Maybe you’ve noticed it after a big run: Your sweat has a strong, cloying odor, sort of like a public restroom, perhaps. You may disregard it as an inevitable byproduct of a strenuous workout, but that ammonia smell may be a red flag your diet isn’t keeping up with your energy needs.
“Your body normally metabolizes carbohydrates to create the fuel it requires for exercise,” says Dr. William Roberts, a professor of sports and family medicine at the University of Minnesota. “But if you’re exercising hard and don’t have enough carbs to meet your body’s needs, your system will switch over to protein metabolism.”
When your body breaks down protein, ammonia is one of the byproducts, Roberts explains. Normally your liver would convert that ammonia into urea, a benign organic compound that your kidneys would dispel of in the form of urine. But if you’re starved of carbs and turning to protein for most of your energy, your liver may not be able to handle all the ammonia your body produces. In those instances, your sweat becomes the vehicle through which your body jettisons all of the extra ammonia in your system.
“You see this more in people who eat low-carb and high-protein diets, or people who are over-exercisers, like ultra marathoners,” says Dr. Lewis Maharam, a New York-based physician and author of the Running Doc’s Guide to Healthy Running.
Maharam says dehydration can also contribute to the smell because it makes your sweat more concentrated. “If your urine is very dark yellow or brown, you’re not drinking enough water, and that could be part of the reason you’re smelling that ammonia.” (He’s quick to add that over-hydration is a more common issue among endurance athletes. If your pee is clear, drink less.)
The big takeaway here is that ammonia-scented sweat is not normal or healthy. “If you’re smelling ammonia in sweat, something’s wrong,” Maharam says.
Both he and Roberts agree you need to add more carbohydrates to your diet. “Whole fruits, potatoes, rice, pasta and breads are all traditional carb sources that should help correct the problem,” Roberts says. If you’re engaging in super-long workouts, sport drinks and bars tend to be carb heavy, so they can help your body avoid a switch to protein breakdown, Maharam adds.
If adding carbs to your diet doesn’t help, see a doctor. “People with liver or kidney disease also have trouble disposing of ammonia,” Roberts says. It’s also possible people on protein-heavy diets—such as Paleo—may be overburdening their systems to the point that their sweat smells like ammonia, Maharam says.
“Balance is the key to health, especially when it comes to what you’re eating,” he adds. “Going to the extreme of all protein or all fat or all carbs…none of those is good for you.”
Correction: July 9, 2019
The original version of this story mischaracterized the way that carbohydrates affect protein in the body. They help the body to avoid breaking down protein, not synthesizing it.