Is a Calorie a Calorie? Metabolic Fat Balance Following Selective Isocaloric Restriction of Dietary Carbohydrate Vs. Fat in Obese Adults

Program: Abstracts - Orals, Poster Previews, and Posters
Session: THR 549-580-Obesity: Clinical Studies
Thursday, March 5, 2015: 1:00 PM-3:00 PM
Hall D-F, Obesity (San Diego Convention Center)

Poster Board THR-553
Kevin D Hall, Ph.D.1, Thomas Bemis1, Robert J Brychta, Ph.D1, Kong Chen, Ph.D1, Amber B Courville, Ph.D2, Stephanie Goodwin, Ph.D.1, Juen Guo, Ph.D.1, Lilian Howard, N.P.1, Nicolas D Knuth, Ph.D.3, Bernard V Miller III, M.D.1, Carla M Prado, Ph.D.4, Emma Preuschl1, Mario Siervo, M.D., Ph.D.5, Monica C. Skarulis, M.D.1 and Laura Yannai1
1NIH, Bethesda, MD, 2Clinical Center, NIH, Bethesda, MD, 3Towson University, Towson, MD, 4University of Alberta, Edmonton, AB, Canada, 5MRC Human Nutrition, Cambridge, United Kingdom
Dietary carbohydrate restriction has been hypothesized to induce metabolic and endocrine changes that promote increased adipose tissue lipolysis and fat oxidation thereby leading to greater body fat loss than isocaloric dietary fat restriction. While clinical weight loss trials have typically found that low carbohydrate diets cause greater short-term weight loss, diet adherence during outpatient interventions is uncertain and all three macronutrients were likely to have been altered. Therefore, the selective effect of restricting carbohydrate vs. fat on energy and macronutrient balance has yet to be determined.

We investigated whole-body energy expenditure and metabolic fat balance resulting from selective restriction of dietary carbohydrate vs. dietary fat in 19 obese, non-diabetic adults (10M/9F) with mean (±SE) age of 34±2 y and BMI of 36±1 kg/m2. Subjects were admitted to a metabolic ward and fed a eucaloric baseline diet (50% carbohydrate, 35 % fat, 15% protein) for 5 days followed by random assignment to 6 days of a 30% reduced energy diet achieved solely by restriction of either dietary fat (LF) or carbohydrate (LC). Volunteers were crossed-over and readmitted after a 2-4 week washout to repeat the baseline diet and alternate LC or LF diet. Subjects resided in a metabolic chamber on days 2 and 5 of the baseline diet and days 1, 4, and 6 of the reduced energy diets. Body fat loss was calculated as the cumulative metabolic fat imbalance during each LC and LF diet period.

After 5 inpatient days consuming 2720±50 kcal/d of the eucaloric baseline diet, the LC diet selectively removed 790 ± 20 kcal/d of carbohydrate such that the subjects were eating 30% carbohydrate, 49% fat, and 21% protein. The alternate LF diet selectively removed 800 ± 20 kcal/d of fat from the baseline diet such that the subjects were consuming 72% carbohydrate, 7% fat, and 21% protein. Daily energy expenditure decreased similarly on LC and LF diets (72±30 vs. 81±20 kcal/d; p=0.76) but more weight was lost with LC vs. LF (1.9±0.2 vs. 1.3±0.1 kg; p=0.05). Whole-body fat oxidation rapidly increased during the LC diet and reached a plateau at 426±40 kcal/d (p<0.0001) but was unchanged on the LF diet (-53±40 kcal/d; p=0.15). However, body fat loss was ~67% greater after 6 days of LF vs. LC (394±40 vs. 236±30 g; p=0.0003).

Long-term extrapolation of our results is fraught with difficulties. However, our data demonstrated that the LC diet increased fat oxidation rapidly and plateaued at ~400 kcal/d above fat intake. In contrast, the isocaloric LF diet demonstrated no change in fat oxidation despite reducing fat intake by ~800 kcal/d, thereby leading to a greater degree of fat imbalance. While fat oxidation during prolonged LF and LC diets would be expected to slowly wane over time, our data suggest that the greater fat imbalance is likely to persist with the LF diet leading to more long-term body fat loss than with the LC diet.

Nothing to Disclose: KDH, TB, RJB, KC, ABC, SG, JG, LH, NDK, BVM III, CMP, EP, MS, MCS, LY

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Sources of Research Support: NIDDK Intramural 1ZIADK013037-07