Protein keeps your hard-earned muscles happy, your stomach from growling an hour after you eat, and your metabolism humming at a fiery pace. But just like other really good things, getting tons and tons of extra protein isn't always better. Here, five weird ways your body can go haywire when you start eating insane amounts of protein. (Not sure if you're overdoing it? Use this tool to ballpark what a good amount of protein is for your body and lifestyle.)
1. Your breath smells funky.
When you cut your carbs to the bare minimum (which you're likely doing if you're on a super-high-protein diet), your body enters a state called ketosis, where it starts burning fat for fuel instead of the usual carbohydrates. Which might be great for weight loss, but not so much for your breath, said registered dietician Jessica Cording. That's because when your body burns fat, it also produces chemicals called ketones that can leave your mouth smelling sort of like you drank nail polish remover. The worst part? Since the stench is coming from inside you, brushing, flossing, or rinsing won't make much of a difference.
2. Your mood takes a dive
Maybe the Hulk-size bodybuilders at the gym are grunting because they're working crazy hard. Or maybe they're just in a crappy mood. Your brain needs carbs in all their sugary, starchy glory to stimulate the production of the mood-regulating hormone serotonin. Strip them from your diet, and you're more likely to feel grouchy, irritable, or just blah. And yes, science backs this up: One Australian study of overweight adults found that those who followed a strict low-carb diet for a year reported more crankiness compared to those who followed a higher-carb, low-fat diet—even though both groups lost roughly the same amount of weight.
3. You might wreck your kidneys.
This gets a little sciencey, but hear us out. When you chow down on protein, you also take in nitrogen byproducts that your kidneys then have to work to filter out of your blood. If you're eating a normal amount of protein, you pee out the nitrogen, and it's no big thing. But when you gorge on the muscle builder, you force your kidneys to work harder than usual to get rid of all the extra nitrogen. Which, over time, might have the potential to cause kidney damage, says Cording.
4. You're plagued with GI issues.
Chicken breast and cottage cheese are great for packing on muscle, but they deliver precisely none of the fiber that your digestive tract needs to stay regular. Which means that if you swap too many complex carbs—like whole grains, beans, vegetables, and fruit—for animal proteins, you'll have a hard time getting the recommended 25 to 35 daily grams of fiber. The result? You end up feeling constipated, bloated, and pretty much all around gross.
"It's probably the main complaint I get from my clients who have been on a low-carb diet," Cording said.
5. You gain weight.
A high-protein diet might help you drop pounds in the short-term. But if you're going hard on the egg whites and whey protein without cutting out other stuff, you're gonna gain weight, not lose it. In fact, one long-term study of more than 7,000 adults found that those who ate the most protein were 90 percent more likely to become overweight compared to people who ate less of the stuff. In other words, there's still no such thing as a miracle food. Sorry, folks!