One year later, the high-fat, low-carb group had lost three times as much weight – 12 pounds compared with four – and that weight loss came from body fat, while the low-fat group lost muscle. Even more persuasive were the results of blood tests meant to measure the risk of heart disease and diabetes. The high-fat group, despite eating nearly twice as much saturated fat, still saw greater improvements in LDL cholesterol, HDL cholesterol, and triglycerides. This was enough to improve their scores on the Framingham Risk Calculator, a tool for predicting 10-year risk of heart attack. The low-fat group, by contrast, saw no improvement on their Framingham scores. “I think the explanation lies in how the low-fat dieters filled the hole left by fat – they just ate more carbs,” says Bazanno.
How a fatty pork chop can trump pasta begins with the fact that our bodies don’t process calories from fat, protein, and carbohydrates in the same way. “When we eat carbs, they break down into sugar in the blood; that’s true of whole grains, too, though to a lesser extent,” says Jeff Volek, a leading low-carb researcher at Ohio State University. The body responds with the hormone insulin, which converts the extra blood sugar into fatty acids stored in the body fat around our middles. Our blood sugar then falls, and that body fat releases the fatty acids to burn as fuel. But carb-heavy diets keep insulin so high that those fatty acids aren’t released, Volek says. The body continues to shuttle sugar into our fat cells – packing on the pounds – but we never burn it. Dietary fat, meanwhile, is the only macronutrient that has no effect on insulin or blood sugar. “This means it’s likely excessive carbs, not fat, that plump us up,” he adds. Low-carb diets stop that vicious cycle, keeping insulin levels low enough to force the body to burn fat again.
But isn’t too much saturated fat bad for your heart? “The evidence for that has really disintegrated,” says Dr. Eric Westman, a bariatric physician and director of the Duke Lifestyle Medicine Clinic. It is true that saturated fat can raise cholesterol. But as we know, there is good cholesterol and bad cholesterol. And it turns out that a diet rich in saturated fat increases the former while decreasing the latter. Carbs, on the other hand, do exactly the opposite. In fact, a new Annals of Internal Medicine review of 72 studies and hundreds of thousands of subjects found no strong evidence that saturated fat causes heart disease.
You know scientists are starting to get sure of something when they start to use terms like, “The evidence for that has really disintegrated.”
Now, the real question is how long it is going to take for your average family doctor to finally let go of last generation’s fat based folklore…Read more