Citations

▪ Abstract In vitro studies of adipocytes taken from different body fat regions suggest substantial differences in lipolysis between intra-abdominal, lower-body subcutaneous, and abdominal subcutaneous regions. Gender and obesity appear to influence these regional differences. In situ measurements of glycerol release from adipose tissue provided further evidence that regional heterogeneity of lipolysis occurs in humans. In vivo studies of regional free fatty acid (FFA) release have confirmed that adipose tissue lipolysis varies between upper- and lower-body fat. Release of FFA from lower-body adipose tissue is less than that from upper-body adipose tissue in both obese and non-obese men and women. In non-obese men and women, meal ingestion suppresses FFA release from all adipose tissue regions, and adrenergic stimulation activated FFA release from different sites in a gender-specific fashion. Significant regional and gender differences in adipose tissue lipolysis occur in humans, and this could contribute to differences in the health effects of adipose tissue and could theoretically influence body fat distribution.

Humans show considerable interindividual variation in susceptibility to weight gain in response to overeating. The physiological basis of this variation was investigated by measuring changes in energy storage and expenditure in 16 nonobese volunteers who were fed 1000 kilocalories per day in excess of weight-maintenance requirements for 8 weeks. Two-thirds of the increases in total daily energy expenditure was due to increased nonexercise activity thermogenesis (NEAT), which is associated with fidgeting, maintenance of posture, and other physical activities of daily life. Changes in NEAT accounted for the 10-fold differences in fat storage that occurred and directly predicted resistance to fat gain with overfeeding (correlation coefficient = 0.77, probability < 0.001). These results suggest that as humans overeat, activation of NEAT dissipates excess energy to preserve leanness and that failure to activate NEAT may result in ready fat gain.