Proteins The Basis of Body Structure

Proteins The Basis of Body Structure

Proteins form important parts of the body’s main structural components: muscles and bones. Proteins also form important parts of blood, enzymes, cell membranes, and some hormones. As mentioned earlier, proteins also provide energy (4 calories per gram) for the body.

Amino Acids The building blocks of proteins are called amino acids. Twenty common amino acids are found in Nutrition The science of food and how the body TERMS uses it in health and disease.

Essential nutrients Substances the body must get from foods because it cannot manufacture them at all or fast enough to meet its needs. These nutrients include proteins, fats, carbohydrates, vitamins, minerals, and water.

Macronutrient An essential nutrient required by the body in relatively large amounts.

Micronutrient An essential nutrient required by the body in minute amounts.

Digestion The process of breaking down foods into compounds the gastrointestinal tract can absorb and the body can use.

Kilocalorie A measure of energy content in food; 1 kilocalorie represents the amount of heat needed to raise the temperature of 1 liter of water 1°C; commonly referred to as calorie.

Protein An essential nutrient that forms important parts of the body’s main structures (muscles and bones) as well as blood, enzymes, hormones, and cell membranes; also provides energy.

Amino acids The building blocks of proteins.

Nine of these are essential (or indispensable). The other 11 amino acids can be produced by the body as long as the necessary components are supplied by foods.

Complete and Incomplete Proteins Individual protein sources are considered “complete” if they supply all the essential amino acids in adequate amounts and “incomplete” if they do not. Meat, fish, poultry, eggs, milk, cheese, and soy provide complete proteins. Incomplete proteins, which come from plant sources such as nuts and legumes (dried beans and peas), are good sources of most essential amino acids but are usually low in one or more.

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Certain combinations of vegetable proteins, such as wheat and peanuts in a peanut butter sandwich, allow each vegetable protein to make up for the amino acids missing in the other protein. The combination yields a complete protein. It was once believed that vegetarians had to “complement” their proteins at each meal in order to receive the benefit of a complete protein. It is now known, however, that proteins consumed throughout the course of the day can complement each other to form a pool of amino acids the body can draw from to produce proteins. Vegetarians should include a variety of vegetable protein sources in their diets to make sure they get all the essential amino acids in adequate amounts. (Healthy vegetarian diets are discussed later in the chapter.)

Recommended Protein Intake Adequate daily intake of protein for adults is 0.8 gram per kilogram (0.36 gram per pound) of body weight, corresponding to 50 grams of protein per day for someone who weighs 140 pounds and 65 grams of protein for someone who weighs 180 pounds. Table

8.2 lists some popular food items and the amount of protein each provides.

Most Americans meet or exceed the protein intake needed for adequate nutrition. If you consume more protein than your body needs, the extra energy from protein is synthesized into fat for storage or burned for energy requirements. A little extra protein is not harmful, but it can contribute excess calories and fat to the diet because protein-rich foods can be high in fat, especially saturated fat. In 2002, the Food and Nutrition Board of the Institute of Medicine released recommendations, Acceptable Macronutrient Distribution Ranges (AMDRs), for the balance of energy sources in a healthful diet. The purpose of these recommendations is to ensure adequate intake of essential nutrients while reducing the risk of chronic diseases. A fairly broad range of protein intakes is associated with good health, and the Food and Nutrition Board recommends that the amount of protein adults eat should fall within the range of 10-35% of total

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