The test was to walk for 60 minutes on a treadmill. Not eating before walking affected blood biomarkers, but it was changes to the responses of the fat cells and gene expression that were the most interesting.
To find out, they first recruited 10 overweight and sedentary but otherwise healthy young men, whose lifestyles are, for better and worse, representative of those of most of us. (They did not recruit women because it is difficult to control for the effects of the menstrual cycle on metabolism; they hope to study women in the future.)
Not everybody can exercise comfortably on an empty stomach, and if it’s not comfortable for you don’t do it. My motto is that if I’m not hungry, I don’t eat, so there are days when I walk on the treadmill fasted. But if I’m hungry before walking, I eat.
Before one of these workouts, the men skipped breakfast, meaning that they exercised on a completely empty stomach, after a prolonged overnight fast.
On the other occasion, they ate a substantial, 600-calorie morning meal, supplied by the scientists, of toast, jam, cereal, milk and orange juice about two hours before they started walking.
Feeding profoundly affects metabolic responses to exercise in various tissues but the effect of feeding status on human adipose tissue responses to exercise has never been studied. Ten healthy overweight men aged 26 ± 5 years (mean ± SD) with a waist circumference of 105 ± 10 cm walked at 60% of maximum oxygen uptake under either FASTED or FED conditions in a randomised, counterbalanced design. Feeding comprised 648 ± 115 kcal 2 h before exercise. Blood samples were collected at regular intervals to examine changes in metabolic parameters and adipokine concentrations. Adipose tissue samples were obtained at baseline and one hour post-exercise to examine changes in adipose tissue mRNA expression and secretion of selected adipokines ex-vivo. Adipose tissue mRNA expression of PDK4, ATGL, 29 HSL, FAT/CD36, GLUT4 and IRS2 in response to exercise were lower in FED compared to FASTED conditions (all p ≤ 0.05). Post-exercise adipose IRS2 protein was affected by feeding (p ≤ 0.05), but Akt2, AMPK, IRS1, GLUT4, PDK4 and HSL protein levels were not different. Feeding status did not impact serum and ex-vivo adipose secretion of IL-6, leptin or adiponectin in response to exercise. This is the first study to show that feeding prior to acute exercise affects post-exercise adipose tissue gene expression and we propose that feeding is likely to blunt long-term adipose tissue adaptation to regular exercise.