High-protein or high-carb: Will either boost your fitness?

Whether you’re an occasional gym goer, exercise enthusiast or professional athlete, you’ve probably received tips on how changing your diet could boost your fitness. You might be tempted by high-protein products to build strength, or to reduce your carb intake in order to improve performance. Or the opposite, you might consider ‘carb loading’ before a sporting event and consuming further carbs during the event in the hope they’ll fuel and power you through.

Advice for diets aimed at supporting exercise often falls into one of these two camps:

• Low carb + fat + protein – to help build and repair muscle while burning fat
• Carb-led + low fat – to give you the energy to perform well without taking on extra fat.

But is one really better than the other?

How much protein and carbohydrate should we consume?

“Dietary guidelines recommend around half our daily calorie intake (one-third of the food you eat) should come from carbohydrates – these are found in starchy foods, such as bread, pasta, rice, couscous, potatoes, breakfast cereals, oats and other grains like rye and barley.

“Wholegrain or higher-fibre varieties should be chosen where possible,” says nutrition scientist and British Nutrition Foundation spokesperson, Sarah Coe.

As for protein? “Adults need around 0.75g protein per kilogram of body weight per day. If you are regularly active, you may need slightly more protein to help with muscle growth and repair,” says Coe.

However, as you’d imagine, things start to change when you’re a sports professional.

“The exact amount of carbohydrate or protein an athlete needs varies individually, depending on their sport, training programme, and intensity and duration of exercise sessions.

An athlete training for three to five hours per week is recommended to have 4–5g carbohydrate per kilogram of body weight per day, whereas an athlete who trains much more intensively for at least two hours a day will need double this amount.

“The protein requirements of strength and endurance athletes are higher than those of the general population. Strength athletes typically require 1.2–1.7g protein per kilogram of body weight per day, whereas endurance athletes need 1.2–1.4g protein per kilogram of body weight per day,” she says. This is because protein contains amino acids, which are the building blocks for muscle growth.

The recommended dietary differences between athletes and well, everyone else, is something Dr Michael Newell, Sport and exercise nutrition lecturer at University of Westminster, discusses.

“They’re the physiological weirdos of this world,” says the School of Life Sciences professor. He isn’t being critical of the world’s leading endurance athletes, in fact the opposite. He’s explaining how, when it comes to elite performers and their diet, often their biological make-up is different from that of the rest of us.

“Endurance athletes have been selected for the sport because they’re very good at it and also because they are exceptionally good at consuming high rates of carbohydrates – those two things need to go together. You don’t get an elite marathon runner who can’t consume carbohydrates at a high rate,” he says.

Dr Michael highlights record-breaking marathon runner Eliud Kipchoge as an example of a person’s physiology being different from the grand majority of others. “His aim was to consume around 90g of carbohydrate per hour (during a marathon). Most people would be violently sick if they tried to do that.”

As Coe says, prescribed amounts of protein and carbohydrate can differ depending on the person’s sport and weight. This inevitably means diets differ, even within the same sport.

While professional athletes have nutritional advice prescribed to them and their physiological make-up examined in great detail, this probably isn’t something the average gym-goer will have access to. Which can lead to problems…

Alexandra Cook is a competitive endurance runner and sports dietitian. Rather than suggesting clients take on extreme diets that either focus on carbs or protein, she prefers a more balanced approach.

“There’s a huge amount of misinformation out there. We’re in a world where there are a lot of influencers and people tend to look at what other people are doing and think, ‘if it’s worked for you, it’s going to work for me’,” she says.

Cook finds herself having to battle misinformation about certain diets – especially ones that are restrictive. “Some athletes – especially in the ultra-endurance world – do tend to go for this low-carb approach and it works for them, which is great. But then they say ‘when I’m up and running, I’ve never felt fitter’.

“That doesn’t mean it’s going to work for everybody else. I know for sure if I cut out carbohydrates, I probably wouldn’t be able to get out of bed, let alone run a 50-mile race.”

So Cook’s approach is to instead tweak the guidelines to the individual she’s working with, “so that it accounts for their sport or for personal reasons such as different tastes and requirements.”

