Low carb diets shorten your life unless you are mostly vegetarian, study suggests

Large scale study debunks 'cult of low carb' and shows moderate intake gives best chance of a long life but type of proteins and fats make big difference

Low carbohydrate diets that have grown in popularity across the UK, US and Europe may shorten your life, especially when meat and dairy products are the main substitute for starchy foods, a major study has found.

US research found people eating a moderate amount of carbohydrates (50-55 per cent of their daily calorie intake) had lower mortality rates than those who eat “low carb” meals – below 40 per cent of calories.

This was further confirmed with a review on dietary studies from around the world, spanning 432,000 people, which also confirmed the health risks of high carbohydrate diets common in less well-off countries. But experts said advocates of the “cult of low carb” would still contest the mounting evidence.

The study also found not all low carbohydrate diets are equal.

“These findings bring together several strands that have been controversial,” said Professor Walter Willett, an epidemiologist with the Harvard TH Chan School of Public Health and one of the study’s authors.

“Too much and too little carbohydrate can be harmful but what counts most is the type of fat, protein, and carbohydrate.”

Low carbohydrate advocates replace pastas, bread and other mealtime staples with additional protein and fats for energy. Popular forms include the Atkins plan and the “paleo diet”, which tries to emulate pre-agricultural diets, though strictness varies with some allowing dairy and others eschewing vegetables.

The healthiest low carbohydrate diet types in the study, published in the Lancet Public Health on Thursday, were those which used lots of vegetables, plant oils and pulses (lentils and beans) to replace starchy carbohydrates.

However across Europe and North America the most popular low carbohydrate dieters get most of their energy from fats and protein in meat, cheese, butters, milk which can increase risks of heart disease and cancers.

“Low carb diets that replace carbohydrates with protein or fat are gaining widespread popularity as a health and weight loss strategy,” said Dr Sara Seidelmann, a cardiology specialist at Brigham and Women’s Hospital.

“However, our data suggests that animal-based low carbohydrate diets, which are prevalent in North America and Europe, might be associated with shorter overall lifespan and should be discouraged.

“Instead, if one chooses to follow a low carbohydrate diet, then exchanging carbohydrates for more plant-based fats and proteins might actually promote healthy ageing in the long term.”

For the US part of the research they followed more than 15,000 Americans over a 25-year period and tracked their mortality – however experts pointed out diets and health can fluctuate markedly over this period.

Previous studies have suggested that low carbohydrate diets help with short-term weight loss and improve blood pressure, but with little clear information on the long-term effects and what makes the best diet.

Public Health England guidelines recommend getting 50 per cent of our calories from carbohydrates, but this shows they should mostly be high fibre, wholegrain foods, rather than things like sweet drinks or high sugar foods.

Independent experts praised the study for taking on the contentious “low carb” issue head on and coming up with a clear message. Professor Nita Forouhi, an epidemiologist from the University of Cambridge, said this amounts to: “Moderate carbohydrate intake, and not a low carb diet, is optimal for longevity.”

“Current guidelines have been criticised by those who favour low carb diets, largely based on short-term studies for weight loss or metabolic control in diabetes, but it is vital to consider long-term effects and to examine mortality, as this study did.”

She said the study, although observational, was thoroughly conducted and the only realistic way to understand diet effects without assigning people diets for a lifetime.

“No aspect of nutrition is so hotly contended on social media than the carb versus fat debate, despite the long-term evidence on health benefits firmly supporting the higher carb argument,” said Catherine Collins a registered NHS dietician. “Yet supporters of the cult of low carb high fat (LCHF) eating, itself based on a lifestyle choice and the flimsiest of evidence supporting benefit, will no doubt disagree with this newest research on the subject.”