We determined if interval exercise plus a low-calorie diet (LCD+INT) increases endothelial function more than an energy-matched LCD. Obese women (47.2 +/- 2.6 y, 37.5 +/- 1.3 kg/m2) were randomized to 13 days of a LCD (n = 12; mixed meals of approximately 1,200 kcal/d) or LCD+INT (n = 13; 12 supervised 60-min INT bouts of 3 min at 90% and 50% HRpeak). LCD+INT subjects received 350 kcal postexercise to equate energy availability with LCD. Fitness (VO2peak) and body composition (BodPod) were determined and a 120 min, 75 g oral glucose tolerance test was performed to examine fasting and postprandial flow-mediated dilation (FMD, endothelial function), respiratory exchange ratio (RER) via indirect calorimetry as well as glucose and insulin incremental area under the curve (iAUC120min). LCD+INT increased VO2peak (p = 0.02) compared with LCD, and both treatments decreased fat mass (p < 0.001) and insulin iAUC120min (p = 0.03). There was no overall treatment effect on fasting or iAUC120min FMD. However, in participants who increased fasting endothelial function after each treatment (delta > 50%; LCD n = 5, LCD+INT n = 7), LCD+INT increased fasted (p = 0.005) and decreased iAUC120min (p = 0.003) FMD compared with LCD. Enhanced fitness correlated with increased fasting FMD (r = 0.43, p = 0.03) and diminished FMD iAUC120min (r = -0.44, p = 0.03). Decreased FMD iAUC120min correlated with reduced glucose iAUC120min (r = 0.64, p = 0.001) as well as increased 60-min RER (r = -0.42, p = 0.04). Low baseline fasting and iAUC120min FMD was also linked to enhanced fasting and iAUC120min FMD post-treatment (r = -0.71, p < 0.001; r = -0.89, p < 0.001, respectively). In conclusion, increasing fitness via INT may increase the effect of LCD on lowering cardiovascular disease risk in obese women.

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