Protein sources and alternatives

Proteins are abundant in most plants and animals but some sources are healthier choices. For example, a high intake of red meat is linked to colon cancer in some population studies. Furthermore, red meat is high in fat and cholesterol and circulating levels of these compounds may increase the risk of heart disease. On the other hand, plant proteins contain relatively little fat and no cholesterol. If vegetable servings can be eaten with their complementary counterparts so that all the essential amino acids are regularly consumed, they may be a healthier alternative to red meats. However, vegetarians must be aware that they may not be consuming enough iron in their diet, since red meat supplies plenty of iron. Vegetarians can find iron in vegetable sources including peas, legumes and spinach.

Proteins and diets

Many weight loss strategies place emphasis on increasing the amount of protein in the diet relative to carbohydrates in order to lose weight quickly. Although it is true that amino acids cannot be directly converted to fatty acids and that some amino acids can only form ketone bodies, excess amounts can still be converted to fat when the energy level of the body is high. But high protein diets may create more serious problems. As the body begins to deplete its supply of glucose, it begins to look elsewhere for energy sources. Levels of glucagon and epinephrine increase, stimulating the release of fatty acids into the bloodstream. The breakdown of glucogenicamino acids begin to supplement the supply of glucose in the bloodstream to keep the brain and skeletal muscle functioning properly. Dietary proteins can contribute to gluconeogenesis under these conditions. Amino acids that are normally used in the building and maintenance of body tissues under conditions of adequate carbohydrate intake must now be used to meet the energy requirements of the body. This causes further protein breakdown in tissues such as the heart, skeletal muscle, and other vital organs. Meanwhile, the decrease in blood glucose creates a condition known as ketosis, or the incomplete breakdown of fats. Without sufficient oxaloacetate being produced from glucose, the Krebs Cycle cannot continue, and further metabolism at this point is thwarted. Acetyl CoA units thatare the breakdown products of fatty acids and proteins can only be converted into ketone bodies, which at high concentrations create acidic, toxic conditions for the body. Further glucogenic protein must be broken down from body tissue to produce increasingly scarce supplies of oxaloacetate. Ironically, the dieter thinks the diet is working because he or she is losing weight. Although some of the weight loss may come from adipose tissue, the majority of weight loss comes from skeletal muscle and vital organs.

Despite creating a dangerous physiological state for the dieter, he or she may have a difficult time keeping the weight off once the diet comes to an end. Decreased lean tissue mass causes a decrease in the body's resting metabolic rate. Furthermore, the absence of glucose causes the enzymes governing the breakdown of glucose to slow down in order to conserve energy. In other words, the dieter's cells have adapted to a lower energy environment. As the dieter begins to return to a normal carbohydrate diet, he or she can no longer metabolize the same amounts of glucose. Therefore, large amounts of glucose and protein are converted to fat. In conclusion, the best way for a person to lose weight is through a regular exercise routine and well-balanced meals.

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