Low-carb, high-fat diet may improve heart health, study says

Going on a low-carb diet has been a common strategy for losing weight. But some doctors and nutrition experts have advised against doing so for fear that it could increase the risk of heart disease, as these diets — called “low-carb” in English — often include eating lots of saturated fats, the kind found in red meat and butter.

But a 2021 study, one of the largest and most rigorous ever done on the subject, suggests that a low-carb, high-fat diet may be beneficial for cardiovascular health if a person is overweight.

The new study, published in the American Journal of Clinical Nutrition, found that overweight and obese people who increased their fat intake and reduced the amount of refined carbohydrates in their diet — and ate high-fiber foods like fresh fruits, vegetables, nuts , beans and lentils – reduced their risk factors for cardiovascular disease more than those who followed a similar diet, but with less fat and more carbohydrates.

Even people who replaced “healthy” carbohydrates like brown rice and whole-grain bread with higher-fat foods showed impressive improvements in several risk factors for metabolic disease.

The study suggests that eating fewer processed carbohydrates and more fat may be good for heart health, said Dariush Mozaffarian, a cardiologist and dean of the Friedman School of Nutrition Science and Policy at Tufts University, who was not involved in the research.

“I think this study is important,” he said. “Most Americans still believe that low-fat foods are healthier, and this study shows that, at least for these results, the high-fat, low-carb group fared better.”

“It’s a well-controlled study that shows that eating less carbs and more saturated fat is actually good for people as long as they have a lot of unsaturated fats and are eating mostly a Mediterranean-type diet,” added Mozaffarian.

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 concluded that following a Mediterranean diet can help prevent heart attacks and strokes.

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

Protein was held steady at 20% of calories in both diets, with the remaining calories coming from fat. Participants were fed just enough calories to keep their weights steady. They followed the eating plans for five months, with all meals provided to ensure they followed the diets.

The average American gets about 50% of their daily calories from carbohydrates, most of them in the form of highly processed starchy foods like cakes, breads and doughnuts, and sugary foods and drinks.

In the new study, the low-carb group consumed significantly less carbs than the average American. But they didn’t go on a super-low-carb ketogenic diet, which severely restricts carbs to less than 10% of daily calories and forces the body to burn fat instead of carbs. Nor did they eat unlimited amounts of foods high in saturated fats, such as bacon, butter, and beef.

Instead, the researchers created what they considered practical and relatively healthy diets for each group. All participants had meals such as vegetable omelets, chicken pancakes with black beans, marinated roast beef, spicy beans, cauliflower soup, roasted lentil salad and grilled salmon. But the high-carb group also ate foods like whole grain bread, brown rice, multigrain English muffins, strawberry jam, pasta, low-fat milk and vanilla yogurt.

The low-carb group did not eat bread, rice, fruit jam and sugary yogurts. Instead, their meals included more high-fat ingredients such as whole milk, cream, butter, guacamole, olive oil, almonds, peanuts, pecans and macadamia nuts, and curd.

After five months, people on the low-carb diet did not experience any harmful changes in their cholesterol levels, despite getting 21% of their daily calories from saturated fat.

This amount is more than double what is recommended in the US government’s dietary guidelines. Their LDL cholesterol, the so-called “bad”, for example, remained about the same as those on the high-carb diet, who ate only 7% of their daily calories from saturated fat.

Tests also showed that the low-carb group had an approximately 15% reduction in levels of lipoprotein(a), a fatty particle in the blood that is strongly linked to the development of heart disease and stroke.

The low-carb group also had improvements in metabolic measures linked to the development of type 2 diabetes. The researchers evaluated their scores on lipoprotein insulin resistance, which looks at the size and concentration of cholesterol-carrying molecules in the blood.

Large studies have found that people with high LPIR scores are more likely to develop diabetes. In this research, people on the low-carb diet had their LPIR scores lowered by 15% — lowering their risk of diabetes — while those on the high-carb diet had 10% higher scores. People on the moderate carbohydrate diet had no changes in their LPIR score.

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

The study cost $12 million and was largely funded by the Nutrition Science Initiative, a nonprofit research group. It was also supported by grants from the National Institutes of Health, New Balance Foundation and others.

Mozaffarian said his message to people is to adopt what he calls a high-fat Mediterranean diet. This 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 people should focus on,” he said. “That’s where all the science is pointing.”

Translated by Luiz Roberto M. Gonçalves