Carbs at night does not increase performance

Endurance athletes who eat extra carbs at night, just before going to sleep, won’t perform better the next day. But they will burn a little less fat and a few more carbs, wrote American sports scientist Michael Ormsbee, of Florida State University, in Applied Physiology, Nutrition and Metabolism.

The researchers got 12 trained female runners and triathletes to run 10 kilometres on a treadmill on different occasions.

On the evening before doing the trial, before they went to bed, the women drank on one occasion a placebo containing no nutrients. On another occasion they drank 335 millilitres of skimmed chocolate milk – which was good for 180 kilocalories, 30 g carbs and 12 g protein.

The researchers used TruMoo Chocolate Milk.

In terms of their times, it made no difference whether the athletes had drunk chocolate milk or a placebo.

Yet the chocolate milk did change the athletes’ metabolism. When the researchers got the participants to run at moderate intensity on a treadmill for 15 minutes before they did the 10-K trial, the athletes burned a little more carbohydrate and a little less fat if they had drunk chocolate milk the night before.

The chocolate milk may have had an adverse effect on the participants’ sleep. After drinking the placebo, one 1 athlete reported abnormal sleep. After drinking the chocolate milk, 4 reported abnormal sleep. In addition, the chocolate milk increased the participants’ appetite the next day.

“In summary, pre-sleep chocolate milk seems to alter next-morning resting and exercise metabolism in female athletes,” the researchers summarised. “Specifically, nighttime chocolate milk increases […] carbohydrate oxidation at a range of submaximal intensities.”

“This is the first research to show effects to exercise metabolism greater than 4 hours after meal ingestion.”

“While the potential effects observed to metabolism are novel, they did not translate to improved 10-km running performance.”

Nighttime feeding likely alters morning metabolism but not exercise performance in female athletes


The timing of morning endurance competition may limit proper pre-race fueling and resulting performance. A nighttime, pre-sleep nutritional strategy could be an alternative method to target the metabolic and hydrating needs of the early morning athlete without compromising sleep or gastrointestinal comfort during exercise. Therefore, the purpose of this investigation was to examine the acute effects of pre-sleep chocolate milk (CM) ingestion on next-morning running performance, metabolism, and hydration status. Twelve competitive female runners and triathletes (age, 30 ± 7 years; peak oxygen consumption, 53 ± 4 mL·kg−1·min−1) randomly ingested either pre-sleep CM or non-nutritive placebo (PL) ∼30 min before sleep and 7–9 h before a morning exercise trial. Resting metabolic rate (RMR) was assessed prior to exercise. The exercise trial included a warm-up, three 5-min incremental workloads at 55%, 65%, and 75% peak oxygen consumption, and a 10-km treadmill time trial (TT). Physiological responses were assessed prior, during (incremental and TT), and postexercise. Paired t tests and magnitude-based inferences were used to determine treatment differences. TT performances were not different (“most likely trivial” improvement with CM) between conditions (PL: 52.8 ± 8.4 min vs CM: 52.8 ± 8.0 min). RMR was “likely” increased (4.8%) and total carbohydrate oxidation (g·min−1) during exercise was “possibly” or likely increased (18.8%, 10.1%, 9.1% for stage 1–3, respectively) with CM versus PL. There were no consistent changes to hydration indices. In conclusion, pre-sleep CM may alter next-morning resting and exercise metabolism to favor carbohydrate oxidation, but effects did not translate to 10-km running performance improvements.