Is it unhealthy to cut out carbs?

For people struggling to lose weight, it’s an appealing notion: slash your carb intake to turn your body into a fat-burning machine. Yet scientific opinion about the importance of carbs is still divided.

Increasingly, research suggests that cutting back might be beneficial, especially to treat type-2 diabetes and obesity. But official dietary advice, such as from the NHS Choices website, continues to state that carbs should make up one third of our total diet (which adds up to half our total calories*). The public has good reason to be confused.

A bit of history

Low-carb diets are nothing new. In the mid-19th century, William Banting published a paper in The Lancet expounding the benefits of a low-carb/high-fat diet for weight loss. Cardiologist Dr Robert Atkins took up the baton in the 1970s, gaining millions of followers.

Since then the Atkins model has been repackaged as keto, LCHF (low-carb, high-fat) and Dukan, to name a few. The diet even found its own catchphrase: “No carbs before Marbs”, coined by stars of The Only Way is Essex, who cut back to lose weight before a trip to Marbella. Reducing carb intake lowers levels of insulin, the hormone that stimulates fat storage.

By doing this the body burns fat to use as energy rather than storing it, during which it also produces chemicals called ketones. A strict ketogenic diet, which generally involves eating less than 50g carbohydrate per day, should only be undertaken under medical supervision.

The case for carbs…

Carbs have been a cornerstone of official health advice for decades. Aisling Pigott, registered dietitian and British Dietetic Association spokesperson, says carbs are a key source of energy and nutrients, which also keep us feeling full. Cutting back on carbs may lead to deficiencies in fibre, calcium, iron and B vitamins, and may even cause weight gain caused by carb cravings.

“We don’t need to demonise carbohydrates, but instead think about the body’s needs,” Piggott says. People who are inactive or who want to lose weight might consider restricting pasta, rice and potatoes to a fistful. “It’s not helpful to remove carbohydrate from the diet completely,” Pigott concludes.

In 2015, an investigation by the Scientific Advisory Committee on Nutrition (SACN) said that half our calorie intake should be from carbs, finding “no association” between their intake and weight gain, type-2 diabetes or heart disease.

…and the case against

A recent study by the Prospective Urban Rural Epidemiology (PURE), published in The Lancet last year tracked the eating habits of 135,000 people in 18 countries over seven years. They found a significant increase in mortality among people on high-carbohydrate diets, and an association between high-fat intake and lower mortality. Critics argued that, although there appeared a link, there was no proof that carbs were responsible for the higher death rate. Moreover, an association between higher carb intake and mortality did not mean a lower carb intake had health benefits.

Some doctors argue that official dietary guidelines need rethinking. Emeritus Professor Iain Broom, former Director of the Centre for Obesity Research and Epidemiology at Aberdeen’s Robert Gordon University, says a pro-carb approach is based on the now-discredited theory that dietary fat is unhealthy. “If this continues, there’s no way the obesity and type-2 diabetes epidemic will be curtailed.”

Professor Broom encouraged his patients who had failed to lose weight or to control their type-2 diabetes to cut out potatoes, root vegetables, rice, pasta and foods with added sugar, and to limit fruit to two pieces per day. As his patients’ health improved, their carb intake was maintained at 100-150g per day. “This worked extremely well,” Prof Broom says.

One or two small studies have suggested that, for some people, low-carb diets may have an adverse effect on memory and cognitive ability, due to reduced glucose in the bloodstream. However, more research is needed on this.

The middle ground

Naveed Sattar, Professor of Cardiovascular and Medical Sciences at the University of Glasgow, says it’s important to remember that not all carbs are the same. Most of us would benefit from cutting back on refined carbs such as sugary drinks and snacks, white pasta and bread, especially people who regularly eat more than the recommended amount.

But starchy foods such as vegetables, wholegrain bread and fibre-rich cereals are good for us. “I would not change the official dietary advice for most people,” Prof Sattar says.

Cutting carbs may help weight loss in the short term. The evidence suggests that substituting carbs with protein – which makes us feel fuller sooner – leads people on this type of diet to take in fewer calories. However, low-carb diets are hard to stick to in the longer term. (It’s easy to forget, too, that many alcoholic drinks, including beer and wine – not spirits – contain carbs). “Low-carb diets may be an effective way of losing weight, but they are no better than others in the long run,” concludes Prof Sattar.

The bottom line

While emerging evidence suggests that low-carb diets may be useful for helping treat obesity and conditions such as type-2 diabetes, for most people carbohydrates are healthy, contain crucial nutrients and keep us feeling full.