The United States Department of Agriculture recommends a daily protein intake of 0.8 g per pound of body weight but this number varies according to age, sex and activity level. Derived from meats, eggs, nuts, legumes, some dairy products and fortified grains, protein forms the building blocks needed for cell growth and repair. High-protein diets are sometimes touted as quick weight loss methods and are recommended for athletes as a way to build muscle. Despite the popularity of such diets, consuming more protein than your body needs may be harmful in the long run.
When you consume protein, it is digested just like any other food. Digestion by enzymes begins in the stomach and is continued in the small intestine, where the protein is broken down into smaller particles called amino acids. Amino acids are absorbed through the wall of the small intestine and transferred through the body via blood. The human body cannot store excess protein. Instead of your body using the amino acids gained from protein to build or rebuild tissue, the excess is sent to your liver. Once in the liver, excess amino acids gained from protein are either converted into other molecules or oxidized and eliminated as waste.
When proteins are changed into amino acids, ketones are released into your system. Ketones are processed by the kidneys. A diet high in protein increases ketone output and as output is increased, kidney activity also increases. The high demand placed on the kidneys as a result of excess protein consumption can encourage or exacerbate kidney disorders. Demand is also increased on the liver when unused amino acids are sent there for processing. Because of the increased demand, individuals taking in more protein than they burn are at an increased risk of liver problems.
The risks associated with excess protein consumption are generally associated with other dietary factors. The CDC mentions high-protein diets often increase caloric intake. An increased calorie intake that is greater than your need puts you at risk for weight gain. Protein derived from animal products, such as meat and eggs, are sources of saturated fat, which is linked to an increase in low-density lipoprotein, or LDL, the "bad" cholesterol that can put you at risk for heart disease when levels are elevated.
According to Katherine Zeratsky, a registered and licensed dietitian of MayoClinic.com, the long-term health effects of a diet high in protein haven't been thoroughly studied. She notes that a diet heavy in excess protein does not pose a significant risk to most individuals if followed for three to four months as a short-term method to help lose weight.
- United States Department of Agriculture: Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients) (PDF)
- Myplate.gov: How Much Food from the Protein Foods Group is Needed Daily?
- "Journal of Applied Physiology"; Evaluation of protein requirements for trained strength athletes; MA Tarnopolsky, et al.; Nov. 1992
- "International Journal of Sports Nutrition and Exercise Metabolism"; Absorption Kinetics of Amino Acids, Peptides, and Intact Proteins; AM Gabriella, et al.; August 2007
- American Heart Association: High Protein Diets
- CDC: Nutrition for Everyone: Basics - Protein