Yancy WS (Center for Health Services Research in Primary Care, Durham, NC)
Olsen MK (Center for Health Services Research in Primary Care, Durham, NC)
Westman EC (Duke University Medical Center)
A low-carbohydrate, ketogenic diet (LCKD) has demonstrated greater weight loss than a low-fat, energy-restricted diet (LFD) in several randomized, controlled trials but its effect on health-related quality of life (HRQOL) has not been reported. Our goal was to compare changes in HRQOL over 24 weeks in participants randomly assigned to follow one of these two diets.
We monitored HRQOL by participant self-report using the Medical Outcomes Study Short Form-36 (SF-36) in 119 overweight community volunteers who were randomized to a LCKD or a LFD and followed in an outpatient clinic. Mean scores, within-group changes from baseline to week 24, and between-group comparisons of these changes were calculated for the 8 separate subscales and the Physical Component and Mental Component Summary scores using linear mixed-effects models.
The mean age was 44.9 (SD=9.6) years; 76% were female; 76% were Caucasian; and the mean baseline BMI was 34.4 (SD=5.0) kg/m2. The mean weight loss was greater for the LCKD group (-12.9%) than the LFD group (-6.7%, p<0.001 for comparison). Significant improvements occurred in both diet groups for the Physical Function (LCKD: +7.1, p<0.001; LFD: +8.2, p<0.001), Role Physical (LCKD: +8.5, p=0.04; LFD: +9.1, p=0.04), General Health (LCKD: +5.8, p=0.004; LFD: +6.0, p=0.006), and Vitality subscales (LCKD: +14.1, p<0.001; LFD: +8.3, p=0.004), and the Physical Component Summary score (LCKD: +2.5, p=0.003; LFD: +4.1, p<0.001). Bodily Pain improved only in the LFD group (LCKD: +2.6, p=0.3; LFD: +6.3, p=0.03) whereas the Role Emotional (LCKD: +8.2, p=0.03; LFD: +3.9, p=0.3) and Mental Health (LCKD: +5.2, p=0.01; LFD: -1.1, p=0.6) subscales, and the Mental Component Summary (MCS) score (LCKD: +3.2, p=0.005; LFD: -0.4, p=0.8) improved in the LCKD group. In comparisons between groups, the LCKD group had greater improvement on the Mental Health subscale (p=0.04) and MCS score (p=0.04).
Mental health HRQOL improved to a greater degree in participants following a LCKD than in participants following a LFD. Given that obesity generally does not affect the mental aspects of HRQOL on the SF-36, the LCKD’s effect on this outcome deserves further research.
A low-carbohydrate diet favorably impacts mental health-related quality of life in addition to body weight.