Does protein deserve its hero status? Photo / DepositPhotos
We’re being inundated with protein. There’s more to the muscle mass and weight loss equation.
First, they came for fat. Then carbs. But in a world of shifting dietary villains, protein has won the macronutrient war of attrition.
And won it big. In an annual survey done by the International Food Information Council, a group funded primarily by the food industry, consumers this year reported that “good source of protein” was their top criterion for healthful food, edging out “fresh” and “low in sugar” for the first time.
Here, for your eating pleasure, is a primer on the macronutrient that – in a pleasant change – nobody seems to hate.
Protein is necessary for human life. Fat and carbohydrates are our primary fuel, but protein literally builds us. Forty-two per cent of our body weight (not counting water) is protein. It’s our muscles, but also hair, skin and fingernails. (There’s a great explanation of this in Food Intelligence, a new book by scientist Kevin Hall and journalist Julia Belluz).
The key is nitrogen, which is essential to building amino acids, the constituent parts of proteins. Plants get nitrogen from soil, and we get it by eating plants or other animals that eat plants. Without it, we can’t exist.
It’s hard to know exactly how much protein we need, but we have a decent ballpark. How much protein should I eat? It’s a simple question. But, like other nutrition questions that sound simple, it’s hard to answer. And all the questions are hard for the same reason: humans are difficult to study.
Scientists can tell you exactly how much protein rats need, because they can keep rats captive for their entire lives, feed different groups different amounts of protein, and see which ones survive. In human studies, that’s frowned upon.
I asked Kevin Klatt, a nutrition researcher who’s on the board of the American Journal of Clinical Nutrition, how we go about figuring out human protein requirements. “Nitrogen balance studies,” he told me. Because we’re turning over proteins all the time – they get damaged or oxidised or used as fuel – we need to take in enough nitrogen to rebuild what we lose.
Sounds straightforward, but it’s hard to do. “You have to keep people locked up, you’re sweeping the floor to get the skin cells, you’re collecting pee and poop and hair,” Klatt said.
Based on those studies, most recommendation bodies conclude that 0.8g of protein per kg of body weight is an adequate amount, although there’s evidence that 1.2g per kg helps retain muscle mass in older people. (A different method, called the indicator amino acid oxidation method, which Klatt says is not universally agreed upon, comes up with slightly higher results for adults, and levels up to 2.1g per kg for athletes, but that’s a deep dive for another day.)
For the average male in the United States, who weighs about 90kg, 0.8g per kg is 73g of protein, nearly 300 calories – about 10 to 15% of caloric requirements. If you’re trying to picture that in food, an egg has 6g of protein, a cup of cooked lentils has 18g, and four ounces of sirloin steak has 25g.
Higher levels of protein don’t help with long-term weight loss. Eating more protein for weight loss is a popular idea, but it doesn’t pan out in trials. While there might be a small advantage in the short term (a few months), it disappears in the long term.
Take any diet, and you’ll find some people who make it work for them. And if it’s working for you, mazel tov! Weight loss, and weight maintenance, are hard, and we should use any tool that helps. What you should not be doing is insisting that, because a specific diet works for you, it’s the key to weight loss for everyone. It’s not.
There are many, many studies – so many that we even have many meta-analyses – of how protein affects muscle mass. If you read through them, you find that most find a small benefit from increased protein intake when coupled with resistance training. But some find no effect at all. One meta-analysis from 2018 found that protein supplementation did increase muscle mass and strength, but only up to 1.62g per kg of body weight per day. A more recent study put the upper limit at 1.1g/kg. Beyond that, you just pee it out.
The same is true of creatine, a compound composed of three amino acids, often sold as a supplement for bodybuilders. It can help with building muscle, but it needs to be consumed in conjunction with weight training.
“Doing the resistance training is 90% of the battle, if not 99%,” Klatt told me. “And extra protein is a slight boost.”
But, as with just about every nutrition issue, evidence is inconsistent. It depends on the population group (older people? women? athletes?), the level of protein the people are starting with, the kind of exercise they do, and the outcomes being measured. Not to mention the kind of protein they consume! Is it dietary or supplements? Is it from plants or animals? And the levels of total protein intake, including both supplement and dietary intake, are often not specified at all.
Very high protein levels may increase the risk of heart disease. There is some evidence that a diet high in protein can raise heart-disease risk, both in humans and animals. Although observational research generally doesn’t find a link between high-protein diets and cardiovascular risk, few people in the wild reach the level that researchers are concerned about: 40% of calories from protein. (And, of course, the usual caveats about observational research still apply: humans can’t report their diets accurately, and people who eat a lot of protein are different from people who eat little in ways that have nothing to do with diet.)
Generally, animal protein is more readily available for use by your body than plant protein, and some studies have found it to be better for building muscle mass. My favourite study on protein source, though, comes from the beef industry, which pitted an omnivorous diet against a vegan one with the same amount of protein, and found no difference in muscle fibre protein synthesis after nine days of resistance training. Hey, if the beef industry says it doesn’t matter, who’s going to argue?
Wait, don’t answer that.
Klatt points out that supplements are different. Once the protein is isolated, it’s readily absorbed by the body, and even food processing that breaks down whole plants can make protein more bioavailable. “You’ll absorb more protein from chickpea pasta than from whole chickpeas,” he told me.
You’re probably eating more than enough protein. As with all consumption statistics, it’s difficult to get accurate numbers, but the best estimate we have of meat consumption (which is from the meat available in the US, rather than what’s actually eaten) comes from the Food and Agriculture Organisation of the United Nations, and has Americans averaging about 200g of meat per day . And that doesn’t count eggs, dairy or plant protein, so most of us are doing just fine.
But the most important thing to remember about protein is none of those things. It’s that, beyond the necessary minimum, it doesn’t matter very much. Lots of folks are trying to amp up protein’s hero status, usually because they have a supplement, or a book, or a theory to sell. And they get traction, in part because they’re giving people an excuse to eat more meat, a food most people enjoy. Don’t fall for it.
Humans are astonishingly adaptable omnivores, and we can thrive on a wide range of diets, with a wide range of protein content. Pick the one you enjoy, that helps you accomplish your goals, and, most importantly, the one that you can stick with.