Abstract P263: Acid-Base Status as a Modifier of Loss of Lean Mass During Intentional Weight Loss in Older Adults

Weight loss interventions present a unique challenge in older adults: relative loss of lean mass during weight loss, if superimposed on age-related sarcopenia may increase the risk for mobility disability. Relative loss of lean mass (25-30%) during weight loss depends on the severity/duration of caloric restriction, initial body mass, and concomitant exercise training. We hypothesized that subclinical imbalances of acid-base status (reflected in lower serum bicarbonate) may also affect relative loss of lean mass during weight loss. The rationale: even subtle imbalances of acid-base status (e.g. bicarbonate <23 mmol) impact clinical outcomes in older adults such as gait speed or incidence of functional limitation, while bicarbonate supplementation reduces urinary nitrogen wasting and may improve physical function. However, data on acid-base balance and serum bicarbonate during moderate caloric restriction are lacking. We, therefore, analyzed 2 randomized, controlled weight loss trials (including moderate caloric restriction and exercise): The Diet, Exercise, and Metabolism for Older Women [DEMO; (58±5.2 y)] and Cooperative Lifestyle Program; [CLIP; (67±4.7 y)]. Serum bicarbonate was assessed as total CO 2 (in mmol) and whole body lean mass measured by dual-energy X-ray absorptiometry. The analysis showed that 48% of participants had bicarbonate <23. DEMO participants with lower serum bicarbonate at baseline lost more lean mass during the intervention (unadjusted β(SE)=0.32(0.16); p=0.04; n=92). Adjustments for age, BMI, eGFR, % weight loss, baseline, intervention group, had little effect, but adjusting for protein intake during weight loss attenuated the association (β(SE)=0.17(0.15); p=0.28.). Similarly, a change in serum bicarbonate during the trial was associated with % lean mass change, but attenuated after controlling for protein intake. This is not unexpected: protein is acid-producing and one of two major determinants of net dietary acid load; higher dietary acid load correlates with lower serum bicarbonate, in older adults. Results from the CLIP trial were remarkably similar, and consistently, baseline serum bicarbonate level was marginally predictive of baseline daily protein intake, with highest baseline serum bicarbonate having the lowest protein intake [bicarbonate: >24 (n=58); >21-24 (n=121); <21 (N=93); protein in g/kg body weight 0.7(0.4); 0.9(0.4); 0.8(0.4) respectively, p=0.057). In conclusion, our analysis suggests that higher serum bicarbonate before and during weight loss may ameliorate loss of lean mass, however, to obtain definitive answer such analysis needs to be conducted under conditions of controlled or randomized protein intake. Importantly, our findings suggest that oral bicarbonate supplementation, a simple and relatively safe intervention, may ameliorate loss of lean mass during weight loss interventions in older adults.