Long-term cafeteria feeding, cold exposure, and the combination of treatments increased energy intake in female Wistar rats by 25%, 113%, and 150%, respectively, in comparison with controls (P less than 0.01). Although cafeteria feeding at room temperature markedly increased the
insulin response to an intravenous
glucose tolerance test (IVGTT),
glucose tolerance was deteriorated (P less than 0.01). In contrast, cold exposure significantly improved
glucose tolerance in the presence of a reduced
insulin response in Purina- and cafeteria-fed animals. Moreover, cold exposure also decreased
body weight gain and increased brown adipose tissue mass, total
cytochrome-oxidase activity, and cellularity by approximately 600-800%. The results suggest that cold exposure enhances
insulin sensitivity of peripheral tissues, whereas
hyperphagia on a high-fat,
low-protein diet leads to
insulin resistance. In addition, the results demonstrate that prolonged stimulation of energy expenditure by cold exposure not only reverses the diabetogenic effects of cafeteria feeding but also improves
glucose tolerance. This phenomenon could result from a combination of two factors: (1) a cold-induced prevention of
obesity; and (2) an enhanced disposal of circulating
glucose into peripheral tissues, including brown adipose tissue.