Protein Powder Side Effects: 4 Ways Your Shake Could Be Making You Sick


While we’re always in favor of complete and balanced meals, protein shakes can be a great way to make sure you meet your body’s muscle-building needs. But we’ve heard from countless guys that instead of kneeling at the cable machine, they end up kneeling over the toilet. The (literally) painful irony is clear: Sometimes, protein-fueled efforts at good health make people feel awful. Here’s what might be going wrong.

1. You just worked out

When you’re working out, your blood gets redirected to your muscles—and away from your stomach and digestive tract. This basically hits pause on the muscle contractions that move food through your digestive tract, aka peristalsis.

“As this shift in blood flow occurs, the shake will sit in the stomach rather than being digested quickly, and this delay can trigger a nausea response,” says Steve Hertzler, Ph.D., R.D., a senior nutrition research scientist at Abbott.

The fix: Wait a few minutes after you wrap up your last set before mixing that protein shake. Yes, your body needs fuel fast after a wicked workout—but that fuel does you no good if it’s just sloshing around in your stomach, undigested.

2. You drank it too fast

Remember being a kid and downing that ice cream cone at warp speed? You probably also remember feeling solidly (or maybe not-so-solidly) unwell afterwards. The same thing could be happening with your protein shake.

“If you’re feeling nauseous from a protein shake outside of a post-workout scenario, it may be caused by drinking the shake too quickly,” says Hertzler. Just as your digestion process is paused while you work out, digestion can also come to a halt when you eat too fast.

The fix: Slow up, dude. (And maybe think twice before becoming a professional speed-eater.)

3. You can’t tolerate the sweetener

Many protein powders are sweetened with sugar alternatives like sugar alcohols to keep calories low. Sure, they taste sweet without the calories—but your body can’t absorb them very well, which is also why they can make you sick when they’re packed into your powder. Ingredients to avoid: Sorbitol and maltitol (both sugar alcohols), and isolated fructose (not a sugar alcohol, but also a prime offender of upset stomachs).

If you’re not willing to spend calories on natural sweeteners like whole fruit or honey, stick to artificial sweeteners, which are different from sugar alcohols, Hertzler says. “Artificial sweeteners are typically used only in milligram quantities due to their intense sweetening power, lessening the chances that they would be causing gastrointestinal symptoms,” says Hertzler. And while it’s certainly possible that you have a sensitivity to one of these chemicals, they’re generally much easier on your system. Common versions are sucralose and aspartame.

The fix: Make sure you know what sweeteners (if any) are in your protein powder—and if you’re looking to switch, you might want to try something sweetened differently.

4. You’re sensitive to dairy

OK, if your protein powder is making you seriously sick, we’re guessing you’ve probably already tried switching out to a different brand. But there’s one kind of protein powder that could be making you feel ill—if you’re sensitive to dairy, at least.

Whey concentrate, the stuff in many popular protein powders, is a dense dairy product, packing in a lot of lactose with all that muscle-building protein.

“It takes about 6g of lactose (half a cup of milk) to result in evidence that lactose is not being fully absorbed from the small intestine, and about 12g lactose (1 cup of milk) before gastrointestinal symptoms start showing up,” says Hertzler.

Even lactose-heavy powders don’t pack that much lactose in a single serving. But it could still be a problem if you’re really trying to max out your protein by using several scoops.

The fix: If you think this might be a problem for you, try switching to whey isolate. Isolate is pure whey protein, stripped of all the lactose and fat that get packed into whey concentrate.

For access to exclusive gear videos, celebrity interviews, and more, subscribe on YouTube!