Cutting dietary fat led to 68% more body fat loss than cutting the same number of carbohydrate calories when adults with obesity consumed strictly controlled diets. Results from the study are published in Cell Metabolism.

Non-diabetic men and women with obesity (n=19) at the NIH Clinical Center in Bethesda, MD stayed in the Metabolic Clinical Research Unit 24 hours per day for two extended visits. They ate the same food and performed the same activities. A baseline balanced diet was consumed for the first five days. Then for six days, subjects were given diets containing 30% fewer calories, which was achieved by reducing either total carbs or total fat from the baseline diet; the amount of protein stayed the same. Diets were switched during the second visit.

Restricting carbs decreased production of insulin and increased fat burning as expected; restricting fat had no changes in production of insulin or at fat burning. The reduced-carb diet was more effective at decreasing insulin secretion and increasing fat burn, leading to significant body fat loss. However, study subjects lost even more body fat during the reduced-fat diet from the greater imbalance between the fat consumed and fat burned.

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Study findings oppose the theory that body fat loss requires lowering insulin, thereby increasing the release of stored fat from fat tissue and the body burning more fat. Different types of calories impact metabolism and body composition, Griffin P. Rodgers, MD, director of NIDDK noted. For obese patients wanting to lose weight, it may be more important to consider which type of diet they will adhere to over time.

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