My 22-year-old son has taken protein powder to fuel his hardcore workouts since he was a teenager. Bulky packets of white dust with names like “whey isolate” sit on top of our fridge and he’ll mix a scoop (containing about 27g protein) with water and down it before the gym. Protein bars are stacked up in the kitchen cupboard. He’s on trend — many of his friends take this “sports nutrition” too, like the fit-fluencers they follow on TikTok.
It’s a multibillion-pound industry, and sales continue to skyrocket. A survey this year suggested that people are spending an average of £2,208 on “healthy lifestyle” products — fuelled by Gen Z’s love of social media — with protein shakes the most widely used, consumed by 21 per cent of those surveyed. But do we actually know what these products are doing to their bodies?
This week the fitness expert Joe Wicks and Dr Chris van Tulleken, associate professor at University College London, health campaigner and author of Ultra-Processed People, joined forces to highlight not just how harmful and ubiquitous ultra-processed foods (UPFs) are, but how many are marketed under the “health halo” of being protein-enriched. Together they have created the “Killer” protein bar, which will be the subject of a Channel 4 documentary on Monday. It contains 96 ingredients, many of which are linked to cancer, stroke and early death, and all of which are entirely legal in the UK and commonly found in other products. Van Tulleken wrote this week that the bar they created was “the UK’s most dangerous health snack”.
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“Making a truly harmful protein bar is a way of showing how easy it is to put really unhealthy ingredients into a bar and sell it to you as a health food,” Wicks wrote. “Protein has become this thing that’s in everything — yoghurts, crisps, chocolate bars. But so many of them have additives, chemicals, sweeteners, gums, emulsifiers. A sandwich has probably got more nutrition than a protein bar. It’s basically all chemicals, just powders. There’s no food in it.”
They aren’t the first to raise concerns. This year Dr James Kinross, consultant colorectal surgeon at Imperial College London and author of Dark Matter, the New Science of the Microbiome, warned about the dangers of protein shakes, saying: “These protein powders are bad news and really bad for your gut.”
He notes: “Essentially, a very high-protein diet makes bacteria in the colon behave differently and not always in a good way. This is because some of the metabolites it produces are very toxic and we know that these cause harm or even cancer.”
The reaction — from some industry manufacturers and colleagues — was, he says, “a little hostile”. But he remains unrepentant.
“These powders are marketed egregiously to young people,” Kinross says. “We’re seeing a rapid rise in the use of these powders by teenagers — mostly boys — and twentysomethings.”
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Even if they look buff, he says, what about their insides? “Just because you’ve got lots of muscle, that doesn’t necessarily imply you’ve got a healthy gut,” Kinross says. And while existing research suggests protein powders are safe, he adds: “We just don’t have any good quality evidence for the long-term health consequences of protein powders taken by teenagers.”
Here he explains what parents need to know.
You can get all the protein you need from food
Banana oatmeal smoothies deliver high-quality protein, carbs and hydration
GETTY IMAGES
“We all need protein,” Kinross says. Amino acids are the building blocks of the human body and some are essential, meaning we can only get them from food, but many are actually eating too much of it.
My son favours tuna, eggs, chicken, beef — often eating meat twice daily: what in gym culture is called “gains-associated eating” (for bulking muscles) seen in those more likely to use protein supplements, Kinross says. Adults actually need roughly 0.75g protein per kilo of bodyweight a day. For the average adult man that’s 55g, or 45g for women, according to the Department of Health.
So what does that look like? A chicken breast contains about 45g protein, an egg about 6g, a 100g portion of Greek yoghurt about 10g, and — though there’s a fat chance of my son trying it — 100g cooked quinoa contains about 4g protein. If teens are particularly active, they could have up to 1g protein per kg of bodyweight a day, Kinross says, but anything over 1.5g/kg a day is considered a high-protein diet.
“You should only be eating this if you’re either an athlete, or this has been recommended by your doctor, eg for weight loss,” Kinross says. “More than 2g/kg per day consumed for long periods of time increases the risk of multiple adverse health effects, some of which include kidney stones, renal or liver injury, acne, altered mood, an irritable bowel, and possibly some types of cancer.”
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Too much protein can harm your gut
Protein is usually slowly digested in the stomach and small intestine over 3 to 6 hours, which is why it makes us feel full. But if you overeat protein — the average UK adult consumes about 76g daily before you add in any supplements, Kinross says — about 10 per cent reaches the colon where it’s fermented by bacteria.
“If we eat too much protein this fermentation produces molecules that can be harmful,” Kinross says. “Protein consumption increases the total number of bacteria in the gut, but it also influences the type — typically more clostridia and E. coli — and the functions of bugs which in turn make molecules — like ammonia, nitrosamines, or sulphides — which are quite toxic and damaging to the gut lining, causing inflammation and even cancer.”
