Fat, carbs, and protein. You’ll have heard of these three macronutrients before. But which is truly critical to your diet?
Answer: all of them. Together, they’re essential for keeping your body functioning; they give you energy and make sure all your cells are working properly.
However, you’d be forgiven for thinking that protein is more essential than the others – and that you’re not getting enough of it.
After all, why else would food companies have quadrupled the amount of high-protein products available worldwide over the past decade, with the investment in such produce expected to rise almost eight per cent every year until at least 2028?
What could the motive be for squeezing protein into everything from snack bars, breakfast cereals and drinks to pasta, yoghurts and much, much more?
Quite simply, protein sells. The food industry’s high-protein drive is sadly not all part of a public health plan to fix a hidden diet deficiency in society. In fact, while many of us (including half of Americans) are aiming to increase our daily protein intake, most of us are already eating too much of it.
How much you really need
Protein is, of course, incredibly important to our bodies. Made up of long chains of molecules known as amino acids, it is protein’s job to repair cells in our bodies, particularly after exercising.
“Our muscles are rapidly turning over tissue. Every 60 days, all the proteins in our muscle are broken down and rebuilt,” says Graeme Close, professor of human physiology at Liverpool John Moores University.
“Protein is important in our immune cells, skin, biological enzymes – a huge number of processes. If we’re not consuming enough, we can become deficient in any of these areas.”
Found in high quantities in foods like cheese, fish, meat, eggs, beans and legumes, the World Health Organization recommends healthy adults eat 0.8g of protein per kg (0.01oz per lb) of their body weight every day. That means a person weighing 80kg (176lb) needs about 64g (2.3oz) of protein a day – about two chicken breasts.
However, you’re unlikely to only eat two chicken breasts in a day. Protein can also be found in smaller quantities in the likes of pasta (roughly 3g/0.1oz per serving), milk (8g/0.3oz per cup) and peas (8g/0.3oz per cup) – all of which adds up.
Considering this, it’s little wonder men and women are eating, on average, 81g (2.9oz) of protein per day. For most people, this is at least 20 per cent beyond recommendations.
But it’s worth noting there are some groups that will require more protein than others. For instance, it’s recommended malnourished patients eat between 1.2–1.5g per kg (0.02oz per lb) per day.
Similarly, those aged over 65 also need to increase their intake to between 1.2 and 2g per kg (0.02–0.03oz per lb) of weight per day to help maintain all-important muscle.
“It’s inevitable that we start to lose muscle as we get older, and this can lead to reduced mobility, strength, independence, and quality of life,” says Dr Oliver Witard, reader of exercise metabolism and nutrition at Kings College London. “When it comes to how much protein we need, context is key.”
But what if you regularly exercise or are even a professional athlete? Surely you’ve got good reason to reach for a supplement? Probably not. While athletes are often advised to have high-protein diets, this often just means eating more foods overall, not solely protein drinks.
“Athletes generally perform a lot of physical activity, which means they also need to consume a lot of food to ensure they stay in energy balance,” says Luc van Loon, professor of physiology of exercise and nutrition at Maastricht University Medical Centre in the Netherlands. “Therefore, most already consume a lot of protein in their diet, which means that they generally don’t need to add more.”
In short, unless you’re above 65, or have special circumstances, you’re probably getting more than your fair share. Protein deficiency isn’t the problem here, but a surplus probably is.
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An excess of protein
What happens if you consume too much protein? Let’s be clear: there’s actually little evidence that too much protein can lead to serious issues you might associate with veiny bodybuilders. For instance, a high-protein diet has been linked to compromising kidney function, but only for people with underlying problems, according to Witard.
However, there are real issues with increasing the ratio of protein in your diet, particularly if you’re extremely active. “For athletes, the main risk associated with increasing protein intake is that this means compromising other macronutrients,” Witard says.
“If it’s at the cost of carbohydrates, this could be counterproductive in a period of intense training.”
For the rest of us, there’s one big risk in eating too much protein: weight gain. Protein, after all, is still calories. And any excess protein you don’t use is simply stored as fat.
True, eating an excess of protein may not be as bad for you as eating the same amount of carbohydrates. As one meta-review found, protein appears to have a ‘protective effect’ against weight gain when a person is consuming excess calories – especially when this is combined with weight training.
However, the full impact of this effect isn’t yet clear. And, as van Loon argues, overconsuming any macronutrient is likely to cause you problems.
“Overeating – eating more calories than you’re burning – increases the chance of developing chronic metabolic diseases,” explains van Loon. This, in turn, greatly increases your risk of obesity.
In other words, unlike what the washboard abs displayed on supplement packets suggest, eating more high-protein foods could well lead you to develop more belly fat than muscle.
The source matters
So far, so worrying. But obesity may be the least of your woes depending on how you source your protein.
“While there’s no definite link between overall protein intake and risk of death, greater intake of animal protein is associated with a higher risk of death. And plant protein is associated with a lower risk,” says Walter Willett, professor of epidemiology and nutrition at Harvard TH Chan School of Public Health, in the US.
