Can You Eat Too Much Protein?

Depending on who you ask, we're either eating "too much" protein, or we need protein shake after protein shake just to build a little muscle or lose weight. The truth isn't either of these. Some of us may need more, while others get more than enough — but more isn't necessarily harmful. Here's how to figure it all out. Illustration by Sam Woolley

More Than Enough Isn't 'Too Much'

Last time we talked about protein, we were trying to figure out how much was enough. To recap, the Health and Medicine Division of the National Academies says that 98 per cent of us will get enough protein if we eat 0.8g of protein per kilogram of body weight. That number, the RDA, is the basis of textbook and government guidelines. It works out to about 54g for the average woman, who is about 68kg, or 72g for the average man at about 91kg.

Most Americans eat more than that. In this report from the US Department of Agriculture, based on a large survey from 2010, men ate 98g of protein per day on average and women ate 68g. Protein intake was low in some older adults and some teenage girls, but most of us easily meet the textbook requirements.

Studies like that one have led to a sort-of myth that we are all eating "too much" protein. But that's misleading. It's more correct to say that on average we are eating more than enough protein. That's a good thing! After all, we wouldn't want to eat less than enough.

So that number we started with — 0.8 grams per kilogram — is a minimum. And it's only the minimum for people living an averagely sedentary life. If you exercise a lot, or if you're trying to lose weight, it makes sense to eat more than that.

Even if a marathon runner or a bodybuilder would be healthy with a protein intake near the textbook amount, they may be even healthier, or able to do better in their sport, with a higher intake. Again, that's not too much; it's within the range that their body can put to good use. This range goes up to 1.8g/kg, depending on the athlete and their sport. That's 123g for a 68kg person, or 164g for a 91kg person.

Extra Protein Just Means Extra Calories

You'll notice that even the higher levels we discussed are well under the 1g per pound (2.2g per kilogram) "rule" that bodybuilders and some other athletes like to repeat. You don't have to look far to find people who are trying to eat 200 or even 300g of protein in a day, on the theory that more is better. The extra protein won't hurt you, but it could make you gain weight.

Here's what's going on in your body. We eat protein so that we have amino acids (protein's building blocks) to build our own protein-containing body parts. That includes muscle as well as hair, skin, enzymes and all kinds of little components of our cells. But we only need so much. Eating an extra 100g of protein won't make your body decide to build 100 more grams of muscle and hair. Instead, that extra protein is just... food.

Just like we can burn fat or carbohydrates as fuel, we can burn protein. And just like we can convert those nutrients to fat for storage, we can do that with protein too. To burn or store protein's kilojoules, our body has to remove the nitrogen-containing "amino" part from each amino acid, and the most convenient way to excrete that nitrogen is in urine. That's given rise to a bizarre myth that it's impossible to eat too much protein because your body will "pee out the excess". No, the kilojoules from the protein are still being stored or burned like any other kilojoules. Your pee just contains an indicator of the fact that you ate some of your kilojoules in the form of protein.

That's disappointing if you're trying to lose weight: You could have had those same kilojoules in a different form that maybe you liked better. Perhaps a grilled cheese or a small dessert instead of an umpteenth dry chicken breast.

The 'Dangers' of High Protein Diets Are Overblown

The same US government document that lays out the recommendations for protein also contains a note about the "adverse effects of excessive consumption", There is no level of protein, it says, that is associated with adverse effects. Instead, they recommend that protein make up between 10 and 35 per cent of adults' kiloujoules. They chose the lower number to provide enough protein to meet the RDA, and the upper number is, basically, as much protein as you can eat while still getting the recommended fat and carbohydrate.

So if the National Academies don't think high protein intakes are dangerous, who does? Mainly people who aren't up on the science, and groups like the pro-vegetarian Physicians' Committee for Responsible Medicine. They list kidney disease, cancer and kidney stones as downsides of a high protein diet.

But we need to remember that protein is not the same thing as meat. High intake of red and processed meat is linked with cancer, but that's no reason to avoid other protein sources like chicken, tofu, beans or whey powder. The connection with kidney stones is iffy, too: Animal protein seems to be linked with stones, but the American College of Physicians couldn't find enough evidence to recommend low protein diets for people prone to stones.

And the idea that too much protein will "place a strain on your kidneys," as the PCRM says, has also been debunked. As Chris Kresser points out, people who have donated a kidney aren't at risk for kidney disease, even though their remaining kidney is working twice as hard. That makes the "strain" idea a tough sell. Low protein diets do help people who already have kidney disease, but there isn't any evidence that high protein is harmful for people who have healthy kidneys to start with.

Find Your Sweet Spot

Since there's no strict limit on protein for healthy people, you need to find out what is the right amount of protein for you. Use your activity level and goals (along with our guide) to figure out what your minimum should be. That's your "enough". Track what you eat to make sure you're getting an amount close to that. Tracking is especially helpful if you're on a restrictive diet, whether paleo or vegan or just very low kilojoule, since you might not realise what you're missing.

Then, to find your personal "too much", look at your kilojoules. Does 300g of protein (that's 5100kj) really fit into your diet? If you truly love the taste of tuna and protein shakes, it's not our business if you pig out. But if a high protein diet is more trouble and more kilojoules than it's worth, that's when it becomes too much.


Comments

    Does anyone else get a protein headache when eating too much protein in one sitting?

    So if the National Academies don’t think high protein intakes are dangerous, who does? Mainly people who aren’t up on the science, and groups like the pro-vegetarian Physicians’ Committee for Responsible Medicine. They list kidney disease, cancer and kidney stones as downsides of a high protein diet.

    bullshit. i once way over-did whey protein isolate powder, and i was diagnosed with renal (kidney) failure and osteo-arthritis. stopped the protein shakes and both conditions dissapeared without any other diet change.

    a quick google scholar search turns up agreeing articles:

    http://www.sciencedirect.com/science/article/pii/S0272638604012533
    http://www.sciencedirect.com/science/article/pii/S0272638602000392
    http://agris.fao.org/agris-search/search.do?recordID=US880447088

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