Should you eat before working out?

Published 5.1.2017
At least for men, the answer might be to not eat before working out. Women were not included in the trial because… hormones. Where a woman is in her menstrual cycle makes a huge difference in her hormonal biomarkers, making analysis much more difficult. The default answer to this inconvenient fact is to punt, and jut not include women in the trial. Or to use post-menopausal women, which is useful, but not for younger women.

It's almost as though females weren't half the population, or that the technology to track a females hormonal cycle didn't exist. Yes, making sure that female subjects exercise in the same phase of their cycle adds a level of logistical difficulty. Or recruit subjects all in the same phase, which would probably mean additional interviews and testing. Bottom line: it can and should be done.

In any event, researchers tried to answer the question for young, healthy, overweight and obese male subjects.

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.)

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.

Changes in the fat cells were measured by taking biopsies of subcutaneous fat cells from the volunteers. The genes that were altered can affect blood glucose and insulin levels. Fasting before walking made these genes more active.

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.

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.

The study doesn’t say what happens if there is a shorter fast before exercising, say, eating lunch, but then exercising 6 hours later before dinner. Frankly, I’m not convinced that the difference is enough to worry about. If this is something that you can do without stress, then do it.

This is the link to the study and its abstract:

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.

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