Your body requires protein for a variety of purposes. It uses the amino acids from protein to make hormones, enzymes, carrier proteins, and antibodies, components of your immune system that help fight infection. Plus, your body uses the amino acids from protein for repair, including the restoration of muscle tissue. When you do a resistance workout, you damage muscle fibers and they have to be repaired and remodeled. The amino acids from protein are what goes into rebuilding those fibers. Less commonly, the amino acids from protein are used as fuel. It’s only during periods of starvation or low blood sugar that protein becomes a significant fuel source.
Ask fitness experts how much protein someone who exercises needs and you’ll get a variety of opinions. Most agree that you need more protein if you strength train or do lots of endurance exercise. The American College of Sports Medicine recommends 1.2 to 2.0 grams of protein per kilogram of body weight daily. If you train harder or more often, you would best be served toward the higher end of the range where you would need less if you train less frequently or less intensely. But, what if you were to exceed this amount of protein? Is it possible to get TOO much protein in your diet?
Are There Health Risks Associated with Too Much Protein?
At one time, there were concerns that consuming too much protein could be harmful to the kidneys. However, those concerns are unfounded in people with normal, healthy kidneys. In fact, a study published in the Internal Journal of Sports, Nutrition, Exercise, and Metabolism found that consuming up to 2.8 grams of protein per kilogram of body weight was not associated with adverse health effects, although this was a short-term study.
One word of caution though. One study found that rapidly increasing protein content (from 1.2 grams/kg. to 2.4 grams/kg.) was associated with higher levels of protein breakdown products in the blood. The researchers hypothesize that with such a rapid increase the kidneys had a hard time clearing the protein, an example of too much too quickly. This raises some concern about suddenly increasing the amount of protein you consume. Also, it’s clear that people with kidney problems should avoid taking in large quantities of protein.
For the most part, assuming the kidney function is normal, and the amount of protein consumed isn’t suddenly increased, the kidneys can handle a high-protein intake. You filter more protein through your kidneys with higher protein intake but a healthy kidney can handle this. But, there’s another organ affected by protein intake – the liver. A healthy liver seems capable of handling substantial quantities of protein, although there is some evidence in rodents that consuming lots of protein after fasting may be damaging to the liver. This hasn’t been studied in humans. People who have liver disease must reduce their protein consumption to avoid build-up of toxic levels of ammonia in the blood.
Of more recent concern is a study presented at the International Liver Congress. This study looked at food-frequency questionnaires from 3,400 people with non-alcoholic fatty liver disease. It showed that participants who consumed a higher quantity of calories from protein were 37% more likely to develop non-alcoholic fatty liver disease. Non-alcoholic fatty liver disease, or NAFLD, is at epidemic proportions in western countries and many people don’t know they have it. In fact, around 35% of the population has it. NAFLD is strongly linked to being overweight or obese. On a bright note, the link was with animal protein, not plant-based protein. Although this is a single, observational study, it does suggest that consuming a higher ratio of plant-based to animal-based protein might be safer than eating purely animal-based protein.
Do You Really Need That Much Protein?
Although there isn’t strong evidence that consuming large amounts of protein is risky, based on short-term studies, do you really need to consume a high-protein diet? Evidence suggests that you need more protein if you exercise as you’re shuttling amino acids from the protein you eat into repairing your muscles. However, beyond a certain amount, there’s no additional benefit.
Most studies looking at how the body handles protein use nitrogen balance studies but this method has shortcomings. One study used another method called Indicator Amino Acid Oxidation (IAAO) technique, a way of testing that lacks some of these shortcomings. When researchers used this technique to measure protein requirements in a group of young, healthy bodybuilders, it showed that consuming between 1.2 to 2.2 grams of protein per kilogram of body weight is sufficient, with an average of 1.7 grams sufficing for the average bodybuilder. Beyond this point, you’re unlikely to see additional gains in strength or muscle hypertrophy based on protein intake.
Keep in mind that the participants in the study were young and male. It could be that older people and females require more or less. Also, these values pertain to protein requirements on non-training days. They may be slightly higher on training days when your body is actively repairing itself.
The Bottom Line
There’s no evidence that consuming more protein is harmful to organs like the kidneys or liver in healthy adults with normal kidney and liver function. However, there is a limit to how much protein your body can use and there’s no added benefit to consuming excess. However, as the IAAO study suggests, the amount the average bodybuilder can use to maximize gains is fairly high, around 1.7 grams per kilogram of body weight daily, at least for males.
Another precaution. When you consume a diet higher in protein, you need to drink more water as metabolism and excretion of protein increases fluid requirements. It’s important to drink enough water anyway, especially if you work out.
Academy of Nutrition and Dietetics. “Protein and the Athlete — How Much Do You Need?”
Int J Sport Nutr Exerc Metab. 2000 Mar;10(1):28-38.
Am J Clin Nutr. 2009 Dec;90(6):1509-16. doi: 10.3945/ajcn.2009.27601. Epub 2009 Oct 7.
Time Magazine. “Why Eating More Protein Isn’t Always Better” April 28, 2017.
Examine.com. “Should one gram per pound be the new RDA for bodybuilders?”
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