The dangers of too much protein

The hunger for protein is insatiable. Up to half of adults increased their protein intake last year, according to a national poll, while searches for high-protein foods on Ocado’s website have doubled since 2023.

If you’re looking for the ultimate protein-rich, muscle-building food – eggs are the ultimate option but recently cottage cheese, once associated with bland diets, has enjoyed a 97 per cent increase in demand thanks to its high protein, low fat content. Increasingly dominant is the protein label creep smattered all over the packaging of everything from yogurts to ice creams and even some confectionary, such as high-protein versions of Snickers and Mars.

The global protein bar market is projected to grow from £3.71 billion in 2022 to £5.6 billion by 2029, according to Fortune Business Insights.

As consumers wise up to the additives and fat content of many popular processed bars such as the tough-sounding Grenade Oreo bar which contains more fat than a Mars Bar, the next generation of “cleaner” protein snack products are gaining popularity. Roam, for example, produces a range of additive and preservative-free meat bars using grass-fed beef, free-range turkey and pork.

According to polling company Savanta, people are increasingly consuming protein in the belief it helps them stay healthy, increases their energy levels and keeps them fuller for longer, rather than purely for muscle building purposes.

What’s clear is that we’re in the grips of protein mania and many of us, men especially, are eating it at the exclusion of all else, egged on by macho celebrities like Joe Rogan and even former vegan Bear Grylls, who now eats mostly meat. It’s not unusual for protein fans to eat as many as many as 56 egg whites a day. But while the benefits of protein are well-reported, is it possible to have too much of a good thing?

How much protein do we really need?

Clare Thornton-Wood is a registered dietitian and spokesperson for the British Dietetic Association. She says that most average sized adults get enough protein from their normal diet.

“The recommendation is that most people need 0.75g of protein per kilogram of body weight,” she says. “Anyone over 50, however, should aim to consume around 1g per kilogram of body weight because absorption decreases with age. Anyone doing muscle strength building exercise should aim for between 1.2g and 2g per kg of bodyweight.”

This means a 12st person (male UK average) should be aiming for 57g of protein a day and a 10st person (female UK average) should be aiming for 48g. Recommendations vary slightly to the US, where the recommended daily allowance is 0.8g per kilogram of body weight.

According to The British Nutrition Foundation, on average in the UK men eat about 85g and women about 67g of protein a day.

How to get the right balance?

A normal healthy diet with protein spread between meals should be adequate. For example, a breakfast of porridge with milk provides around 14g of protein, a tuna and sweetcorn sandwich with half a tin of tuna and seeded bread provides 26g, and a chicken breast with vegetables for dinner provides 35g. A snack of a handful of nuts provides an additional 7g of protein.

“You also get additional small amounts throughout the day from vegetables, milk in hot drinks, and even from snacks like chocolate and biscuits,” adds Thornton-Wood.

Indeed, many people taking supplemented forms of protein, such as shakes and bars, may be wasting their time and money, as the body cannot store protein. Instead, the protein is broken down into amino acids which are excreted if not used, or in the case of high protein diets the body converts excess protein to glucose which is stored as fat.

“If you’re going all out on having everything enriched with or fortified with protein and are not very active or doing a lot of strength and muscle building then you may be getting too much for your body to utilise, and it will pass out down the toilet,” says Thornton-Wood.

What are the risks of eating too much?

Protein is an essential nutrient found throughout the body, not just in muscle but in bone, skin, hair, and every other tissue. It makes up the enzymes that create biochemical reactions and the haemoglobin that carries oxygen in blood.

There are few risks of having too much protein per se. Indeed, an analysis by Harvard University which followed 130,000 people for up to 32 years, found that the percentage of calories from total protein intake was not related to overall mortality or to specific causes of death.

Instead, research indicates that the form the protein comes in (the protein package) rather than the amount is more likely to make a difference to health. For example, a high protein diet which relies on red meat may also contain high levels of saturated fat, while a diet reliant on powders and bars will likely include a lot of processed ingredients.

