What protein bars do to your gut, heart and waist

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When TV presenter Joe Wicks decided to create a parody version of a common ultra-processed food, or UPF, for a new Channel 4 documentary, it didn’t take him long to conclude that a protein bar was the obvious choice.

For, as noted by Chris van Tulleken, Wicks’ co-presenter on the documentary and one of the UK’s best-known experts on UPFs, protein bars are “the ultimate UPF.”

“They’re an example of a UPF that is purely predatory, really,” van Tulleken told The Telegraph.

“They really aren’t food; they are mixtures of industrial chemicals. They often have no real ingredients, and they’re discretionary and expensive. They are the product with the greatest gap, in my view, in terms of how healthy they claim to be and how unhealthy they really are.”

As depicted in the resulting film Joe Wicks: Licensed to Kill, Wicks and van Tulleken team up to create the Killer protein bar, which, just like many standard bars, is brimming with additives.

As the Killer bar’s website states, it contains the commonly used sweetener aspartame, which is classed as “potentially carcinogenic” by the World Health Organisation, the sugar alcohol xylitol, which has been associated with a higher risk of cardiovascular disease, and the emulsifier carboxymethylcellulose, which may promote gut inflammation. Consuming it regularly would likely be detrimental to your long-term health.

While the bar is high in calories, sugar and saturated fat, it also contains 19g of protein and 27 vitamins and minerals. According to van Tulleken, the point of this stunt is to highlight how many food companies are able to create essentially unhealthy products but still make nutritional and health claims because they’ve added protein and vitamins.

What’s in a Killer bar?

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How unhealthy ultra-processed foods can be marketed as healthy

The point of the Killer bar is to try to pressurise the Government into tightening existing lax regulations, which make it possible for such a bar to be sold commercially. For example, while the UK has a so-called front-of-pack traffic light system, with red colours indicating if a product is deemed high in fat, sugar, or salt, it is entirely voluntary and requires manufacturers to choose to opt in.

“The insanity is that traffic lights are voluntary,” says van Tulleken. “In some cases where there would be a red traffic light, they just leave the traffic lights off. So it just doesn’t work.”

Such an exposé is particularly timely because of the sheer size of the protein bar industry. Some estimates have suggested that in two years’ time, the global protein bar market will be worth more than £5bn.

In the eyes of many nutrition researchers, its success is built on something of a myth, perpetuated by claims from both the food industry and a growing array of self-identified health experts on social media, that many of us are deficient in dietary protein, and the more we can get, the better.

Instead, the majority of us are actually getting plenty of protein through our diet alone, while the evidence for the commonly cited claim that high-protein diets can help with weight loss is distinctly mixed. In reality, while research does suggest that protein can be more satiating than carbohydrate and fat, longer-term studies haven’t always found that people lose more weight on high-protein diets compared with other weight-loss diets.

“It’s a marketing ploy and it’s been hugely successful, to the extent that masses of people believe that instinctively it must be true,” says Michael Lean, professor of human nutrition at the University of Glasgow. “And so there’s a huge machine now selling protein bars, shakes, and high-protein everything.”

Instead, as highlighted by Wicks and van Tulleken, there are plenty of reasons why the typical protein bar in stores isn’t very good for you.

Let’s take a look at some of the main ones.

1. They could disrupt your gut

As Lean points out, if you were to consume pure whey protein, one of the most common protein sources in protein bars, it would taste somewhat nasty. As a result, most bars are flavoured with either added sugar or various sweeteners, and sometimes both.

While regulators have repeatedly approved various commercial sweeteners as safe, some studies have flagged concerns. According to NutriNet-Santé, a major epidemiological study in France involving data from more than 100,000 people, those who consume more artificial sweeteners have a higher risk of cardiovascular diseases.

A handful of preclinical investigations and small clinical trials have indicated that some artificial sweeteners, like neotame, can damage gut cells in petri dishes, and that others, such as saccharin, sucralose, and aspartame, may alter the gut microbiome, although this research is far from conclusive.

Eugenia Hamshaw, a clinical nutritionist at the Icahn School of Medicine at Mount Sinai, notes that some protein bars branded as “low sugar” contain 18 grams of polyols, a class of sweetener otherwise known as sugar alcohols. “They’re putting them in so they can say, ‘We deliver on protein without a lot of sugar,’” she says.

The downside, however, is that for some people, polyols can cause significant digestive symptoms, particularly those who are prone to irritable bowel syndrome, bloating, or general gut issues. “If you’re someone who tends to have a sensitive digestive system, these ingredients might not be your friend,” says Hamshaw.

2. They could contribute to raising your cholesterol levels

To create an appealing taste and texture, many protein bars use readily available and low-cost fats such as coconut or palm oil. As a result, it’s not uncommon for bars to contain between five and eight grams of saturated fat, which is considered high.

