The Study

The resting metabolic rate (RMR) decrease, observed after an obesity reduction therapy is a determinant of a short-time weight regain. Thus, the objective of this study was to evaluate changes in RMR, and the associated hormonal alterations in obese patients with a very low-calorie ketogenic (VLCK)-diet induced severe body weight (BW) loss.

Methods

From 20 obese patients who lost 20.2 kg of BW after a 4-months VLCK-diet, blood samples and body composition analysis, determined by DXA and MF-Bioimpedance, and RMR by indirect calorimetry, were obtained on four subsequent visits: visit C-1, basal, initial fat mass (FM) and free fat mass (FFM); visit C-2, − 7.2 kg in FM, − 4. 3 kg in FFM, maximal ketosis; visit C-3, − 14.4 kg FM, − 4.5 kg FFM, low ketosis; visit C-4, − 16.5 kg FM, − 3.8 kg FFM, no ketosis. Each subject acted as his own control.

Results

Despite the large body weight reduction, measured RMR varied from basal visit C-1 to visit C-2, − 1.0%; visit C-3, − 2.4% and visit C-4, − 8.0%, without statistical significance. No metabolic adaptation was observed. The absent reduction in RMR was not due to increased sympathetic tone, as thyroid hormones, catecholamines, and leptin were reduced at any visit from baseline. Under regression analysis FFM, adjusted by levels of ketonic bodies, was the only predictor of the RMR changes (R2 = 0.36; p < 0.001).

Conclusion

The rapid and sustained weight and fat mass loss induced by a very low-calorie ketogenic diet in obese subjects did not induce the expected reduction in resting metabolic rate, probably due to the preservation of lean mass. So, this study shows a very low-calorie ketogenic diet favors the maintenance and avoids the metabolic adaptation phenomenon. This finding might explain the long-term positive effects of very low-calorie ketogenic diet on weight loss.

Although, the mechanisms by which this effect could be justified are unclear, classical determinants of the energy expenditure, as thyroid hormones, catecholamines as well as leptin were discarded. The relative good preservation of FFM (muscle mass) observed with this dietetic approach could be the cause for the absence of metabolic adaptation.

Citation

Gomez-Arbelaez D, Crujeiras AB, Castro AI, Martinez-Olmos MA, Canton A, Ordoñez-Mayan L, Sajoux I, Galban C, Bellido D, Casanueva FF. Resting metabolic rate of obese patients under very low calorie ketogenic diet. Nutr Metab (Lond). 2018;15:18.