If you’ve been following a low-carb or low-fat diet in the hope of shedding some extra kilos, you’d better make sure that what you’re eating is healthy, or you may be unknowingly shortening your life span, according to US and Chinese experts.

People have been cutting carbs and fat from their diets to lose weight for decades. But new research published in JAMA Internal Medicine which examined the health records of 37,000 people in the US found those on unhealthy low-carb or low-fat diets were more likely to die earlier than people who weren’t on a diet at all.

But it wasn’t all bad news for people who stick to a low-carb or low-fat diet, as the researchers found that people on healthy low-carb or low-fat diets were less likely to die than people who didn’t diet. So, both low-carb and low-fat diets may make you healthier, depending on the types of food you choose to eat.

Many health experts in the past have criticised low-carb diets and labelled them dangerous fads. Most recently, research suggested that the popular ketogenic (keto) diet could cause kidney problems.

The keto diet requires people to cut out foods such as bread, rice, potato and sugar-based products such as soft drinks, cakes, lollies and biscuits and instead load up on protein-rich, high-fat foods such as meat, dairy and oils. The idea is that the body uses fat as its biggest source of fuel, breaking it down into ketones in a process known as ketosis.

According to food scientist Dr Vincent Candrawinata, the increased portions of protein in the diet may result in higher levels of ketones, which has been linked to kidney failure.

“For most healthy people a high-protein diet generally isn’t harmful, particularly when followed for a short time, however studies have confirmed that there are significant risks of [following] a high-protein diet with carbohydrate restriction for the longer term,” he said. “Those with existing kidney issues are at higher risk.”

Another study found those who followed a low-carb diet, such as the popular Paleo diet, died an average of four years earlier than those with moderate intakes of carbohydrates.

The study, published in The Lancet Public Health, followed 15,428 adults aged between 45 and 64 over two decades from 1987. The results showed that from age 50, the average life expectancy for those with moderate carbohydrate intake was four years longer than those who consumed very low levels of carbohydrates.