1. In this randomized controlled trial, calorie restriction (CR) by 25% in non-obese healthy adults resulted in improved quality of life, mood, sexual function and sleep compared to an ad-libitum (AL) control group.
2. While the quality of life was improved in this study for non-obese individuals, the means to effectively cut calories remains unexplored and thus may not be easily translated in daily practice.
Evidence Rating Level: 1 (Excellent)
Study Rundown: The CALERIE-2 randomized trial showed improvements of chronic disease risk factors with calorie restriction (CR) even in non-obese individuals. However, psychological and endocrine outcomes were not studied, and there was concern that CR may result in potential negative effects in these domains. This randomized trial tested the effect of 2-year 25% CR on mood, quality of life (QOL), sleep, and sexual function in healthy non-obese adults.
The CR group lost significantly more weight, had significantly improved mood, reduced tension, improved general health, and sexual drive and relationships as determined by participant self-reported outcomes at 24 months. CR participants also reported significantly improved sleep at 12 months as compared to the AL group. Strengths of this study included use of multiple validated self-report questionnaires for the QOL measures. However, inability to blind the study group and reliance on self-reported data limit the reliability of the results.
In-Depth [randomized controlled trial]: This parallel-group randomized controlled trial was conducted across 3 academic research institutions in the USA from January 2007 to March 2012. Adult men and women with body mass indexes (BMI) from 22.0 to 28.0 were included in the study and randomized to 2 years of 25% reduction in caloric intake or an ad libitum (AL) control group at a ratio of 2:1, CR to AL. Baseline sociodemographic and clinical information was gathered. Outcomes of interest include multiple self-report questionnaires to measure mood (Beck Depression Inventory-II [BDI-II], Profile of Mood States [POMS]), QOL (Rand-36 Short form, Perceived Stress Scale), sleep (Pittsburgh Sleep Quality Index [PSQI]), and sexual function (Derogatis Interview for Sexual Function-self-report). These outcomes were gathered at baseline, at 12 and 24 months. Intention-to-treat statistical analysis was used alongside a mixed-models repeated-measures analysis.
Of a total of 238 eligible individuals, 220 men and women were randomized to 25% CR (n = 145) or AL (n = 75). The CR group lost significantly more weight than the AL group (7.6kg (0.3 SE) vs. 0.4kg (0.5 SE), respectively, at month 24 (p < 0.001). Compared to the AL group, participants randomized to CR experienced better mood (BDI-II between group difference [BGD] -0.76, 95%CI -1.41 to -0.11), reduced tension (POMS: BGD -0.79, 95%CI -1.38 to -0.19), improved general health (BGD 6.45, 95%CI 3.93 to 8.98) and sexual drive (BGD 1.06; 95%CI 0.11-2.01) at month 24 of follow-up. They also had improved sleep duration at month 12 (BGD: -0.26, 95%CI -0.49 to -0.02). All of these differences were statistically significant.
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