A low-carb diet can increase your risk of mortality by up to 38% each year

Low-carb diets can increase your risk of mortality by up to 38%, a new study finds.

Participants were split into two groups, comparing those who ate the least carbs with those who ate the most carbs – and it turns out cutting them out isn't a good idea for your long-term health.

Meanwhile, a low-fat diet, another popular choice for those aiming to lose weight or boost their fitness, is shown to reduce your risk of early death each year by up to 34%.

A low-carb diet might include cutting out sugars, bread and starchy veg, and eating meat, eggs, dairy and leafy veg instead, while a low-fat diet might focus on fruit and veg, lean meats and cutting out fatty oils.

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Researchers categorised people as eating either a 'healthy' or 'unhealthy' low-fat or low-carb diet, depending on whether they got their food from 'high' or 'low' quality sources.

They found that eating a low-carb diet showed patterns contributing to an early death, with people on keto-style diets 28% more likely to die from any cause, compared to those eating high-carb diets.

Participants on an 'unhealthy' low-carb diet increased their mortality risk by 38% each year.

However, those on a low-fat diet, regardless of whether this was 'healthy' or 'unhealthy', reduced their likelihood of an early death compared to those on high-fat diets. The risk of dying from any cause each year was down 21% on any type of low-fat diet, and down 34% on a healthy one.

Specifically, low-fat diets were associated with a lower cardiovascular mortality of 16% and lower cancer mortality of 18%.

The findings – published in the Journal of Internal Medicine – are based on research from Harvard University and Tulane University in the US and Chinese scientists. They looked at data of 371,159 participants aged 50 to 71 dating back to the 1990s, analysing the links between diet and length of life.

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What are healthy carbs?

Contrary to common belief, healthy carbs include starchy foods like potatoes, bread, rice, pasta, and cereals, eaten wholegrain where possible (or with the skin on for potatoes) – you just need to watch out for the way you cook them. Unhealthy carbs are found in sweets, sweetened drinks, ice cream and plain sugar, among other things.

Similarly, while most fats are considered unhealthy, there are some unsaturated fats we should be having, which may include avocados, some nuts, fish and olive oil.

Why do we need healthy carbs?

Starchy foods are our main source of carbohydrate, and should make up just over a third of the food you eat, according to the Eatwell Guide.

"Complex, slowly digestible carbohydrates, often referred to as the 'healthy' carbohydrates, are usually rich in fibre, vitamins and minerals [such as calcium, iron and B vitamins] which are all vital for our health and wellbeing," explains Lifesum’s lead nutritionist Signe Svanfeldt.

"Unhealthy carbs, however, often contain very few (or no) other nutrients, which means they don’t provide our body with anything other than just pure energy and a quick blood sugar raise."

While some people think all starchy foods are fattening, gram for gram they actually contain fewer than half the calories of fat, according to the NHS. Just try to avoid any added fats from when you cook and serve them, as this will increase calorie content.

Honing in on the benefits of fibre found in 'healthy' carbs like whole grains, legumes, root veg and fruit, Svanfeldt says, "Fibre is important for our digestive health, and supports our microbiome (which is linked to a variety of bodily functions such as our immune system and mental health).

"Fibre can also support weight maintenance since it helps us stay fuller for longer. Eating according to the recommended 30 grams of fibre per day has also shown to decrease the risk of heart disease."

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Why is eliminating healthy carbs bad for you?

Cutting out any food group, unless you have a medical reason to, isn't healthy or sustainable.

"If you eliminate foods that contain healthy carbs from your diet, the first sign you most likely will notice is that your digestive tract will react and lead to less functioning bowel movements," says Svanfeldt. "An unbalanced diet can also lead to nutrient deficiencies, which can lead to a variety of unwanted symptoms such as hair loss, bone weakness, fatigue and dizziness."

Excluding certain food groups may also lead you to eat more of something else, like replacing carbs with foods rich in saturated fats like butter, coming with additional consequences.

"This can increase the risk of heart disease, or if the carbs are replaced by red meat, the risk of bowel cancer increases," says Svanfeldt. "So the key is to find a balance of nutritious foods that provide our bodies with a sufficient amount of healthy nutrients to support its functions."

A healthy diet typically consists of eating fruit and veg, high-fibre starchy foods, dairy or dairy alternatives, protein, unsaturated oils and spreads, and plenty of fluids.

If you have any health conditions, speak to your doctor or health professional about what diet is best for you.

Watch: Greg Wallace explains how healthy eating instead of dieting helped him lose weight