Picture this: You just finished a KILLER workout.
You’re headed off the gym floor/track/road/bike, and ready to refuel with a satisfying whey protein shake. You need something to replenish your protein stores, give your muscles plenty of nutrients to build from, and calories to fill the empty gnawing in your stomach.
You make your shake and chug it down. Minutes later your stomach protests. Maybe you feel backed-up, maybe you’re sprinting to the bathroom.
Either way, you’re wondering: can protein shakes cause constipation or diarrhea? For some, the answer is yes.
If your whey protein is giving you an upset stomach, or you’re experiencing gastrointestinal effects like diarrhea or constipation, this article can help. Let’s walk through why it happens, how much protein your body can really handle, and the simple fixes that keep you on track for muscle recovery, without the gut side effects.
Why Your Protein Shake May Be Giving You An Upset Stomach
First, let’s talk about a few reasons your post-workout protein shake may be causing an upset stomach. Even if you’re using a high-quality, digestible protein, the way you drink it may be causing trouble inside your digestive system.
1. You drink it too soon
While it’s a good idea to refuel after a workout, drinking your protein shake too soon can lead to digestive upset, which may include diarrhea, constipation, or other gastrointestinal side effects.
When you work out, most of your body’s energy goes to supporting your muscles, limbs, and brain as they take you through your exercise routine. Your digestive system slows down to the bare minimum during challenging exercise. After you finish a workout, it takes some time for the digestive system to start up again. This means if you start eating or drinking right away, your stomach may not be ready.
Waiting 30 minutes to take your post-workout protein is a good rule of thumb to ensure adequate time for your body to “settle down” and get back into rest-and-digest mode.
2. You use too much protein powder
In the case of post-workout protein, more is not always better. If you had a particularly difficult workout, you may be tempted to add another scoop of powder to your post-workout shake. Protein is a difficult macronutrient for the body to digest, and if you take too much at once, it is almost guaranteed to cause digestive distress, especially after heavy exercise.
Keep in mind that your body is only capable of digesting a certain amount of protein at a time (generally between 25-35 grams per meal). It’s important to be aware of your body’s protein absorption rate or you’ll just be wasting your money on a supplement you drink but don’t absorb properly.
3. You drink it too quickly
It’s no surprise that after you finish a challenging workout, you’re hungry!
A liquid protein shake is easy to chug down rapidly. Doing this, however, can overwhelm your digestive system and cause your whey protein to give you an upset stomach. Not only that but when you drink something super quickly, you are likely also swallowing air. This can cause bloating and abdominal pain.
To avoid feeling completely ravenous after a workout, be sure to fuel up with a good pre-workout meal 1-2 hours before your exercise.
If you’re an endurance athlete, you may also consider consuming a highly-digestible electrolyte/protein supplement during your actual workout. This will keep your energy stores from being completely depleted during your workout and will likely help you reach your goals more easily.
How to Choose The Right Post-Workout Protein Supplement
If you’re following all the guidelines above and still experiencing a stomach ache after a protein shake-fueled workout, it may be time to look more closely at the type of protein supplement you are consuming.
Whey protein powder side effects
Whey protein is by far the most common type of protein athletes consume.
But is it the best option for you? Although whey protein does have benefits as a post-workout shake, it comes with a list of side effects for a large majority of users.
- Bloating
- Gas
- Stomach cramps
- Diarrhea
- Stuffy nose
If using whey protein in place of whole food, (for weight loss), it may also increase one’s risk of nutritional deficiencies. Always be sure to consume a balanced diet with plenty of fruits and vegetables (even when trying to lose weight) to avoid nutritional deficits.
Since these side effects are related to lactose intolerance or a milk allergy in some people, you may be able to avoid them by simply switching to a whey protein isolate or non-dairy protein alternative.
Digestibility of your post-workout protein
As we discussed earlier, it takes some time for your body to come back to the “rest-and-digest” mode after a heavy workout.
