Can protein make you poo?

Protein is the macronutrient that can do no wrong. Not only is it essential for muscle growth, it also helps you to maintain healthy blood-sugar levels; increase satiety so you don’t overeat and fail to hit your racing weight; help your bloodstream carry oxygen throughout your body, ensuring working muscles are swim, bike and running to their optimum; and even work with your body to create antibodies to fend off illness and infection.

So, all good…? Well, maybe not, as there’s certainly evidence that protein can both make you poo and make you not poo…

But first up, let’s work back… The recommend daily amount of protein intake is around 0.8g of protein per kilogramme bodyweight. That means a 70kg individual should aim for around 56g protein each day.

But not if they’re a triathlete or fellow committed sports(wo)man as the American College of Sports Medicine and the International Society for Sports Nutrition advise that active adults should aim for a higher daily protein intake of around 1.2 to 2g per kilogramme bodyweight. For the 70kg athlete, that means around 84 to 140g protein each day.

Just note that it’s not simply a case of the more protein the better. For an athlete, you’re looking to pack your working body with carbohydrates and good fats, too, so excessive protein can limit your intake of these two other vital macronutrients.

There’s also evidence that regularly consuming more than 2g of protein per kilogramme bodyweight is actually detrimental to your health with a 2022 study in the Journal of the American Society of Nephrology revealing that too much protein can be problematic with individuals who have pre-existing kidney disease (of which they might be unaware).

What’s the best source of protein?

That’s the amount of protein taken care of. But where do you source that protein from? With a well-rounded diet, that’s where, which should include many of the following foods…

• Lean or low-fat meat and poultry, such as chicken, turkey, beef, pork, lamb and bison
• Fish. Cod, trout, salmon and tuna are good choices
• Shellfish, including shrimp, oysters, clams, mussels and scallops
• Eggs
• Unsalted nuts, such as walnuts, pistachios, almonds and cashews
• Seeds, like sunflower seeds, pumpkin seeds, flax seeds and chia seeds
• Beans, peas and lentils, like edamame, black beans, pinto beans, chickpeas and lima beans
• Soy products, such as tofu and tempeh
• Low-fat milk, including dairy and plant-based milk. Avoid milk with added sugar
• Low-fat cottage cheese
• Yoghurt. Go for low- or no-sugar varieties
• Cheese
• Whole grains, like oats, quinoa, brown rice and wild rice.

• The best sources of protein for vegan and vegetarian triathletes

Can protein make you poo?

So, all good. But what about this idea that protein can make you poo? Can it? Well yes, it possibly can, albeit more likely it’s the source of the protein than the protein itself that’s upsetting your tummy.

If you look at that list of food sources again, you can see ‘beans’ and dairy (in the form of cheese, milk etc), which are common causes of extra gastro activity. Beans contain high levels of fibre, which is great for your digestive health but does result in extremely regular pooing.

As for dairy, it could be that you’re lactose intolerant. The lactose in dairy-based protein like cottage cheese and Greek yoghurt can crank up your digestive system, especially if you’re lactose intolerant.

Another reason could be down to your post-workout protein powder. Many powders contain sweeteners such as sorbitol, which add sweetness without adding sugar.

The problem is that artificial sweeteners like sorbitol can have a laxative effect if consumed in large quantities, which could be you if you’re a consistent and committed athlete. Have a look at your tub of protein powder and if it’s packed with artificial sweeteners, like sorbitol, look elsewhere for a more natural option.

At the other end of the digestive spectrum, there’s also a chance that too much protein can make you constipated. Filling up on protein can squeeze your hunger to such an extent that you simply don’t want to eat any more including high-fibre foods like bananas. Fibre’s vital for a smooth-running digestive system. Insufficient intake and your stool won’t bulk up, leading to constipation.

You can also become constipated if you’re really dehydrated. That’s because higher protein intake requires more water or fluid to help the kidneys do their job. Fail to take in sufficient fluids and, once again, your stools won’t bulk up as they should and you end up constipated.

One last thing while we’re on the digestive and protein theme: a protein shake can make you fart. However, again it’s down to additives, in this case additive sugars like xylitol, mannitol and fructose. They might help the flavour of your protein shake but they can cause havoc on your gut.