Relationships between thermic effect of food, insulin resistance and autonomic nervous activity.

BACKGROUND The thermic effect of food (TEF) is higher in lean than in obese human subjects. OBJECTIVE Relationships between TEF and insulin resistance during meals, from the point of view of autonomic nervous activity, were evaluated. METHODS Autonomic nervous activity was evaluated in 20 young adults using the spectral analysis of heart rate variability from one hour before to two hours after a meal. Heart rate data were analyzed based on low frequency components (LF power, 0.04-0.15 Hz), high frequency components (HF power, 0.15-0.40 Hz), and LF/HF ratios. Energy expenditure and the TEF were measured 30 min after a meal. Homeostasis model of insulin resistance index (HOMA-IR) was also measured. RESULTS The LF/HF ratio was significantly increased 30 min after a meal (p<0.05). No correlation between LF power and HF power with TEF was found, but the LF/HF ratio was significantly and positively correlated with TEF (r=+0.56, p<0.05). Moreover, a significant negative correlation was found between the HOMA-IR and TEF (r=-0.601, p<0.05). CONCLUSIONS The findings suggest that a reduction in insulin sensitivity induces a poor response of sympathetic nervous activity in the postprandial phase and a reduction in postprandial energy expenditure.