Why do you need protein?
Protein is necessary for human life. Fat and carbohydrates are our primary fuels, but protein literally builds us. 42% of our body weight (excluding water) is protein. It’s not just our muscles, it’s also our hair, skin and nails. (There’s a great explanation for this. food intelligenceA new book by scientist Kevin Hall and journalist Julia Belluz).
The key is nitrogen, which is essential for making amino acids, the building blocks of proteins. Plants obtain nitrogen from the soil. We get nitrogen by eating plants or other animals that eat plants. Without it we cannot exist.
How much protein should we consume?
It’s difficult to know exactly how much protein we need, but there are appropriate levels. How much protein should you eat? It’s a simple question. But like other seemingly simple nutrition questions, it’s difficult to answer. And all questions are difficult for the same reason. Humans are difficult to study.
Scientists know exactly how much protein mice need. That’s because you can keep mice captive for their entire lives, feed different groups different amounts of protein, and see which mice survive. In human research, that’s frowned upon.
I asked Kevin Klatt, nutritionist and director of the American Journal of Clinical Nutrition, how to determine a person’s protein needs. “Nitrogen balance studies,” he told me. Because we are replacing proteins all the time – they become damaged, oxidized or used as fuel – we need to consume enough nitrogen to rebuild what we have lost.
It may seem simple, but it’s difficult to execute. “You have to lock people up, sweep the floor to get skin cells, collect urine, feces and hair,” Klatt said.
Based on these studies, most recommending organizations conclude that 0.8 grams of protein per kilogram of body weight is an adequate amount for older adults, although there is evidence that 1.2 grams per kilogram helps maintain muscle mass. (Another method, called the Index Amino Acid Oxidation Method, which Klatt disagrees with universally, gives slightly higher results for adults and suggests levels of up to 2.1 grams per kg for athletes, but that’s a deep dive for another day.)
For the average American male weighing about 90 kg, 0.8 grams per kg corresponds to 73 grams of protein, which is equivalent to nearly 300 calories or about 10 to 15 percent of calorie requirements. If you think about protein in food, an egg has 6 grams of protein, a cup of cooked lentils has 18 grams, and a 4-ounce sirloin steak has 25 grams.
Does protein help with long-term weight loss?
Higher protein content does not help with long-term weight loss. Eating more protein to lose weight is a popular idea, but it doesn’t work out in trials. There may be some benefit in the short term (a few months), but it disappears in the long term.
No matter what diet you try, you’ll find people who do it for them. And if it helps you, mazel tov! Losing weight and maintaining it is difficult. So you should use whatever tools help you. What you shouldn’t do is claim that because a particular diet works for you, it’s the key to weight loss for everyone. That’s not true.
How does protein affect muscle mass?
There is a lot of research on how protein affects muscle mass. There are also too many meta-analyses. If you read this closely, you’ll see that most people will see small benefits from increasing their protein intake combined with resistance training. However, some people find it ineffective at all. A 2018 meta-analysis found that protein supplementation increased muscle mass and strength, but only up to 1.62 grams per kilogram of body weight per day. A more recent study set the upper limit at 1.1 g/kg. Other than that, you can just pee.
The same goes for creatine, a compound made up of three amino acids often sold as a supplement for bodybuilders. It can help build muscle, but should be taken in conjunction with weight training.
“Doing resistance training is 90%, if not 99%, of the battle,” Klatt said. “And the extra protein gives you a little boost.”
However, as with almost all nutritional issues, the evidence is inconsistent. This depends on the population group (older people, women, athletes?), the level of protein people start with, the type of exercise, and the outcome being measured. Not to mention the type of protein they consume! Is it a diet or a supplement? Does it come from plants or animals? And total protein intake, including supplements and dietary intake, is often not specified at all.
Is it dangerous to eat too much protein?
Very high protein levels may increase your risk of heart disease. There is evidence that diets high in protein may increase heart disease risk in both humans and animals. Observational studies generally do not find a link between high-protein diets and cardiovascular risk, but few people in the wild reach 40% of their calories, a level that concerns researchers. (And, of course, the usual caveats for observational studies still apply: Humans cannot accurately report their diets, and people who eat more protein differ from people who eat less in ways unrelated to diet.)
Which is better for building muscle mass: animal protein or plant protein?
Animal proteins are generally more readily available to the body than plant proteins, and some studies have shown them to be better for building muscle mass. But my favorite research on protein sources comes from the beef industry. The study compared omnivorous and vegan diets containing the same amount of protein and found no differences in myofibrillar protein synthesis after nine days of resistance training. Hey, who would argue if the beef industry said it didn’t matter?
Wait, don’t answer.
Klatt points out that supplements are different. Once proteins are isolated, they are easily absorbed by the body, and their bioavailability can also be increased through food processing that breaks down the entire plant. “You will absorb more protein from chickpea pasta than from whole chickpeas,” he said.
Does it really matter how much protein you eat?
You are probably eating more protein than you should. As with all consumption statistics, exact figures are difficult to obtain, but the best estimate of meat consumption (from meat available in the United States, not from actual meat eaten) comes from the Food and Agriculture Organization of the United Nations, which estimates that Americans eat an average of about 200 grams of meat per day. It doesn’t contain eggs, dairy, or plant-based proteins, so most of us are doing just fine.
But those aren’t the most important things to remember about protein. If you exceed the minimum amount required, it is not a big problem. Many people are trying to elevate protein’s heroic status. Usually because they have a supplement, book, or theory to sell. And they gain traction in part because they give people an excuse to eat more meat, a food most people enjoy. Don’t fall for it.
Humans are incredibly adaptable omnivores, able to thrive on a varied diet with varying protein content. Choose something you enjoy, something that will help you achieve your goals, and most importantly, something you can stick to.
