The Stinky Side Effect of Your High Protein Diet

By putting on some muscle mass, you’re doing the future you a solid. You could be warding off chronic diseases, reducing your risk of injury, decreasing the likelihood of depression, improving your posture and maybe giving your confidence a boost. So whatever your motivation for getting some lean meat on your bones, good looking out.

The scientific consensus is that resistance training and the consumption of an adequate amount of protein will, over time, cause hypertrophy, or the enlargement of muscle tissue from increasing the size of the cells in muscle tissue. What people disagree on is how much resistance training and how much protein is needed to do the trick.

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A lot of people figure that more gym time and more protein mean the acquisition of more muscle mass and, for some people, this strategy actually might work. But by taking this “more is more” approach, they are also inadvertently increasing the statistical likelihood of two unwanted outcomes. The first is injury through overtraining, which primarily affects them. The second affects anyone unlucky enough to be standing within 15 feet of the leg press machine. I’m talking, of course, about protein farts.

You don’t have to be a meathead to produce gag-inducing flatulence, of course. But since getting serious about working out around a year ago, I’ve noticed that areas of rough air at the gym are especially pungent and have remarkably similar notes, namely that of rotten eggs. I’d unwittingly sniffed out a rather inconvenient truth about the only macronutrient that’s never out of fashion—protein.

“The amount of protein people ingest may be more than what their small intestine can readily absorb in a single sitting,” says David Kunkel, assistant clinical professor of medicine at University of California San Diego. While the small intestine makes easy work of carbohydrates, the breaking down of protein requires a little more effort. If the small intestine can’t process all of the protein as it passes through, he says, things can get funky in a hurry.

“Whatever portion of the protein that isn’t fully absorbed by the small intestine is going to hit the colon,” Kunkel says. Hiding in the colon are trillions of bacteria, ready to chow down on whatever comes their way. As they do, they carry out a metabolic process known as fermentation. “A result of fermentation are gases such as hydrogen sulfide,” he says. When these gases are expelled from our bodies as a fart, our noses pick up on it.

The link between protein consumption and building muscle mass has been known about and acted upon for a long time. And thanks to studies like this one which poured cold water on the idea that there’s a limit to the amount of protein that the body can use to maintain or build muscle mass, people looking to add brawn likely aren’t going to taper off any time soon. But compounding the problem of sulfurous compounds from large doses of protein is a newer trend among gym rats: intermittent fasting. Intermittent fasting refers to eating all your daily calories in a designated feeding window. The most popular variant entails 16 hours of fasting and eight hours in which you can eat. However, more extreme versions—which have been shown to have some health benefits—are also gaining ground, particularly among gym goers.

Kunkel, who is also a spokesperson for the American Gastroenterological Association, says that shoving all your protein into a shorter feeding window is the same as straight-up asking for olfactory trouble. Dividing up a day’s worth of protein over three or four meals spaced evenly throughout the day would reduce the likelihood of gym-goers stumbling through clouds that seemed to have emanated from the bottom of Satan himself. However, that strategy is entirely at odds with eating all of your food in an eight-, four-, or heaven forbid, one-hour window.

But while people looking to add muscle aren’t likely to suddenly eat less protein or spread it out throughout the day as a courtesy to the rest of us, there are a couple of things they can do to tamp down the issue.

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The first is to try to reduce the protein sources that contain high amounts of methionine and cysteine, says New York City-based registered dietitian, Jonathan Valdez. “These are common sulfur-containing proteins found in protein that causes the stinky smells in farts,” he says. Valdez name checks beef, turkey, fish, eggs, soy, dairy, beans, nuts, cheese, shellfish, and lamb as being high in methionine while eggs, dairy, pork, and poultry, red peppers, broccoli, onions, garlic, sprouted lentils, wheat germ, Brussel sprouts, oats, and wheat germ are high in cysteine.

Okay, so urging muscleheads to cut all of that protein-packed and/or paleo-approved stuff out probably isn’t going to work. But there is another option isn’t quite so drastic: “Probably more important than the type of protein is what you’re eating in combination with the protein, in particular, non-absorbable substances such as FODMAPs,” Kunkel says.

FODMAPs stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols. Examples of FODMAPs are certain fruits, vegetables, legumes, dairy products, and artificial sweeteners, but honey is the first thing out of Kunkel’s mouth when I ask him to call out a FODMAP that’s likely to cause offense when eaten with protein.

Given that we haven’t managed to coerce gym rats to comply with the most basic elements of gym etiquette like wiping down equipment or stifling the need to aggressively grunt, it’s unlikely that we’ll persuade them to eat less protein, spread out their protein consumption, or change their protein sources. And since most kettlebell-swinging crop-dusters aren’t smothering their steaks with honey in the first place, It seems like the best solution would be harm reduction.

Fart filtering underwear and disposable stink capture pads are already on the market but in the case of the latter, marketed as a gag gift. If Lululemon and Under Armor simply integrated this technology into their attire, it would be a gift that would prevent the rest of us from gagging.

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