(HealthDay News) – Both aerobic and resistance exercise (without calorie restriction) reduce fat and improve fitness in obese adolescent boys, although only resistance exercise improves insulin sensitivity, according to a study published online June 29 in Diabetes.

SoJung Lee, PhD, from the University of Pittsburgh, and colleagues randomly assigned 45 obese adolescent boys (12 to 18 years old; without diabetes; physically inactive) to a 3-month program (180 minutes per week) of aerobic exercise, resistance exercise, or no exercise (all without caloric restriction).

The researchers found that the no-exercise group had significant weight gain but that this was prevented with aerobic and resistance exercise. Both exercise groups had significant reductions in total fat, visceral fat, waist circumference, and intrahepatic lipid, as well as improvement in cardiorespiratory fitness. However, only the resistance-exercise group had a significant improvement in insulin sensitivity (27%), skeletal muscle mass, and muscular strength. Overall, changes in visceral fat were associated with changes in intrahepatic lipid and insulin sensitivity.

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“In summary, both aerobic and resistance exercise without caloric restriction are effective for reducing abdominal fat and intrahepatic lipid in moderately obese adolescent boys,” Lee and colleagues conclude. “Resistance exercise but not aerobic exercise is also associated with significant improvements in insulin sensitivity.”

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