Impact of Protein Intake during Weight Loss on Preservation of Fat-Free Mass, Resting Energy Expenditure, and Physical Function in Overweight Postmenopausal Women: A Randomized Controlled Trial

Abstract

<b><i>Introduction:</i></b> Weight loss in old age increases the risk of sarcopenia caused by the age-related reduction of fat-free mass (FFM). Due to the strong correlation between FFM and resting energy expenditure (REE), the maintenance of this must also be considered. Besides, the physical function (PF) must be maintained. <b><i>Objective:</i></b> The impact of protein intake on changes in FFM, REE, and PF during weight loss in overweight postmenopausal women was investigated. <b><i>Methods:</i></b> Fifty-four postmenopausal women (BMI 30.9 ± 3.4; age 59 ± 7 years) were randomized into 2 groups receiving energy-restricted diets with either 0.8 g (normal protein; NP) or 1.5 g protein/kg body weight (high protein; HP) for 12 weeks, followed by a 6-month follow-up phase with an ad libitum food intake. FFM, REE, and PF (strength, endurance, and balance) were measured at baseline, after weight loss, and after follow-up. <b><i>Results:</i></b> Forty-six women completed the weight loss intervention and 29 were followed up. The weight loss was –4.6 ± 3.6 kg (HP) and –5.2 ± 3.4 kg (NP; both <i>p</i> &#x3c; 0.001) and the weight regain during follow-up was 1.3 ± 2.8 kg (HP; <i>p</i> = 0.03) and 0.4 ± 2.5 kg (NP; <i>p</i> = 0.39), with no differences between groups. Similar decreases in FFM (–0.9 ± 1.1 [HP] vs. –1.0 ± 1.3 kg [NP]) and REE (–862 ± 569 [HP] vs. –1,000 ± 561 kJ [NP]; both <i>p</i> &#x3c; 0.001) were observed in both groups. During follow-up, no changes in FFM were detected in either group, whereas in the NP group the REE increased again (+138 ± 296; <i>p</i> = 0.02). The main determinants of FFM loss were the energy deficit and the speed of weight loss. In the NP group, the Short Physical Performance Battery score improved with weight loss (+0.6 ± 0.8; <i>p</i> &#x3c; 0.001) and handgrip strength decreased (–1.7 ± 3.4 kg; <i>p</i> &#x3c; 0.001), whereas no changes were observed in the HP group. <b><i>Conclusions:</i></b> An HP weight-loss diet without exercise had no impact on preservation of FFM and REE but may help to maintain muscle strength in postmenopausal women.