“Reducing calories, no matter the source, (whether) carbs or fats, is most important for weight loss overall”, said Lona Sandon, a dietician at the University of Texas Southwestern Medical Center at Dallas, in a statement on the study provided by the NIH. They said the study had “debunked” numerous claims that low-carbohydrate diets were better, but the long-term impact was still unclear.
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At the end of the two dieting periods, the researchers found that body fat lost with dietary fat restriction was greater compared with carbohydrate restriction, even though more fat was burned with the low-carb diet. The test group completed two, two week trials; one week they ate a low-carb diet and the following seven days they consumed less fat.
Scientists intensely analysed people on controlled diets by inspecting every morsel of food, minute of exercise and breath taken.
All the participants were obese and followed a balanced diet, and half of the participants reduced their calories by 30 percent by either following a low-carb or low-fat diet. Experts say the most effective diet is one people can stick to.It has been argued that restricting carbs is the best way to get rid of a “spare tyre” as it alters the body’s metabolism. During the second period the conditions were reversed. “While people may have been more excited to see greater weight loss with the carb restricted diet, most of this weight was from water, not fat”. Hall said that the findings counter the theory that body fat loss necessarily requires decreasing insulin, thereby increasing the release of stored fat from fat tissue and increasing the amount of fat burned by the body.
“All of those things do happen with carb reduction and you do lose body fat, but not as much as when you cut out the fat”, said lead researchers Dr Kevin Hall, from the US-based National Institute of Diabetes and Digestive and Kidney Diseases. However, over prolonged periods the model predicted that the body acts to minimize body fat differences between diets that are equal in calories but varying widely in their ratio of carbohydrate to fat.
Hall does caution against making sweeping conclusions about how to diet from this study.
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The researchers had previously simulated the study with a math model of human metabolism, whose body fat predictions matched the data later collected in the study. He felt that people had very strong opinions about what matters for weight loss and what particular diets to go by without having an actual physiological data as a basis for their beliefs. He hopes these results might inform why people respond differently to different diets.
