Diet plays an important role in modulating exercise responses, including activation of the Growth Hormone (GH)/Insulin-like growth factor-I (IGF-1) axis. Obesity and fat ingestion were separately shown to reduce exercise GH responses, but their combined effect, especially important in children, has not been studied. We therefore measured the GH response to exercise (30-min intermittent cycling, ten 2-min bouts @ ~80% VO(2)max, separated by 1-min rest), started 45 min after ingestion of a high-fat meal (HFM) in 16 healthy (CTL, BMI% 51±7), and 19 obese (Ob, BMI% 97±0.4) children. Samples were drawn at baseline (pre-meal), and at start, peak and 30 min post exercise. In the Ob group a marked, ~ 75% suppression of the GH response (ng/mL) to exercise was observed (2.4±0.6 vs 10.6±2.1, p< 0.001). This levels of suppression was also significantly greater when compared to age-, fitness- and BMI- matched historical controls that had performed identical exercise in fasting conditions. Our data indicate that the reduction in the GH response to exercise, already present in obese children vs healthy controls, is considerably amplified by ingestion of fat nutrients shortly before exercise, implying a potentially downstream negative impact on growth factor homeostasis and long-term modulation of physiological growth.