The answer to the first part (no longer a benefit) is to stay within the range of protein intake we recommend, which is based around your activities and stage of training (adaptation phase or maintenance).

The following table details this information. You would receive no added benefit other than personal preference in consuming protein foods with an intake greater than the amounts listed under the specific conditions. Bear in mind that if you do consume beyond this level, you may actually slow your progress – keep reading.

*The protein recommendations for adaptation periods are for anabolic, not necessarily total-metabolic, purposes (e.g., satiety, performance). These protein recommendations may range from 10 to 25 percent of total caloric intake. This not only allows for differences in goals and activity, but also for bio-individuality in terms of satiety and performance. Some people respond better to slightly higher or lower protein intakes, which may help with adherence to the amount of calories required to reach and maintain goals. Individuals eating lower amounts of protein may need supplementation. Whatever the percentage of protein that ends up in relation to total caloric intake, the protein intake should still fall approximately within the above ranges of g/kg. In other words, a small person losing fat (hypocaloric) and exercising using strength and aerobic training may have a high percentage of protein (~25%) but still fall in the appropriate range of absolute protein (1.2-2.0).

The point at which excessive protein intake may harm you is more difficult to determine because there are two areas here: the first is where excess protein (beyond the recommendations in the tables) may compromise your ability to reach your goal but not necessarily harm your long-term health. In other words, by consuming protein above what is noted you would be replacing foods that make other valuable contributions to your goals that protein cannot provide or for which it would be a poor substitute. For example, protein is a poor source of energy compared to carbohydrates. Therefore, by replacing carbohydrates with protein you will likely feel less energetic and burn fewer calories, thus hindering any sport/fitness goals.

The last part of the answer related to health effects is two-fold: the first part of the answer is the same as the previous answer in that if you replace other foods that are essential to long-term health, with unnecessary protein foods, you would be short changing the body of many nutrients (vitamins, minerals, fibers, phytochemicals, etc.) that make essential contributions to living longer and more productive. The second issue is that if you chronically consume more than 4 times the RDA (>3.2gms/kg), you may at some point begin to damage organs, specifically the kidneys, but this condition is rare.

The basic rule for exercisers and athletes is that your body-composition goal determines your total daily calories and your activity determines the makeup of those calories. Therefore, meet the protein requirements listed in the table and the remaining calories will be made up of carbohydrates and fats.

Read on to learn more about the negative side effects associated with high-protein diets.

For our purposes, a high-protein diet is defined as one that consists of more than 30 percent of total caloric intake from protein, or three times the protein recommendations for athletes or ~3-4times the RDA. Chronic consumption of a high-protein diet is generally associated with a higher intake of saturated fat and low fiber intake, both of which are risk factors for heart disease and some types of cancer. Also, the kidneys are required to work harder to eliminate the increased urea produced.

Of genuine concern is the effect of high-protein diets on calcium status. For every gram of protein consumed above tissue maintenance, between 1 and 1.5 mg of calcium is excreted. America’s intake of calcium is notoriously poor. A high-protein diet, consumed by many sedentary Americans, certainly does not help in achieving calcium-intake goals.

In addition, the need for fluids is increased by high-protein intake. Protein requires approximately seven times the water for metabolism than carbohydrate or fat. Typically accompanying high-protein diets is low-carbohydrate consumption (especially for weight loss). This can lead to decreased glycogen stores, which inhibit performance and contribute to dehydration. Both of these situations will negatively affect athletic performance and overall functioning of the individual.