It’s a new year, which means hordes of new (or returning) gym-goers will hit the benches and ellipticals. Thanks to great marketing, more than of few of us have heard of the PWS (pre-workout snack), either a shake or protein bar or whatever else fitness nutrition companies are trying to sell. But should you eat before working out and exercising?
Researchers at the University of Saskatchewan in Saskatoon, Canada published in the International Journal of Sport Nutrition and Exercise Metabolism their findings on how what you eat (or don’t eat) before exercise can impact performance. In a single-blinded study of 16 male participants, Little et al. had participants perform 90 minutes of high-intensity running trials after each eating either an isonenergetic and low glycemic-index food (lentils), a high glycemic index food (potatoes and egg whites), or no food at all. The study participants repeated with each pre-workout treatment after 7 days of completing the previous to recover.
Each participant reported to the laboratory 6 h post-prandial and after sitting for 5 min, a basal venous blood sample and a 5 min resting expired air sample was collected via standard open circuit spirometry. They were then provided with a [sic] standardised meal that provided 1 g kg BM−1 of carbohydrate and was composed of either high or low GI carbohydrates. The participants consumed the meal within 10 min, then rested for 45 min before they commenced the exercise protocol. A 15 min post-prandial venous blood sample was then collected and a heart rate (HR) monitor was attached to the participant. A final pre-exercise venous blood sample was obtained 10 min before the onset of exercise.
Results are fairly expected: when subjects ate anything before exercise, they had higher fatty acids in blood serum and lower insulin. Participants ran further after eating both low-GI and high-GI food, but they reported less exertion only after eating low-GI foods.
- The low GI meal appears to be associated with greater availability of carbohydrate throughout the exercise period, which may have sustained energy production towards the end of exercise.
- Therefore, consuming a low GI carbohydrate meal providing 1 g kg−1 body mass of carbohydrate, 45 min prior to endurance performance may have a beneficial effect on time trial performance.
Researchers postulate that eating before exercise increases availability of glycogen (glucose polymer that stores energy) to muscles.