The typical diet consists of 12 to 18 percent of calories from protein. In a high-protein diet, 25 to 35 percent of calories come from protein. These diets have gained popularity as a method of weight loss; however, some health professionals are concerned that very high-protein diets may cause kidney damage.
Defining a High-Protein Diet
There are two common types of high-protein diets. The first is a diet in which some but not all carbohydrates are replaced with protein. These diets are usually low in fat. The other replaces almost all carbohydrates with protein and has a higher level of fat. Diets with extreme carbohydrate restriction lack important vitamins and minerals, including vitamin B, calcium and potassium. Ketosis may also occur with very low intakes of carbohydrate, such as less than 20 grams a day. Side effects of ketosis include increased blood acidity, electrolyte imbalances, nausea, vomiting and, in extreme cases, coma and death.
A study published in “The Journal of Nutrition" in 2004 compared weight loss in a high-protein versus a high-carbohydrate diet. The high-protein diet consisted of 30 percent of calories from protein, while the high-carbohydrate diet consisted of 60 percent of calories from carbohydrates. Even though both groups experienced an average 11-pound weight loss at the conclusion of the study, several volunteers in the high-carbohydrate group dropped out due to complaints of hunger. None of those in the high-protein group dropped out due to hunger. The study concluded that high-protein diets are more satiating, which means dieters are more likely to stick with the meal plan and lose weight or improve other markers of health.
Research published in the “American Journal of Kidney Diseases” in 2013 compared kidney function in two groups of otherwise healthy volunteers with prehypertension or early hypertension. Volunteers were fed either a high-protein diet, where 25 percent of calories were derived from protein, or a moderate-protein diet, where 15 percent of calories were derived from protein, for three weeks. At the end of the study, the kidneys of those eating the high-protein diet experienced a negative physiological response that may lead to kidney disease, although the short duration of the study does not provide conclusive evidence. For this reason, health professionals recommend obtaining a serum creatinine measurement and urinary dipstick test for proteinuria -- protein in the urine -- for those on a high-protein diet.
Large quantities of fat and carbohydrate can be stored in the body, available as a source of energy. On the other hand, protein stores are much smaller. It is beneficial to eat five to six small meals throughout the day, including protein with each. Sources of protein include one large egg, which contains 7 grams; a cup of milk, which provides 8 grams; 2 tablespoons of peanut butter, which also provides 8 grams, 1 cup of dried beans, which contains about 16 grams; or a 3-ounce piece of meat, which contains about 21 grams.