Protein is one of the basic building blocks of the human body, vital for building and repairing muscle. If you’re interested in gaining muscle and/or losing fat, you probably know how important it is to increase your daily intake of this macronutrient. But is there an upper limit to how much you should consume? How much protein is considered too much?
There are goalposts, but it’s hard to get over the line. Here’s what the experts say.
Are high protein diets safe?
First of all, it is very difficult to eat so much protein that it negatively affects your health. According to a study published in American Journal of Clinical Nutritionconsumed by the average American less than half from what is widely considered the “upper limit” of protein consumption: 35 percent of daily calories.
However, studies suggest that active people who exceed this upper limit may not experience any negative effects. In one 2016 study was published on Journal of Nutrition and Metabolism14 healthy resistance-trained men alternated between months of their normal diet and a “high-protein diet” (more than 3 grams per kilogram of body weight per day). To put that into context, a 154-pound person would need to eat more than 210 grams of protein per day on this diet, which equates to nearly two pounds of chicken.
After following the subjects for a year, the researchers found “no deleterious effect on blood lipid measurements as well as liver and kidney function,” where most adverse reactions to the protein would occur.
Moreover, there is research suggesting that existing recommendations may be too low for some populations, including adults over 65 years of age, pregnant and lactating women, and healthy children over 3 years of age. So while the scientific debate surrounding how much protein is too much continues, it’s important to recognize the emerging literature validating the safety and effectiveness of high-protein diets for those who need more of it.
3 Effects associated with high protein diets
While studies have explored potential risks of too much protein, the Institute of Medicine’s Dietary Intake Report states that there is “insufficient evidenceto provide causal relationships between protein and health complications, thus underscoring the need for controlled clinical studies.
1. Stomach upset/discomfort
Some people may experience gastrointestinal problems that result from taking protein supplements. This can be attributed to the lactose content in some protein drinks, such as those containing whey protein concentrate. In these cases, using whey protein isolate or plant-based protein is less likely to lead to these problems, as they contain less lactose than whey protein concentrate or none at all.
Potential gastrointestinal problems can also come from whole foods. “If you eat too much animal protein and not enough complex carbohydrates, which contain fiber, you may experience mild constipation,” explains Quyen Vu, MS, RDN.
2. Kidney problems
Some studies have reported an association between high-protein diets and renal function. However, it is “extremely rare” for exercisers to develop kidney problems or other metabolic disorders due to high protein consumption, he says Glenn Gaesser, PhD, FACSMprofessor of exercise physiology at Arizona State University.
3. Heart problems
Some research suggests that eating too much protein can affect the cardiovascular system.
“Many population-based cohort studies show a higher risk of premature mortality associated with high-protein diets, such as the classic low-carbohydrate diet, which has much more protein than the typical American diet,” says Gaesser.
However, he continues, “Higher protein intake, per se, may not be the problem, but rather other features of the diet, such as high amounts of animal fat and low amounts of fiber-rich foods.”
Can eating too much protein affect weight loss?
In a word, yes. Protein is a source of calories. If your goal is to lose weight, it’s important to create a calorie deficit, a state in which you burn more calories than you take in. If you eat so much protein that you limit (or delete) your calorie deficit, that can undermine weight loss.
“Protein not used for the body’s normal growth and maintenance functions can be used for energy if there is a shortage from other sources, and can be turned into fat,” he says. Mindy Haar, Ph.D., RDN, CDN, FANDregistered dietitian nutritionist and assistant dean at the New York Institute of Technology School of Health Professions. “If overconsumption of protein causes you to consume more calories than you need, you will gain weight.”
However, protein is still an integral part of most weight loss efforts. A meta-analysis of 24 studies found that calorie-restricted, high-protein diets produced more positive changes in total body composition than a standard-protein diet. This is likely because protein promotes fullness and can help preserve muscle.
How do you know if you’re eating too much protein?
Your first clue will probably be a stomach ache or some other minor gastrointestinal drama. Even if you have guts of steel, know that it’s possible to eat more protein than you can efficiently process.
“Your body can only use a certain amount of protein in one sitting—about 30 grams,” he says Lisa Moskovitz, RD, CDNCEO of New York Nutrition Group. “This is equivalent to about four ounces of cooked chicken breast or cooked fish, one cup of Greek yogurt, or two cups of black beans.”
It is also important to spread out your protein intake throughout the day because the body does not store excess protein.
“I see a lot in my practice that athletes try to cram their protein intake into one or two meals,” he says. Maddi Osburn, RDN, LDregistered dietitian nutritionist in Wichita, Kansas. “If an athlete consumes too much protein in one or two meals, they will not have the most optimal muscle growth response and will either be excreted or stored as fat. In addition, eating too much protein could replace other important nutrients – such as carbohydrates, fat and fiber – that are just as important for optimal recovery and performance.”