There’s too much focus on protein — teens need more fibre
Dumping protein powder into a blender instead of eating a meal appeals to the teenager who finds “nutrition” confusing — or who can’t be bothered to heat up your bean chilli. “But packing your body with a powder is much, much less good for you than having a more natural food that has protein in the way your body needs to digest it,” Kinross says. “One of my other anxieties about too much focus on protein is the ‘fibre’ gap. The average person in the UK eats about 16g of fibre a day when we should be eating about 30g per day. We simply do not eat enough of this precious, plant-based food.” Just 7g per day more — there’s 2g in an apple — will reduce your risk of diseases like cancer, cardiovascular disease, diabetes and stroke. “It’s the cornerstone of a healthy diet,” he adds.
What are protein powders?
Protein from food is “a collection of lots of amino acids linked together folded into a molecule”, Kinross says. “Some powders are the whole protein and others are simple amino acids, just one of those building blocks in a refined powder.”
The king of protein powder supplements is whey, a protein derived from milk, and most frequently used by adolescents and adults who train. It can be bought as isolate (filtered from fats and carbs), concentrate (higher calorific content), and hydrolysed (readily absorbed and less likely to cause allergies), which reflect how processed it is. Another common milk protein is casein, which contains nine essential amino acids and is slowly digested. Increasingly popular is hydrolysed collagen — a connective tissue taken from the skin, bones and tendons of cows, pigs, chickens and fish, broken down into smaller peptides. Vegetable proteins — from peas (rich in branched-chain amino acids), soy, brown rice, sunflower and pumpkin seeds — are less popular.
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What about the longer-term effects of protein powders?
“These powders are very under-researched in young people,” Kinross says. “They’re classed as being safe by the FDA [the United States Food and Drug Administration] and other regulators. But there are very few high-quality studies looking at how these powders affect gut function and health in the longer term.”
He adds: “My critics in the supplement industry argue that the epidemiology doesn’t show a direct association between bowel cancer and protein supplements, therefore we shouldn’t worry. But I don’t think the science is robust, and given how excess protein interacts with the gut it worries me that young people’s consumption of it has so drastically and quickly increased.”
Is plant-based protein powder better?
My son is unlikely to quit protein powder entirely but, might it be worth encouraging him to stick to pea or soy? “Vegetable-based powders like pea and soy protein have a very different effect on the gut than whey and casein, animal-based protein,” Kinross says. Importantly, they contain a little fibre (pea protein contains 1-4g fibre per serving if minimally processed), and are more slowly digested. “They may also contain more isoflavones and other goodies, and they have a different relationship with the microbiome. For example, soy protein increases the abundance of beneficial microbes in the gut like bifidobacteria and akkermansia.” He adds: “They bulk your muscles at variable rates, but generally vegetable amino acids will be a little bit easier on the gut than animal amino acids.”
If you are going to buy them, ensure the powders and bars are additive-free
“Just like ultra-processed foods, a lot of these powders contain stabilisers to improve their longevity, and these additives can also cause harm,” Kinross says. “They interact with the gut and its microbes in ways we don’t yet properly understand, so if you take one, make sure there are no additional agents in it — no sweeteners, no emulsifiers, flavourings, thickeners.”
In one recent US analysis of 70 top-selling protein-powder brands, 47 per cent exceeded California safety thresholds for toxic metals, bisphenol-A (BPA, used to make plastic), pesticides, or other contaminants with links to cancer and other health conditions. “Worryingly, eating organic or vegetable [protein powders] was no better — on average. These showed higher levels of heavy metal contamination, with three times more lead and twice the amount of cadmium compared to non-organic products,” Kinross says. “Plant-based protein [powders] had three times more lead than whey-based alternatives, and chocolate-flavoured powders contained four times more lead than vanilla.”
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Make sure your teen knows what a healthy diet really is
Our society has a slightly warped view of what a healthy body looks like, Kinross says. “If you’re a young man, it’s this ripped, bulked, muscly body shape that places the emphasis on the outside rather than the health of the organs within. But if you’re hacking your body to achieve this, it’s likely you’re doing something unhealthy to your gut to achieve it.”
He adds: “Have a conversation about what a healthy, balanced diet really looks like. If they’re serious about their health, there’s a counter-narrative to the ‘powder-hacking’ — such as the importance of fibre in your diet, and having a varied diet that minimises UPFs and which contains carbohydrate and protein from both animal and vegetable sources with nuts, berries and a little fermented food. For most of us, the massive overconsumption of an individual macronutrient like protein is rarely healthy.”
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If my son remains hellbent on taking protein powder, he should mix it into a real-food milkshake, not stir it into water, Kinross says. “Put it into the healthy shake because that provides some of the other food matrix you really need to protect the gut a little bit more.” Even better, ditch it entirely and, pre or post-workout, whizz up a banana smoothie, which delivers high-quality protein, carbs and hydration: try 300-400ml of milk, a banana, 2.5 tablespoons of Greek yoghurt, a teaspoon of honey, a handful of oats or scoop of nut butter. “Depending on the milk or yoghurt used, it contains around 18-22g protein,” Kinross says. Meal-wise, he says, chicken, rice and loads of vegetables pre-workout will serve him better than a powder or bar.