. Some milk has vitamin A added.

Meat and Beans

This group contains most of the things we eat as a source of protein—for example, beef, chicken, fish, nuts, beans, peas, tofu, and eggs. Recall that daily protein intake is essential, because protein is not stored in the body, as are fats and carbohydrates, and that the body cannot manufacture the 10 essential amino acids, so they must be included in the diet. Animal proteins are complete proteins. The Food Guide Pyramid recommends 5.5-6.5 oz of protein per day for young adults. This means that one small hamburger meets about half of your daily needs. Most people eat many times what they need.

Because many sources of protein also contain significant amounts of fat, and health recommendations suggest reducing our fat intake, more attention is being paid to the quantity of the protein-rich foods in the diet. Beans (except for the oil-rich soybean) are excellent sources of protein without unwanted fat. Food selection and preparation are also important in reducing fat consumption. Selecting foods that have less fat, broiling rather than frying, and removing the fat before cooking all reduce fat in the diet. For example, most of the fat in chicken and turkey is attached to the skin, so removing the skin removes most of the fat.

Since the body cannot store protein, any protein consumed above what is needed to replace lost proteins is metabolized to provide energy. Eating excessive amounts of protein, however, can stress the kidneys by causing higher concentrations of calcium in the urine, can increase the demand for water to remove toxic keto acids produced from the breakdown of amino acids, and can lead to weight gain because of the intake of fat normally associated with many sources of protein.

Vegetarians must pay particular attention to acquiring adequate sources of protein, because they have eliminated a major source from their diet. They can get all the essential amino acids if they eat proper combinations of plant materials. Although nuts and soybeans are high in protein, they should not be consumed in large quantities because they are also high in fats.

Significant nutritional components of this food group are protein, fat, several B vitamins, vitamin E from seeds and nuts, and the minerals iron, zinc, and magnesium. Fish in the diet provides essential fatty acids.

Oils

The oils group includes canola, corn, olive, and sunflower oils, which are used in cooking. Some oils, such as olive, sesame, and walnut, are used to flavor foods. Small amounts of oils are important in the diet, because certain essential fatty acids cannot be manufactured by the body and must be obtained in the diet. However, because oils are fats, they have a high Caloric content. Most oils are high in monounsaturated or polyunsaturated fats and low in saturated fats. Plant oils do not contain cholesterol. Mayonnaise, some salad dressings, and soft margarine are almost entirely made of oils.

The Food Guide Pyramid recommends that for an adult, total fat intake should be between 20 and 35% of total Calories consumed daily. Most fats should be polyunsaturated and monounsaturated fatty acids, from fish, nuts, and vegetable oils. For most people this is equivalent to about 6 to 7 teaspoons of oil per day. Other recommendations are that saturated fats, trans fats, and cholesterol be as low as possible. Saturated fats come from animals and include butter, beef fat (suet), chicken fat, and pork fat (lard). Saturated fats and cholesterol are associated with the consumption of animal products, so choosing lean meats and cooking to remove fat are important for reducing total fat consumption. Unsaturated fats can be made into saturated fats by adding hydrogen (hydrogenated). When this occurs, an oil (unsaturated fat) is converted to a saturated fat. When oils are hydrogenated some of the fats are converted to trans fats. Margarine and shortening are examples of hydrogenated oils.

A few plant oils, such as coconut and palm oil, are high in saturated fats and have health effects similar to those of saturated fats from animal sources.

Significant nutritional components of oils are Calories, essential fatty acids, and vitamin E.

Exercise

Since over 65 percent of adult Americans are overweight and over 30 percent are obese, exercise is important to improving health. Therefore, exercise is included in the Food Guide Pyramid. Although it is not directly related to nutrition, the amount of exercise people get affects the number of Calories they can consume on a daily basis without gaining weight. Exercise has other health benefits as well. The pyramid recommends at least 30 minutes of moderate exercise per day; longer periods and more vigorous exercise have additional health benefits (Outlooks 25.1). Moderate exercise is that which elevates the heart rate significantly. Activities such as doing household chores or walking while shopping do not elevate heart rate and, therefore, do not count as moderate exercise. Moderate physical activities include walking briskly (about 3% miles per hour), hiking, doing gardening/yard work, dancing, golf (walking and carrying clubs), bicycling (less than 10 miles per hour), and weight training (general light workout).

The Food Guide Pyramid includes a discussion of discretionary Calories. A basic plan for any nutritional program should be to match the Calories consumed with the Calories expended and thus maintain a desirable weight. People with very active lifestyles expend more Calories and, therefore, need to consume more Calories. These Calories can come from any of the food groups simply by eating more. Extremely active persons need to add concentrated sources of carbohydrates and fats to their diet. However, these fats should still be unsaturated fats. Table 25.5 lists the Calories required for persons involved in various activities.

TABLE 25.5. Typical Energy Requirements for Common Activities

OUTLOOKS 25.1

Exercise: More than Just Maintaining Your Weight

The Food Guide Pyramid recommends 30 minutes of moderate exercise above normal daily activities. This might be a brisk walk at 3.5 miles/ hour, golfing, bicycling (10 miles/hour), and hiking. Workouts such as weight lifting—or riding a cart while golfing—do not fall into this category.

In addition to planned exercise, there are other ways to be active—such as taking the stairs instead of the elevator or escalator, parking at the far end of the lot when shopping, walking to the corner store instead of driving, or cutting the grass with a push mower instead of a riding mower.

When most people talk about exercise, they often focus on weight control. However, research in many diverse areas has revealed benefits that influence many aspects of a person's health. In addition to helping control weight, exercise:

• Increases the strength of muscles and general muscle tone

• Reduces the likelihood of injuries because of improved strength and balance

• Strengthens bones and joints; bones respond to the stress placed on them by exercise by adding bone mass

• Improves flexibility

• Increases efficiency of the respiratory system

• Increases the efficiency of aerobic respiration in mitochondria

• Heightens the immune response to better protect against infection

• Increases endorphins in the brain to reduce pain threshold and increase pleasure sensation

• Improves self-esteem and feelings of well-being

• Reduces feelings of depression and anxiety

• Helps control diabetes

• Strengthens heart muscle

• Improves cardiovascular health

• Lowers serum cholesterol

• Lowers blood pressure Improves sex life

25.4. CONCEPT REVIEW

7. Name the six basic food groups and give two examples of each.

8. Why has exercise been included in the Food Guide Pyramid?