As Willett explains, this is largely because of the saturated fat and cholesterol that’s found in animal (and thus meat) cells. Plants, however, contain more unsaturated fats, fibre and healthy phytochemicals such as flavonoids.
This means that going ‘full caveman’ and ramping up your red meat consumption is likely to greatly increase the risk of cardiovascular disease and reduce your life expectancy – especially if all those sirloin steaks are replacing whole grains and healthy plant oils in your normal diet.
But what about the clichéd stereotype of the ‘weedy vegetarian’? Surely meat is a better source than plants for building muscle? Not necessarily. Although past research suggested animal protein tends to be better digested due to differences in its structure, recent studies have indicated plant-based sources of protein are by no means inferior.
Indeed, a review of studies in 2021 concluded there's little difference, in terms of muscle strength or lean body mass between animal and plant protein – however, those on a plant-based diet generally have slightly leaner mass without fat.
“When it comes to building muscles and having an optimal immune response, it ultimately doesn’t seem to matter where your protein comes from,” Close says.
Due to the risk to your overall life expectancy, the best sources of protein, Close argues, are mostly plants – including nuts, beans and other soy foods, and whole grains. However, he still recommends getting your protein from a range of foods, including occasional fish, poultry and dairy products.
(Pro tip: if you’re interested in maximising muscle growth, scientists recommend consuming protein throughout your day, across a minimum of four meals.)
However, if you rely solely on plant proteins and want to grow any muscle, there is one catch: you need to make sure your diet contains all the essential amino acids (the amino acids your body can’t produce on its own).
“Individual plant proteins are typically deficient in at least one of the nine essential amino acids, typically lysine or methionine. But, importantly, not both. You need them all to build muscle,” Witard says.
“Lysine is particularly important because it is both a signal and a substrate. Once lysine appears inside the muscle cell, it acts like a traffic light signal, and the proteins that control metabolism are switched on.”
This all means, Witard says, you need to ensure you’re consuming complementary plant-based protein sources to tally up your essential amino acid requirements. For instance, while lentils contain a lot of lysine, they aren’t a great source of methionine. Grains, such as oats, however, are a good source of methionine. Eat them both in a day and you’ll have a complete protein.
Other examples of complementary proteins to eat together include pasta with peas, black beans with rice, or whole-wheat bread with peanut butter.
By combining complementary proteins, to ensure you have all the amino acids covered, there’s no reason plant proteins can’t be as useful for muscle health and performance as animal protein, Willet says. And there are some plant proteins with higher levels of lysine than others, including maise, lentils, peas and quinoa.
What about protein supplements?
Of course, meat and grains aren’t the only sources of protein nowadays – there’s also a burgeoning market of bars and powders boasting an impressive amount of muscle fuel on the packet. However, don’t be too taken in.
“I’d much prefer people getting protein from natural sources,” Close says. “In my industry, we talk about the ‘whole-food approach’. And where this isn’t possible, that’s when you can look to a supplement.”
This isn’t just an expert being snobby. Ultimately, the likes of protein bars are often ultraprocessed foods, which have been associated with an increased risk of obesity due to being dense in calories and sneakily ramping up your appetite.
“But protein bars and shakes don’t need to be totally avoided if they’re made from healthy plant sources and not loaded with sugar,” Close adds.
“Sometimes they’re convenient, for example, on a long bike ride. And they’d usually be better than a bar or shake made mostly from refined starch and sugar. But again, most people don’t need them.”
From the perspective of a person’s whole diet, such products may only make up a small part of their daily protein intake, says van Loon – and what a person eats throughout the entire day is much more important.
“However, there are other ways to improve diet besides only taking protein supplements. You should only supplement on top of a good diet,” he says.
Overall, the occasional protein shake won’t do you much harm. Do it every day, however, and you might have a problem. You’ll be left consuming a horde of unneeded calories, with your bank balance slimming a lot faster than your waistline.
So relax: although the health industry wants you to think you have a serious diet deficiency – one that can only be solved by purchasing several expensive barrels of powder – your protein intake is (very likely) nothing to worry about.
About our experts
Prof Graeme Close is a Professor of Human Physiology at Liverpool John Moores University. He has been published in Nature Food, the International Journal of Sports Science & Coaching and Sports Medicine.
Dr Oliver Witard is a Reader in Exercise Metabolism and Nutrition at King's College London University. His work has been published in Human Nutrition & Metabolism, the European Journal of Clinical Nutrition and the International Journal of Sports Nutrition and Exercise Metabolism.
Prof Luc van Loon is a Professor of Physiology of Exercise and Nutrition at Maastricht University Medical Centre in the Netherlands. He has been published in the Journal of the Academy of Nutrition and Dietetics, The American Journal of Clinical Nutrition and The Journal of Physiology.
Prof Walter Willett is a Professor of Epidemiology and Nutrition at Harvard TH Chan School of Public Health, in the USA. His work has been published in Neurology, Diabetologia and The American Journal of Clinical Nutrition.
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