RESPONSE OF SERUM LEPTIN CONCENTRATIONS TO 7 D OF ENERGY RESTRICTION IN CENTRALLY OBESE AFRICAN-AMERICANS WITH IMPAIRED OR DIABETIC GLUCOSE-TOLERANCE

The aim of this study was to determine whether serum leptin concentrat ions are reduced in response to short-term energy restriction in centr ally obese individuals with impaired glucose tolerance or non-insulin- dependent diabetes mellitus. Twenty African Americans [16 females and 4 males, 44 +/- 7 y ((x) over bar +/- SD), 107.2 +/- 23.8 kg, 39 +/- 7 % body fat] consumed a 7-d energy-restricted diet (4.03 +/- 0.72 MJ/d) of whole foods. Oral-glucose-tolerance tests (OGTTs) were performed b efore and immediately after the diet to assess changes in serum leptin , glucose, and insulin concentrations. Baseline leptin concentration c orrelated significantly with percentage body fat (r = 0.80), body mass index (r = 0.72), fat mass (r = 0.64), waist-height ratio (r = 0.61), body weight (r = 0.59, all P < 0.01), waist circumference (r = 0.49), and basal insulin concentration (r = 0.48, both P < 0.05). Seven days of energy restriction resulted in significant reductions (P < 0.005) in leptin (-6.1 +/- 8.4 mu g/L), basal glucose (-0.9 +/- 0.8 mmol/L), OGTT glucose area under the curve (-158 +/- 164 mmol/L), and basal ins ulin concentration (-34 +/- 69 pmol/L, P < 0.05). In addition, there w as a trend for a reduction in OGTT insulin area under the curve (-15 5 67 +/- 33 658 pmol/L, P = 0.05), and a tendency for basal insulin and leptin to change together (r = 0.41, P = 0.07). Despite the weight los s of 3.1 +/- 1.3 kg (P < 0.0001), the loss of fat mass was calculated to be only -1.0 +/- 0.1 kg. These results suggest that negative energy balance or improved insulin action was responsible for the changes in leptin, glucose, and insulin concentrations. In summary, short-term e nergy restriction effectively reduced serum leptin concentrations and improved glucose tolerance and insulin action in obese individuals wit h impaired or diabetic glucose tolerance.