The NHS points out that, over time, consuming too much saturated fat can raise your cholesterol levels and increase your risk of heart disease, and suggests daily limits of 20 grams of saturated fat for the average woman and 30 grams for the average man.

However, this means a single protein bar could take up somewhere between 25 and 40 per cent of those limits. “It’s kind of a lot for a snack,” says Hamshaw. “It feels substantial to me.”

3. You might not get much benefit from the protein

While most people consume these bars with the aim of upping their protein intake, a study published earlier this year by Hungarian food scientists revealed that many bars are not even that effective in offering a useful source of dietary protein.

In the study, László Abrankó, a professor at the Hungarian University of Agriculture and Life Sciences, and his colleagues reviewed more than 1,600 protein bars on the market and reached two conclusions. Firstly, a number of bars use collagen as a protein source, which he describes as a “low-quality” protein from a nutritional sense, as it doesn’t contain all the amino acids that the body requires.

“You won’t retain it in your body, as you can’t utilise it,” he says. “So you’ll just excrete it.”

Secondly, even when protein bars do use high-quality protein sources such as milk, soy, or quinoa, this protein isn’t necessarily digestible in the protein bar format. Abrankó and his colleagues examined this by simulating the process of human digestion in the lab, using test tubes containing digestive enzymes and various shakers and incubators to replicate peristalsis and intestinal motility.

At the end of the process, they found that digestibility scores ranged from a reasonable 81 per cent to just 47 per cent in the case of some bars.

Abrankó believes that the artificial structure of the protein bar, which meshes protein with other ingredients such as gels, fats, and sometimes fibre, impacts the body’s ability to break it down and access the important amino acids.

4. They could increase your risk of heart disease

Protein bars use food additives known as emulsifiers to blend their varying ingredients together. Common choices are soy lecithin and carrageenan, which are popular for their gelling and stabilising properties. The problem is that, just like saturated fat, consuming more emulsifiers, such as lecithins, has been linked to a heightened risk of cardiovascular disease in a large population study.

Like sweeteners, emulsifiers have been approved as safe by food regulators, but epidemiologists remain concerned. Another population study reported an association between higher intake of carrageenans and some cancers and type 2 diabetes, although, as with lecithins and cardiovascular disease, a causative link has yet to be established.

Hamshaw says that while the science is still unclear on the precise dangers of certain ingredients found in ultra-processed foods, one of the main issues with these foods is that they don’t provide the same synergy when it comes to lots of nutrients working together at the same time as whole foods.

“Think about having a Greek yogurt with some nuts and berries,” she says.

“You’re getting fibre from the fruit, healthy unsaturated fatty acids from the nuts, and protein and calcium from the yogurt. That’s not happening in foods that have been manipulated to have a nutrition label look a certain way, like protein bars where we’re using polyols to keep the sugar down and protein powders to up the protein.”

5. They could lead to weight gain

Being ultra-processed foods, protein bars are also relatively calorie-dense compared with whole food snacks, typically containing somewhere between 200 and 400 calories. That’s as much as a chocolate bar, and in many cases more. A 51g Mars bar contains approximately 228 calories, while a standard two-finger milk chocolate KitKat bar contains 104 calories.

When researchers at Arizona State University (ASU) carried out a small clinical trial in 2023 to assess the consequences of eating them on a daily basis, they found that protein bars increased overall dietary calorie intake to the extent that participants saw a 3 per cent increase in body fat in just a week.

“That was just in a week,” says Carol Johnson, an ASU professor who led the trial. “Imagine if you carried that on for five, six, seven weeks.”

Hamshaw says this is a particularly important point, as one of the main reasons why people are turning to protein supplements and bars is the hope of losing weight. “It’s important to understand that just because it’s a protein bar, that doesn’t mean it’s low calorie,” she says. “If you’re trying to reduce your overall calorie intake, it might not be the most optimal choice for you.”

6. They could lead you to overeat

The protein content within bars is a mixture of purified powders, known as protein isolates, and hydrolysed proteins, which have been reduced to their constituent amino acids. As with many ultra-processed foods, which are often blends of powders and pastes, because the protein has been so heavily broken down, consuming it is unlikely to be satiating, making you more prone to eating more and overconsuming.

“That’s my main concern,” says Hamshaw.

“It’s not necessarily all that filling, so you might end up being hungry again an hour or two later. In that case, you need to ask yourself, what is this really doing for me? If the goal is to tide you over between meals and it’s not satiating, you have to ask yourself how much it’s really of benefit to you.”

Essentially, as Lean concludes, the overwhelming commercial success of protein bars, more than anything, is tantamount to the sheer effectiveness of modern commercial marketing.

“We’re basically persuading people that it is normal to eat things our grandparents wouldn’t have recognised as edible,” he says

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