What is a low-carb diet and is it healthy?

Dietary regimes that are both low and high in carbohydrates could shorten life expectancy by up to four years, according to a new study.

Low-carb diets have become “increasingly popular” for weight loss, the BBC writes. They have also shown promise in “lowering the risk” of some illnesses.

But in a report published in the Lancet Public Health journal, researchers at Brigham and Women’s Hospital in Boston, Massachusetts, found that these diets can also have negative consequences, shortening people’s lifespans by up to four years.

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The report also found that a high-carb diet, which The Guardian reports is “common in Asian and poorer nations where people eat a lot of refined carbohydrates such as white rice”, has similiarly adverse effects. Such diets can reduce lifespans by an average of one year.

But what does a low-carb diet consist of? And what do we know about its effect on weight loss and health?

What is a low-carb diet?

Low-carb diets, such as the controversial Atkins diet and the ketogenic diet, involve drastically reducing the intake of carbohydrates primarily found in sugary foods, pasta and bread.

This includes cutting back on grains, starchy vegetables and fruit, and making up the calorie deficit with foods high in protein and fat, such as meat, fish and dairy products.

Is a low-carb diet good for you?

In terms of slimming down, certainly, but such diets could have other perks, according to some experts. “A low-carb diet is generally used for losing weight,” the Mayo Clinic says, but some low-carb diets may have health benefits “beyond weight loss,” such as reducing risk factors associated with type 2 diabetes and metabolic syndrome.

Not all scientists agree that low-carb diets are entirely good news. The Lancet study found that consuming less than 40% of calories from carbohydrates carried a higher risk of mortality, although a definite cause has not yet been identified.

Such diets can also mean different things to different people. The Guardian reports that “not all low-carb diets are equal”, and that people who adhered to low-carb diets often ate fewer vegetables and plant-based proteins and fats, instead opting for meat and fats such as lamb, chicken, steak, butter and cheese.

Researchers noted that some of those animal products have been linked to the stimulation of oxidative stress, inflammatory pathways and biological aging – and could shorten lifespans.

The study concluded that eating a moderate amount of carbohydrates is best for a healthy lifespan. Those who do opt for a low-carbohydrate diet should consume plenty of vegetables, plant oils and pulses (lentils and beans) in order to replace starchy carbohydrates, rather than consuming excessive amounts of meat and fat.

“These findings bring together several strands that have been controversial,” said co-author Walter Willett. “Too much and too little carbohydrate can be harmful but what counts most is the type of fat, protein and carbohydrate.”