Can a low-carb diet help your heart health?

Overweight people on fewer carbs and more fat at lower risk of cardiovascular disease

Going on a low-carb diet has long been a popular weight-loss strategy. But some doctors and nutrition experts have advised against doing so over fears that it could increase the risk of heart disease, as such diets typically involve eating lots of saturated fats, the kind found in red meat and butter.

But a new study, one of the largest and most rigorous trials of the subject to date, suggests that eating a diet low in carbohydrates and higher in fats may be beneficial for your cardiovascular health if you are overweight.

The new study, which was published in the American Journal of Clinical Nutrition, found that overweight and obese people who increased their fat intake and lowered the amount of refined carbohydrates in their diet – while still eating fibre-rich foods like fresh fruits, vegetables, nuts, beans and lentils – had greater improvements in their cardiovascular-disease risk factors than those who followed a similar diet that was lower in fat and higher in carbs. Even people who replaced “healthy” wholegrain carbs like brown rice and wholewheat bread with foods higher in fat showed striking improvements in a variety of metabolic-disease risk factors.

The study suggests that eating fewer processed carbs while eating more fat can be good for your heart health, says Dr Dariush Mozaffarian, a cardiologist and dean of the Friedman school of nutrition science and policy at Tufts University, in Massachusetts, who was not involved with the research. "I think this is an important study," he says. Many people "still believe that low-fat foods are healthier for them, and this trial shows that, at least for these outcomes, the high-fat, low-carb group did better".


The new study included 164 overweight and obese adults, mostly women, and took part in two phases

“It’s a well-controlled trial that shows that eating lower carb and more saturated fat is actually good for you, as long as you have plenty of unsaturated fats and you’re mostly eating a Mediterranean-type diet,” Mozaffarian adds. Many doctors recommend a traditional Mediterranean-style diet, rich in fruits and vegetables, fish and heart-healthy fats like nuts and olive oil, for cardiovascular health. Other rigorous studies have found that following a Mediterranean diet can help to ward off heart attacks and strokes.

The new study included 164 overweight and obese adults, mostly women, and took part in two phases. First, the participants were put on strict low-calorie diets that lowered their body weights by about 12 per cent. Then they were each assigned to follow one of three diets in which 20, 40 or 60 per cent of their calories came from carbohydrates.

Protein was kept steady at 20 per cent of calories in each diet, with the remaining calories coming from fat. The participants were fed just enough calories to keep their weights stable. The participants followed the eating plans for five months, with all of their meals provided to ensure that they stuck to their diets.

In the United States, people get about 50 per cent of their daily calories from carbs, most of them in the form of highly processed starchy foods like pastries, bread and doughnuts and sugary foods and beverages. In the new study, the low-carb group ate significantly fewer carbs than the average American. But they were not on a super-low-carb ketogenic diet, which severely restricts carbs to less than 10 per cent of daily calories and forces the body to burn fat rather than carbohydrates. Nor did they eat unlimited amounts of foods high in saturated fats, like bacon, butter and steak.

Instead, the researchers designed what they considered practical and relatively healthy diets for each group. All of the participants ate meals like vegetable omelettes, chicken burritos with black beans, vegetarian chili, cauliflower soup, toasted lentil salads and grilled salmon. But the high-carb group also ate foods like wholewheat bread, brown rice, multigrain English muffins, strawberry jam, pasta, fat-free milk and vanilla yogurt. The low-carb group skipped the bread, rice and fruit spreads and sugary yogurts. Instead, their meals contained more high-fat ingredients, such as whole milk, cream, butter, guacamole, olive oil, almonds, peanuts, pecans and macadamia nuts, and soft cheeses.

After five months, people on the low-carb diet did not experience any detrimental changes in their cholesterol levels, despite getting 21 per cent of their daily calories from saturated fat. That amount is more than double what the US government’s dietary guidelines recommend. Their LDL cholesterol, the so-called bad kind, for example, stayed about the same as those who followed the high-carb diet, who got just 7 per cent of their daily calories from saturated fat. Tests also showed that the low-carb group had a roughly 15 per cent reduction in their levels of lipoprotein(a), a fatty particle in the blood that is strongly linked to the development of heart disease and strokes.

Mozaffarian says his take-home message for people is to adopt what he calls a high-fat Mediterranean-style diet

The low-carb group also had improvements in metabolic measures linked to the development of type 2 diabetes. The researchers assessed their lipoprotein insulin resistance scores, a measure of insulin resistance that looks at the size and concentration of cholesterol-carrying molecules in the blood. Large studies have found that people with high scores are more likely to develop diabetes. In the new study, people on the low-carb diet had their scores drop by 15 per cent – reducing their diabetes risk – while those on the high-carb diet had their scores rise by 10 per cent. People on the moderate carb diet had no change in their scores.

The low-carb group had other improvements as well. They had a drop in their triglycerides, a type of fat in the blood that is linked to heart attacks and strokes. And they had increases in their levels of adiponectin, a hormone that helps to lower inflammation and make cells more sensitive to insulin, which is a good thing. High levels of body-wide inflammation are linked to a range of age-related illnesses, including heart disease and diabetes.

Mozaffarian says his take-home message for people is to adopt what he calls a high-fat Mediterranean-style diet. It entails eating fewer highly processed carbs and sugary foods and focusing on fruits, vegetables, nuts, seeds, fish, cheese, olive oil and fermented dairy products like yogurt and kefir. "That's the diet" that people should be focusing on, he says. "It's where all the science is converging." – This article originally appeared in The New York Times