The Basics of Nutrition

18 May

The Basics of Nutrition

The foods that you eat come in a vast array of colors, textures, and sizes, but they are all made up primarily of three components: carbohydrates, protein, and fats. All three of these components contain calories, meaning that they produce energy in your body. In addition to carbohydrates, protein, and fats, your body needs other nutrients, including vitamins, minerals, and water. Together these categories of nutrients are known as the building blocks of nutrition.

Carbohydrates

Carbohydrates supply the main source of energy for your body, so many nutri- tionists recommend that they should make up the majority—50 or 60 percent— of your intake of calories. Carbohydrates consist of the starches, sugars, and fiber found in foods that come from plants. There are two types of carbohydrates: sim- ple and complex. Simple carbohydrates, also known as simple sugars, taste sweet and are quickly absorbed and digested. Examples of simple carbohydrates are table sugar, honey, corn syrup, and the type of sugar found in fruit. Complex car- bohydrates refer to the starches or fiber found in rice, pasta, bread, potatoes, beans, and some fruits (such as bananas).

Complex carbohydrates are better for you than simple carbohydrates because complex carbohydrates are absorbed by your digestive system more slowly, giv- ing your body a more sustained source of energy and preventing steep rises and falls in blood sugar levels. They also contain many nutrients, such as vitamins and minerals, while the simple carbohydrates in foods such as candy, pastries, and other sugary desserts provide only calories. By far, most of the carbohy- drates you consume should be the complex carbohydrates found in grains (preferably whole grains), vegetables, and fruits.

The problem with sugar and foods containing high amounts of sugar is that they supply “empty calories”—that is, they contain many calories but no nutri- ents. For example, one 12-ounce can of soda contains about 9 teaspoons of sugar. Sugary desserts taste good, but when you fill up on simple sugars, you leave no room for more nutrient-rich foods. Sweet desserts often also contain large amounts of fat; the high consumption of fat has been shown to have health risks. Overindulgence in these foods also leads to excess weight gain.

Fiber is a special type of carbohydrate that is found in foods such as whole bran and other grains, vegetables, and fruits. Fiber is the part of the plant that is not digestible and provides no nutrients, but it has many beneficial health func- tions. It comes in two forms: soluble and insoluble. Soluble fiber, present in oat bran and oatmeal, barley, dried beans, vegetables, and fruits, can improve your blood cholesterol levels (see page 89), especially when consumed as part of a low-fat diet. Insoluble fiber is found in whole bran cereals, whole-wheat bread, and fruit and vegetable skins. Its main function is to increase the bulk in your stools, thereby preventing constipation and protecting against certain other digestive disorders, such as colon cancer. Eating according to the Food Guide Pyramid (see page 5) will easily provide the recommended 25 grams of fiber per day.

If you want to begin increasing your intake of fiber, do it gradually, because a sudden increase can cause abdominal bloating and excess intestinal gas. Drink plenty of water to minimize these effects. Your body will eventually adapt to the higher levels of fiber. Doctors do not usually recommend fiber supplements because they lack the vital nutrients found in whole grains, vegetables, and fruits.

Protein

The primary function of protein-rich foods is to form muscle, bone, and skin and to repair body tissue. Certain proteins also carry hormones and other essential elements throughout your body by way of the bloodstream. Protein-rich foods include meat, poultry, fish, eggs, dried beans, nuts, and dairy products. Grain foods such as breads and cereals are a secondary source of protein.

Proteins are made up of combinations of 21 different chemicals called amino acids. Nine of these chemicals, called essential amino acids, cannot be manu- factured by your body and must be obtained from the food you eat. Others, known as nonessential amino acids, are made from the essential type. Proteins from animal sources are called complete proteins because they are rich in essen- tial amino acids. Because proteins in plant foods such as beans or nuts have fewer of the essential amino acids, they are referred to as incomplete proteins. In the past doctors and nutrition experts recommended combining plant proteins such as rice and beans at a given meal to ensure getting enough essential amino acids. But unless you have a protein deficiency, which is rare in the United States, or are a vegetarian, the experts now know that combining proteins is unnecessary as long as your total diet is balanced.

Many men believe that they need to consume an abundance of protein to eat healthfully, but the Recommended Dietary Allowance (RDA) for protein set by the Food and Nutrition Board of the National Research Council is actually quite low. The RDA for protein is 63 grams per day for an adult male, which is about 10 to 15 percent of your total calorie intake. Consuming this amount of protein each day is not difficult. Simply eat 6 to 8 ounces of meat, poultry, or fish and drink a couple of glasses of milk and you have met your RDA. Most Americans eat more protein than that each day—more than they need.

Fat

Fat enhances the flavor and texture of food, which helps explain why high-fat foods usually taste good. Fat has important functions in the body, including help- ing to make the male hormone testosterone. But most people in developed coun- tries consume too much fat, which leads to the development of heart disease,

some types of cancer, and other chronic diseases. This explains why the Dietary Guidelines for Americans (see page 6) advises deriving no more than 30 percent of your total calorie intake from fat, and no more than 10 percent of total calories from saturated fat (see below).

There are three main types of fat in the foods you eat: saturated, polyunsatu- rated, and monounsaturated. Cholesterol is also a type of fat found in foods of animal origin. Don’t be confused by the difference between the cholesterol found in food and the cholesterol that circulates in your blood. Your liver manu- factures most of the cholesterol in your blood from the saturated fat you con- sume; a smaller percentage comes from the cholesterol in the food you eat. Some men’s blood cholesterol levels are affected more than other men’s by the amount of cholesterol they eat. Having a high cholesterol level increases your risk of heart disease.

Another category of fat, known as trans fatty acids, also is present in certain foods. Trans fatty acids are synthetic fats made during food processing. The fol- lowing table describes the differences in the various types of fats.

Understanding Dietary Fats

Water

Water is an essential nutrient, just like the nutrients in food. Your body is made up primarily of water, which accounts for 50 to 80 percent of your body weight. Your requirement for water varies, depending on such factors as the temperature and humidity or your activity level. Water loss through perspiration during physical exertion can increase your body’s need for water dramatically. Having

diarrhea also can cause excess water loss from your intestines, so it’s important to drink plenty of fluids when you have a bout of diarrhea.

In general, thirst is the best indicator that you need water. Don’t quench your thirst with caffeinated soda or alcoholic beverages because caffeine and alcohol will only dehydrate you further. Older people may find that their thirst sensation has become dulled. If you are an older man, remember to drink at least eight glasses of water and other fluids, 8 ounces each, every day, regardless of whether you are thirsty, and especially in hot weather. It’s easy to become dangerously dehydrated without realizing it when the weather is hot and humid.

The federal government sets standards for the safety and purity of drinking water, and most municipalities meet these guidelines. Occasionally, however, contaminants enter public drinking water supplies. If you are told that your local water facility is having problems with high bacteria counts or other contamina- tion, boil your tap water before you drink it or use it for cooking. The plumbing in older homes sometimes leeches lead into tap water. If you suspect that your plumbing might have lead-containing solder, run your tap water for several min- utes every morning before drinking it. Always use cold water when cooking because hot water can cause lead to leech from pipes even faster.

Fluoride is an element that occurs naturally in the water found in some parts of the United States. In other regions, local municipalities add fluoride to public water supplies to help prevent tooth decay. Fluoridation of water is safe and is largely responsible for a substantial nationwide decrease in tooth decay.


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