Inflammation

Researchers at the University of Navarra in Spain reported that certain animal-based sources of protein could cause higher levels of inflammation than foods like legumes, nuts, and beans. They found that obese people on diets who got more of their protein from meat had higher levels of inflammation compared to participants who consumed mostly fish or plant-based sources of protein.

However, another study of 2,061 participants found that overall inflammation and oxidative stress increased less in those with the highest protein intake than in those with the lowest. The study concluded that dietary protein, particularly from plant sources, may be associated with beneficial changes in the inflammatory burden in ageing populations.

Heart problems

Research conducted at the Harvard T.H. Chan School of Public Health, part of Harvard University, found that eating regular small amounts of red meat, especially processed red meat, is linked to an increased risk of heart disease and stroke, and the risk of dying from cardiovascular disease or any other cause. Another 2010 study analysed data on the dietary habits and health outcomes of 84,136 women and concluded that high red meat intake increases risk of coronary heart disease (CHD) and that the risk may be reduced by changing to other sources of protein.

Bowel cancer

Once again, the culprit is not volume, but the type of protein being consumed.

As Thornton-Wood explains: “Bowel cancer is linked to overconsumption of red meat and to consumption of too much processed meat.”

In 2015, the WHO’s International Agency for Research on Cancer concluded that consumption of processed meat is carcinogenic and that consumption of red meat is “probably carcinogenic to humans”. Thornton-Woods adds that eating protein at the expense of other nutritious foods like the fruit, vegetables, and whole grains, may also carry risks.

“Your gut biome will likely be less diverse. And we know that having a good, healthy, diverse gut biome is beneficial in terms of preventing cancer,” she says.

Data also shows positive associations between processed meat consumption and stomach cancer. It also shows the link between red meat consumption and pancreatic, prostate cancer, and breast cancer if excess red meat is consumed during adolescence.

High temperatures grilling can also create carcinogenic compounds on red meat.

Kidney failure

When protein is consumed, it is broken down into amino acids which are then used to build and repair tissue. This process produces waste products such as urea and urinary calcium, which must be filtered out of the blood by the kidneys. This can put a strain on the kidneys causing a range of problems including kidney stones and kidney failure.

A 2020 review published in the Journal of the American Society of Nephrology warned that high protein diets could damage renal function and cause a range of conditions leading to chronic kidney disease and permanent kidney damage in people both with and without prior kidney problems. The quality of dietary protein may also play a role. Animal protein has been associated with an increased risk of end-stage kidney disease in several observational studies.

“Eating excess protein does potentially put strain on your kidneys, particularly if you have a kidney condition. And as you get older, your kidneys are less efficient,” adds Thornton-Wood.

Diabetes

Eating more red meat can put you at a higher risk of Type 2 diabetes, while consuming nuts, legumes, and poultry is related to lower risk.

Constipation

The link between constipation and excessive protein consumption remains inconclusive, but there is evidence that diets where protein replaces other nutrients, particularly fibre and carbohydrates, can cause gastrointestinal (GI) problems. A 2024 paper, for example, concluded that dietary protein intake is not associated with stool consistency or frequency-defined constipation unless there is associated low carbohydrate intake, which can affect stool consistency.

Bloating and diarrhoea

People who consume excess amounts of protein powders, shakes and bars can be prone to bloating, flatulence and diarrhoea. These GI symptoms are generally caused by ingredients in products called sugar alcohols, also known as polyols. These sweeteners are not fully absorbed in the small intestine, which can lead to digestive upset when consumed in excess.

There is some evidence to suggest that keto diets can also create GI symptoms. A study in mice found that a high-fat, high-protein diet altered the structure of lactase-producing bacteria in the intestinal contents, which was likely to cause diarrhoea.

The protein danger zone: How much is too much?

There is no definitive answer, and detrimental protein intake depends largely on the type of protein being consumed. However, according to Dr Howard LeWine, a practising internist at Brigham and Women’s Hospital in Boston, for the average healthy person who is not an athlete or bodybuilder, “it’s probably best” to keep total protein intake to no more than 2g per kilogram of bodyweight. This equates to 128g or more a day for a ten stone person and 152g daily for a 12st person, equivalent to around four to four-and-a-half chicken breasts a day.