For this reason, you want to use a protein supplement that is highly digestible and takes minimum effort for your body to absorb. Pure protein is the most difficult to absorb, which is why most companies do one of two things to increase bioavailability:
- Use hydrolyzed protein
- Add digestive enzymes
Hydrolyzed collagen proteins might be the answer to protein stomach woes
You will most often find hydrolyzed protein in collagen supplements. When a protein molecule is hydrolyzed, it simply means it is broken down into smaller pieces so that your digestive system has less work to do before absorbing it and sending it off to be rebuilt by cells throughout your body. All proteins must be broken down by the digestive system anyway, so drinking hydrolyzed protein simply aids the digestive system in utilizing it more quickly.
Because a collagen protein is such a massive molecule to begin with (contains over 1,000 amino acids), the most effective collagen supplements always come in a hydrolyzed form.
Be sure to choose a high-quality brand that contains hydrolyzed collagen and is fortified with the 9 essential amino acids that make it a complete protein, like Frog Fuel Power.
In an independent study done at Kennesaw State University, our nano-hydrolyzed liquid protein shots were found to be 100% digestible within only 15 minutes. This is in sharp contrast to a leading whey protein brand, which took much longer to digest (less than 1% was digested in the first 15 minutes after consumption).
Digestive enzymes play a key role in digestion
Enzymes assist the body in breaking down the food it eats. They play a key role in digestion and absorption and are necessary for the body to receive all the nutrients it needs from the food you eat.
The body makes some enzymes on its own, and the rest come from eating whole foods or supplements containing digestive enzymes.
Some protein brands have realized that to increase the bioavailability of their protein, adding digestive enzymes is paramount. Always choose a protein supplement that contains digestive enzymes or is hydrolyzed.
Other common types of easy protein sources
While collagen and whey protein are the most commonly used by athletes, there are other types of protein to consider based on your lifestyle and unique needs. Vegetarians and vegans, for example, generally choose a plant-based protein powder made from soy or other plant-protein sources.
What Protein Supplement Is Right For Me?
When choosing a post-workout protein supplement, it is important to consider three things:
- Digestibility: Focus on proteins that are easy on the digestive system and highly absorbable. Consider a hydrolyzed protein supplement or one that contains high-quality digestive enzymes.
- Protein type: Protein type will depend on your diet and lifestyle. For most athletes, a hydrolyzed collagen supplement is a great choice because collagen is specifically used by the body to rebuild connective tissues like ligaments, skin, and muscles. Visit our article on collagen protein versus whey protein to see why we recommend hydrolyzed collagen over whey for athletes.
- Ingredients: As with anything you consume, consider all the ingredients in your protein supplement to better avoid sugars, fillers, and harmful additives. One of the most important considerations for protein supplements is finding those that offer complete proteins. Unlike Frog Fuel, there are many hydrolyzed collagen supplements NOT fortified to be complete proteins so check the label for all 22 amino acids.
Constipation & Diarrhea from Protein Shakes: Frequently Asked Questions
Can protein shakes cause constipation?
Yes. Large servings, low fiber diets, and poor hydration can slow bowel movements. Each Frog Fuel liquid collagen shot delivers 15 grams of nano-hydrolyzed, lactose-free protein that digests in about 15 minutes, so it’s far less likely to contribute to constipation when taken with adequate water and fiber intake.
Does protein powder cause constipation?
Traditional protein powders can if they’re high in lactose, low in fiber, or mixed in huge scoops. Frog Fuel isn’t a powder at all: it’s pre-digested collagen fortified to a complete amino acid profile. Because the peptides are already broken down, the gut does minimal work, which reduces the chance of stalled digestion.
Can protein shakes cause diarrhea?
They can when they’re heavy in lactose, artificial sweeteners, or bulky fillers. Frog Fuel’s formula is dairy-free, low-volume, and free of common GI irritants, making it a good option for people who experience post-shake diarrhea with standard whey drinks.
Final Notes
If you're dealing with constipation or diarrhea from your protein shake, don't write off protein supplements altogether. Instead, try switching to a hydrolyzed, complete protein like Frog Fuel, which was clinically shown to offer fast, complete absorption without the stomach issues.
