Can Too Much Protein Cause Constipation?

Many people up their protein intake as a part of a weight-loss diet or to build muscle. And if you notice your protein supplement causes trouble in the bathroom, you're not alone. Indeed, too much protein can cause constipation — but not necessarily for the reason you think.

Eating too much animal-based protein does cause constipation or diarrhea sometimes, but the more significant factor is inadequate fiber, says gastroenterologist John Dumot, DO, director of University Hospitals Digestive Health Institute in Cleveland, Ohio. Meat contains no fiber.

So while it may feel like protein does cause constipation, in reality, it has a "weak association," he says. Really, "it's the lack of fiber."

Fiber absorbs water and adds bulk, helping to prevent both diarrhea and constipation. Adults should eat at least 28 grams a day of fiber, according to the U.S. Food and Drug Administration (FDA).

Fiber can help you have bowel movements more often, reduce overeating and decrease both blood sugar and cholesterol levels.

Meat isn't the only source of protein. So how about supplements — for instance, do protein drinks cause constipation?

If protein shakes replace a meal here and there or are used occasionally as a snack, they shouldn't cause you any digestive issues. Having protein shakes in excess, though, could bind you up, per the Cleveland Clinic.

So if you notice protein shakes constipate you, here are several reasons why the protein powder they contain can cause constipation:

Similarly to eating too much animal protein, protein shakes can cause constipation if they're not supplemented with fiber, according to the Mayo Clinic.

Remember, when you don't have much fiber in your diet, your stools can become dry, hard and difficult to pass. So if protein shakes make up a big part of your diet, consider blending in high-fiber foods like fruit or vegetables.

Protein shakes can cause constipation if you're lactose intolerant, too. That's because most protein supplements are made of whey, which contains the milk sugar lactose, according to the Cleveland Clinic.

And if your body lacks the enzymes required to digest lactose, you might feel it in your gut. The result? Protein shakes can cause constipation, diarrhea, nausea, stomach cramps or bloating.

Another potential reason why protein shakes make you constipated is that they may contain artificial sweeteners or added sugar, per the Cleveland Clinic.

These ingredients can cause constipation for some, especially if eaten as a part of a low-fiber diet, according to the National Institute on Aging.

Eating too much animal protein can make you constipated, especially if you're not getting enough fiber elsewhere in your diet. But constipation isn't the only side effect you can experience while on a high-protein diet.

"The animal-based proteins can be very hard to absorb," Dr. Dumot says, "especially in large portions usually served at restaurants and home cookouts."

The body can only process so much protein, and the excess is passed from the small intestine, where nutrients are absorbed, to the colon, where it is held until excreted in stool, he says. Excess protein in the colon can feed bacteria there associated with cardiovascular disease and colorectal cancer, Dr. Dumot says.

"They thrive on high animal protein, causing an inflammatory state," he says.

Unabsorbed protein in the gut is fermented by these bacteria, which creates a host of chemicals that boost inflammation and exacerbate colitis and other disease markers, according to a January 2019 review in ‌Microorganisms‌. These same metabolites have been associated with developing obesity, diabetes and fatty liver disease.

Getting too much protein has been linked to impaired kidney and liver function, poor bone health and disruption of the body's calcium balance, according to a July 2013 analysis of 32 studies in ‌ISRN Nutrition‌. The study authors recommended against eating more than the recommended dietary allowance (RDA) of 0.8 grams of protein per kilogram of body weight, and concluded that more research in large trials need to be done.

For an adult weighing 160 pounds, that would be 58 grams of protein a day. The FDA sets the daily value (DV) for protein at 50 grams per day for a 2,000-calorie diet.

Another concern with getting protein from animal products is saturated fat, which can raise your cholesterol level and chances of heart disease, according to the American Heart Association (AHA).

While protein doesn't typically constipate you by itself, you can become constipated from a high-protein diet that's lacking fiber or if you eat protein powder that contains ingredients that upset your stomach.

To avoid these issues, aim for no more than 5.5 ounces per day of cooked, lean red meat or fish, shellfish or skinless chicken that has not been fried, and eat protein-rich legumes and tofu in place of meat, per the AHA. That way you can avoid a diet that contains too much protein and causes constipation.

Eating a variety of fruits, vegetables and legumes is the best way to ensure you get both the fiber and all the essential amino acids — the building blocks of protein — that your body needs, he says.

"Some of the best sources of protein are plant-based," Dr. Dumot says, citing lentils and chickpeas as examples.