What If Low Carb Diets Can Cure Diabetes And Heart Diseases
Following a low-carb diet has long been a popular strategy for losing weight. But some doctors and nutrition experts have advised against it, fearing that it could increase the risk of heart disease, since this type of diet usually involves eating a lot of saturated fats, such as those found in red meat and butter.
But a new study, one of the largest and most rigorous trials conducted on the subject to date, suggests that a low-carb, high-fat diet can benefit your cardiovascular health if you are overweight.
The new study, published in the American Journal of Clinical Nutrition, found that overweight or obese people who increased their fat intake and reduced the number of refined carbohydrates in their diet while continuing to eat fiber-rich foods such as fresh fruits, vegetables, nuts, beans and lentils-had greater improvements in their risk factors for cardiovascular disease than those who ate a similar, lower-fat, higher-carbohydrate diet. Even those who replaced "healthy" whole grain carbohydrates such as brown rice and whole wheat bread with high-fat foods showed striking improvements in various risk factors for metabolic diseases.
According to Dr. 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, the study suggests that eating fewer processed carbohydrates while consuming more fat may be beneficial for heart health. "I think this is an important study," he said. "Most Americans still believe that low-fat foods are healthier for them, and this trial shows that at least for these results, the high-fat and low-carb group had better results."
Still, Dr. Mozaffarian pointed out that the types and balance of fats you eat also seem to be important. People on a low-carb diet ate foods like butter, red meat, and whole milk, which are high in saturated fat. But most of the fats in their diet - about two-thirds-were unsaturated, the type of fat found mainly in olive oil, avocados, nuts, seeds, and fish.
"This is a well-controlled trial that shows that eating fewer carbohydrates and more saturated fats is actually good for you, as long as you eat a lot of unsaturated fats and follow a Mediterranean-style diet," Dr. Mozaffarian added. Many doctors recommend a traditional Mediterranean-style diet, rich in fruits and vegetables, fish, and heart-healthy fats such as nuts and olive oil, for cardiovascular health. Other rigorous studies have shown that following a Mediterranean diet can help prevent heart attacks and strokes.
The new study involved 164 overweight and obese adults, mostly women, and was conducted in two phases. In the first phase, the participants were subjected to a strict low-calorie diet that reduced their weight by about 12%. Then each was assigned to one of three diets in which 20%, 40% or 60% of calories came from carbohydrates.
Protein was kept at 20% of the calories in each diet, with the remaining calories coming from fat. The participants received just enough calories to maintain their weight stability. Participants followed the diets for five months, with all meals provided to ensure they adhered to their diet.
The average American gets about 50% of their daily calories from carbohydrates, mostly in the form of highly processed starchy foods such as pastries, bread and donuts, as well as sugary foods and drinks. In the new study, the low-carb group ate significantly fewer carbohydrates than the average American. But they were not on a very low-carb ketogenic diet, which severely limits carbohydrates to less than 10% of daily calories and forces the body to burn fat rather than carbohydrates. They also didn't eat unlimited amounts of foods high in saturated fat like bacon, butter, and steak.
Instead, the researchers designed what they considered to be convenient and relatively healthy diets for each group. All participants ate meals such as vegetable omelets, chicken burritos with black beans, seasoned London grill, vegetarian chili, cauliflower soup, roasted lentil salads, and grilled salmon. But the high-carb group also ate foods such as whole-grain bread, brown rice, multigrain English muffins, strawberry jam, pasta, skim milk, and vanilla yogurt. The low-carb group did not eat bread, rice, fruit spread, or sweetened yogurt. 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 a low-carb diet did not experience harmful changes in their cholesterol levels, although 21% of their daily calories come from saturated fat. This amount is more than double what the federal government's dietary guidelines recommend. Their levels of LDL cholesterol, the "bad" cholesterol, for example, remained about the same as those on the high-carb diet, where only 7 percent of their daily calories came from saturated fat. The tests also showed that the low-carb group had a reduction of about 15% in their lipoprotein(a) levels, a fatty particle in the blood that is strongly linked to the development of heart disease and stroke.
The low-carbohydrate group also saw improvements in metabolic measures related to the development of type 2 diabetes. The researchers assessed their lipoprotein insulin resistance score, or LPIR, a measure of insulin resistance that looks at the size and concentration of cholesterol-carrying molecules in the blood. Large studies have shown that people with high LPIR scores are more likely to develop diabetes. In the new study, people on a low-carb diet saw their LPIR score decrease by 15%, reducing their risk of diabetes, while people on a high-carb diet saw their score increase by 10%. Those on a moderate carbohydrate diet saw no change in their LPIR score.
The low-carb group also experienced other improvements. They had lower triglycerides, a type of fat in the blood that is linked to heart attacks and strokes. They also increased their adiponectin levels, a hormone that helps reduce inflammation and make cells more sensitive to insulin, which is a good thing. High levels of inflammation throughout the body are linked to a range of age-related diseases, including heart disease and diabetes.
The low-carb diet used in the study essentially eliminated highly processed and sugary foods while making room for "high-quality" carbohydrates from whole fruits and vegetables, beans, legumes, and other plants, said Dr. David Ludwig, one of the study authors and an endocrinologist at Harvard Medical School. "It's mainly about eliminating processed carbohydrates, which many people now recognize as one of the least healthy aspects of our diet," said Dr. Ludwig, co-director of the New Balance Foundation Obesity Prevention Center at Boston Children's Hospital.
Dr. Ludwig pointed out that the results do not apply to the very low carbohydrate levels typical of ketogenic diets, which have led to a significant increase in LDL cholesterol in some people. But he added that the study shows that people can get metabolic and cardiovascular benefits by replacing processed carbohydrates in their diet with fats, including saturated fats, without worsening their cholesterol levels.
The new study cost $12 million and was funded largely by the Nutrition Science Initiative, a nonprofit research group. He has also received grants from the National Institutes of Health, the New Balance Foundation, and others.
Linda Van Horn, a nutrition expert who served on the federal government's Dietary Guidelines Advisory Committee and was not involved in the new study, noted that the low-carb group consumed large amounts of unsaturated fats and fiber-rich vegetables, both of which are known to have beneficial effects on cholesterol and cardiovascular risk markers. The low-carb group, for example, consumed an average of 22 grams of fiber per day, which is higher than the average American intake, she said.
"Although the study is valuable and carefully designed, as always in nutrition research, there are many dietary factors that influence cardiometabolic risk factors that can help explain the results," said Dr. Van Horn, who is also chief of nutrition in the department of preventive medicine at Northwestern University Feinberg School of Medicine.
Dr. Mozaffarian said his take-home message for people is to adopt what he calls a high-fat Mediterranean diet. This involves eating less highly processed carbohydrates and sugary foods and focusing on fruits, vegetables, nuts, seeds, fish, cheese, olive oil, and fermented milk products like yogurt and kefir. "This is the regime that America should focus on. That's where all the science converges," he said.
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