This means no extremes of either protein or carbs.

This balanced approach is something Dr Newell agrees with. “If you want to be able to train consistently, it would be ridiculous to exclude any macro-nutrient, in my opinion. To put it simply, you need carbohydrates to sustain longer, high-intensity training, and you need protein to help recover from that and to replace amino acids you’ve lost. On top of that, you need a bit of fat in order to ensure you get an adequate number of calories in your diet.

“This isn’t particularly exciting or novel, it’s the Eatwell Guide advice. There’s a tendency for the newest-best-thing to be the diet you should be doing. But actually, there’s usually limited evidence behind whether they are attainable and have the results people think they do,” he concludes.

“Protein is a big sports nutrition product at the moment, so I encourage people to look at who’s pushing it and why. Of course, protein is a very important nutrient, it’s vital for helping us perform and get the best out of ourselves,” says Cook.

“It also helps us repair and recover. But currently people are being led to think they need an extortionate amount. The reality is, if we take on more protein than our body needs, we’ll just excrete it out.

The sports dietitian continues: “Recently I kept a food diary, just out of interest, to see how much I was consuming. Without thinking, I was eating enough protein. This is simply because most people who train regularly eat a greater volume of food overall, so most reach their protein requirements and more without even trying.

“If you have a portion of protein at each meal, and if you’re doing slightly higher training loads you get protein from snacks like nuts, peanut butter and milk, you’ll easily meet your protein requirements.”

Coe also emphasises this point: “It’s a myth that eating lots of extra protein equals bigger muscles. While protein supplements are popular among some gym-goers for muscle building, they are generally unnecessary as most active people can easily get enough protein from a healthy, varied diet, including high-quality, lean protein foods.”

Tom Huelin is the fitness coach for football club Forest Green Rovers – the ‘world’s first 100 percent vegan football club’. As part of his responsibilities, he gives nutrition advice to the team.

While the players are in control of their own meals at home, at work they follow a vegan diet and there are “a lot of vegetarians and a couple of vegans” in the squad.

However, being a vegan club doesn’t make the nutritional requirements different from those of any other team. Tom explains that both protein and carbs in particular are a big focus for the footballers’ requirements. And the amounts prescribed depend on the football schedule.

“Football’s a results business, and the most important time to be nutritionally prepared is on match day. So you just start with that and work backwards into the training days to make sure you’re at your optimum on match day,” Huelin says, before explaining what each day needs to include.

The basics are: on the days they’re going to be working harder they consume more carbs, and they make sure after intensive sessions they receive a top-up of protein to help with muscular fatigue. To help encourage the team to receive the correct nutrition when they’re off the clock, they have access to an online resource which includes recipes for vegan meals.

“The vegan element of it is key. We can attribute lots of positive things to it – physically and in terms of the levels of recovery. Players are feeling less fatigued. These are anecdotal of course, so while it might be they get these effects from following (at least) a semi-plan-based diet, we don’t know for sure,” the fitness coach says.

Is it a challenge to get all the right nutrients into the players on a vegan diet? “No, and that’s because there are now good vegan plant protein supplements. It wasn’t always the case. When I first joined the club, I found it really tricky to get something that had a sufficient amount – and the right type – of protein.

“In the last four years though, as veganism has become fashionable, more and more sports nutrition brands are developing vegan protein products. And we use things like soy milk, which is really high in protein.”

So will one diet improve your fitness levels?

Kind of. While there’s research to support the view that low-carb diets could help athletes, there’s also plenty pointing to the opposite, that low-carb diets will inhibit exercise performance.

Does that mean carbs win the race? They’ll definitely give you the fuel you need to compete, but you do need protein with comprehensive amino acids to repair and help build your lean muscle mass.

The experts we spoke to all advocate that it’s preferable to not cut any macro-nutrients out of your diet and to follow healthy eating guidelines – adapting them depending on your individual demands rather than re-writing them entirely.

So, combined protein, carbohydrate and even fat should all help you cross that finish line – but unless you’re an elite athlete, you’ll almost certainly get enough of these from a healthy diet.

*Originally published January 2020. Updated April 2025

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