Grant: Travel Awards - Institute Community Support

Alterations in fat oxidation (FatOx) are associated with insulin resistance in aging individuals and in first degree relatives (FDR) of diabetics. However, it remains unclear if a family history of diabetes influences FatOx in an aging, yet healthy, population. Our objective was to assess if FatOx is altered during submaximal aerobic exercise in aging FDR women compared with non-FDR women and to verify if circulating substrates influence FatOx. To verify our hypothesis, rates of FatOx, determined by respiratory exchange ratio (RER), were measured during 4 stages of submaximal exercise [1:40-45%, 2:50-55%, 3:60-65% and 4:70-75% of heart rate reserve] in 14 aging women (FDR: n=7; mean age: 61.9 ± 2.6 years; mean BMI: 28.2 ± 3.1 kg/m2). Blood samples were collected after each stage of exercise to measure plasma free fatty acids (FFA), glucose and lactate. We observed that RER and absolute rates of substrate oxidation were similar during exercise in FDR and non-FDR women. Likewise, plasma concentrations of substrates were similar at every stage of exercise between both groups. However, the crossover-point between FFA concentration and absolute rates of FatOx occurred at moderate intensity in non-FDR (stage 3) and at lower intensity in FDR (Stage 1). In conclusion, FDRs seem to display a disconnection between the capacity of oxidizing fat relative to FFA availability at a much lower aerobic workload which could be indicative of lower cardio-respiratory fitness.