Energy expenditure and body composition changes after an isocaloric ketogenic diet in overweight and obese men: A secondary analysis of energy expenditure and physical activity

Abstract

Background

A previously published pilot study assessed energy expenditure (EE) of participants with overweight and obesity after they were switched from a baseline high-carbohydrate diet (BD) to an isocaloric low-carbohydrate ketogenic diet (KD). EE measured using metabolic chambers increased transiently by what was considered a relatively small extent after the switch to the KD, whereas EE measured using doubly labeled water (EE _DLW) increased to a greater degree after the response in the chambers had waned. Using a publicly available dataset, we examined the effect of housing conditions on the magnitude of the increase in EE _DLW after the switch to the KD and the role of physical activity in that response.

Methods

The 14-day EE _DLW measurement period included 4 days when subjects were confined to chambers instead of living in wards. To determine the effect on EE _DLW only for the days subjects were living in the wards, we calculated non-chamber EE (EE _nonchamber). To assess the role of physical activity in the response to the KD, we analyzed chamber and non-chamber accelerometer data for the BD and KD EE _DLW measurement periods.

Results

In comparison with the increase in average 14-day EE _DLW of 151 kcal/d ± 63 ( P = 0.03) after the switch to the KD, EE _nonchamber increased by 203 ± 89 kcal/d ( P = 0.04) or 283 ± 116 kcal/d ( P = 0.03) depending on the analytical approach. Hip accelerometer counts decreased significantly ( P = 0.01) after the switch to the KD, whereas wrist and ankle accelerometer counts did not change.

Conclusions

Switching from the BD to the KD substantially increased EE _DLW, but apparently only on days subjects were living in the ward outside the metabolic chamber. Increased physical activity as measured by accelerometry did not appear to account for this effect.