The main finding of the summarized study was that consuming two meals (breakfast and lunch) before exercise did not improve resistance exercise performance compared to consuming one meal (lunch). Does this finding agree with the results of other similar studies?

There are three main studies within this area of research to consider. In the first study, published in 2015, young, recreationally active men who habitually consumed breakfast consumed either a standardized breakfast or no breakfast followed by an ad libitum lunch meal before completing a 30-minute work capacity test on a cycle ergometer.^[1] The researchers observed that when the participants consumed breakfast, they performed more total work during the cycling test.

In the second study, published in 2019, 10 competitive collegiate rowers (8 women and 2 men) who habitually ate breakfast consumed either a standardized breakfast before 9 a.m. or extended their overnight fast until 12 p.m. After 12 p.m., the participants consumed food and beverages ad libitum before completing a 2,000-meter time trial on a rowing ergometer between 4:30 p.m. and 6 p.m.^[2] The researchers found that when the participants consumed breakfast, it took them less time to complete the time trial.

In the third study, published in 2021, young, highly-trained cyclists who habitually consumed breakfast consumed either a standardized breakfast or no breakfast followed by a standardized lunch before completing a 20-kilometer time trial on a cycle ergometer.^[3] The researchers found that when the participants consumed breakfast, it took them less time to complete the time trial.

A major difference between the first two studies and the third study is that overall energy and macronutrient intakes were not equated between conditions in the first two. In the first two studies, when the participants skipped breakfast, their overall energy intake prior to exercise was about 350–540 kcal lower than when they consumed breakfast. This difference in energy and carbohydrate intake was apparently sufficient to impair exercise performance to a statistically significant degree in the breakfast-skipping condition.

The third study reported that, despite equal energy and carbohydrate intake between conditions, performance was worse when breakfast was skipped. This finding is in contrast to that of the summarized study, which also equated energy and carbohydrate intake between conditions. What might explain this disagreement between the results of the third study and the summarized study?

One explanation is the type of exercise the participants performed (i.e., endurance vs. resistance exercise). The evidence supporting the benefits of carbohydrate availability on exercise performance is much more robust and consistent for endurance exercise compared to resistance exercise.^[4] Higher preexercise skeletal muscle and liver glycogen levels can enhance endurance exercise performance.^[5] However, the relationship between preexercise glycogen levels and performance during shorter-duration high-intensity exercise is more ambiguous.^[6]

It’s hypothesized that consuming one meal before exercise, compared to two meals, results in less glycogen storage, which leads to inferior performance.^[3] In support of this idea, previous evidence suggests that consuming breakfast leads to greater increases in muscle glycogen storage after lunch compared to skipping breakfast.^[7] So the effect of consuming two meals before exercise, compared to one, may be stronger in the context of endurance exercise performance than resistance exercise performance because endurance exercise is more likely to benefit from higher carbohydrate availability. That said, breakfast consumption in the third study boosted performance by about 3.4%, the practical significance of which is ultimately dependent upon the caliber of the athlete and their goals.

A second idea is related to the timing of the preexercise meal. The third study had the participants consume lunch (the preexercise meal) 4–5 hours before the exercise test, whereas the summarized study had the participants consume lunch 1.5–3 hours before the exercise test. Current sports nutrition guidelines recommend consuming carbohydrates within 1–4 hours of exercise.^[8] As such, it might be the case that when the timing of the preexercise meal falls outside of this window, the effect of prior meal consumption is more notable.

Another possibility has to do with the population studied. The third study included only habitual breakfast consumers, whereas the summarized study included both habitual and nonhabitual breakfast consumers. Previous evidence indicates that habitual breakfast consumers derive a psychological benefit from perceived breakfast consumption that positively affects exercise performance. In one study examining performance during a 20-minute cycling time trial and another examining performance during multiple sets of back squats, the researchers reported that consuming a carbohydrate-rich breakfast did not improve exercise performance compared to a taste-matched and texture-matched low-energy placebo breakfast.^[9]^[10]

Therefore, because all of the participants in the third study were habitual breakfast consumers, their beliefs about the effect of breakfast consumption on exercise performance may have influenced the results. If the participants expected breakfast consumption to improve their exercise performance, and consequently, it did, they experienced the placebo effect. Alternatively, if the participants expected skipping breakfast to impair their exercise performance, and consequently, it did, they experienced the nocebo effect.

In comparison, because the summarized study included both habitual and nonhabitual breakfast consumers, it’s possible that a placebo/nocebo effect was realized in habitual breakfast consumers, but not nonhabitual breakfast consumers, and so when the data from all of the participants were aggregated, there was no overall effect of breakfast consumption. However, in contrast to this theory, whether the participant habitually consumed breakfast was not reported to influence exercise performance: habitual breakfast consumers performed similarly between conditions.

Placebo and nocebo effects on exercise performance

Ultimately, whether consuming two meals before exercise is superior to one for exercise performance is unclear. Further research is needed to determine whether consuming the same amount of energy split between two meals (breakfast and lunch) or within a single meal (lunch) results in differences in late afternoon/evening exercise performance, and whether the type of exercise (i.e., endurance vs. resistance exercise) or the timing of the preexercise meal influences the effect.

Are two preworkout meals better than one? Original paper