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Long-term weight loss may be more likely with low-fat diet
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SAN DIEGO — Fat oxidation appears to increase quickly and plateau with a reduced carbohydrates diet compared with no change in fat oxidation when the same number of calories are cut from dietary fat, according to research presented here.
However, despite increased fat oxidation with the reduced carbohydrate diet, greater fat imbalance was observed during the low-fat eating regimen, leading to more body fat loss, according to researchers.
“Restriction of dietary carbohydrate led to an increase in whole body, 24-hour fat oxidation, whereas an isocaloric, or equal calorie, reduction of dietary fat in the same people had no significant effect on 24-hour fat oxidation,” Kevin D. Hall, PhD, of the NIH, said during a press conference. “The cumulative metabolic fat balance, adding up the daily imbalance between intake and expenditure of fat, indicated that the reduced-fat diet led to about 80% more body fat loss compared to the reduced carbohydrate diet.”
Kevin D. Hall
Hall and colleagues examined the effects of dietary carbohydrate vs. dietary fat restriction on whole-body energy expenditure and metabolic fat balance among 19 adults (10 men, 9 women; mean age, 34 ± 2 years) with obesity (mean BMI, 36 ± 1 kg/m2) but not diabetes.
Patients were admitted to a metabolic ward, fed a eucaloric baseline diet (2,720 ± 50 kcal/day; 50% carbohydrate, 35% fat, 15% protein) for 5 days, then to 6 days of a 30% reduced energy diet through restriction of either carbohydrate (LC) or dietary fat (LF).
The LC diet selectively removed 810 ± 30 kcal of carbohydrates per day, and patients were eating 30% carbohydrate, 49% fat and 21% protein. The LF diet selectively removed 811 ± 40 kcal of fat per day, and patients were consuming 72% carbohydrate, 7% fat and 21% protein.
After a washout period of 2 to 4 weeks, patients were readmitted to repeat the baseline diet, then crossed over to the alternate regimen. On days 2 and 5 of the baseline diet and days 1, 4 and 6 of the reduced energy diets, patients remained in a metabolic chamber. The researchers calculated body fat loss as cumulative metabolic fat imbalance during the restriction diet periods.
Similar decreases were observed for daily energy expenditure with LC and LF (130 ± 40 vs. 100 ± 30 kcal/day; P = .6), but patients had greater weight loss with LC compared with LF (1.9 ± 0.2 vs. 1.3 ± 0.1 kg; P = .01).
Whole-body fat oxidation rapidly increased and plateaued at 463 ± 60 kcal/day with LC (P < .0001) but showed no change with LF (38 ± 40 kcal/day; P = .37). However, patients had approximately 80% greater body fat loss after 6 days on the LF vs. LC regimen (443 ± 40 g vs. 245 ± 20 g; P < .0001).
“We did not address the long-term efficacy … the effect of prescribing … or the long-term health effects of a low-carbohydrate or low-fat diet,” Hall said.
Further research would need to look at how the diets compared in terms of continued body fat loss, ease or difficultly of following the diets, and health outcomes with adherence to the diets, he said. – by Allegra Tiver
Reference:
Hall KD, et al. Poster Board THR-553. Presented at: The Endocrine Society Annual Meeting; March 5-8, 2015, San Diego.
Disclosure: Hall reports no relevant financial disclosures.
Editor’s Note: On March 17, we corrected paragraphs seven, nine and 10 to clarify data. The Editors regret this error.