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Researchers at the University of Toronto have found that in healthy females, a post-meal rise in blood sugar was lower if they waited until after breakfast to exercise.

The researchers in the Faculty of Kinesiology & Physical Education (KPE) also measured perceptions of appetite before and after exercise – and once every hour in the post-exercise period.

They found that study participants who exercised after eating breakfast had lower appetite immediately before and after the exercise session, compared to those who exercised before eating. 

“It’s normal for blood sugar to increase after eating carbohydrate-containing meals,” says Alexa Govette, a PhD candidate in KPE who co-wrote the study  with Assistant Professor Jenna Gillen. “However, exaggerated spikes in blood glucose concentrations after eating are associated with increased risk for cardiometabolic diseases, like type 2 diabetes.”

While low-volume, high-intensity interval exercise has been shown to reduce the increase of blood sugar in laboratory settings, these protocols often involve specialized exercise equipment, says Govette. A novel aspect of this study was that the interval exercise protocol was equipment-free, consisting of only bodyweight movements such as jumping jacks, burpees and mountain climbers.

The timing of when you eat around exercise has also been shown to influence blood glucose concentrations and perceptions of appetite, but this has not been studied in the context of interval exercise or in an at-home setting. 

“To our knowledge, this is the first study to investigate how exercise-meal timing influences blood glucose responses to high-intensity interval exercise in females,” says Govette. “It is also the first study to assess the influence of exercise-meal timing on appetite perceptions in healthy females following bodyweight interval exercise.”

Govette says very few studies have examined the effects of exercise-meal timing in a female population, so this study in healthy young women provides much needed evidence for how blood glucose concentrations are influenced by the timing of exercise around meals. 

From a practical perspective, the study offers new insight into the effect of exercising around meals on blood glucose regulation and perceptions of appetite in an at-home/non-laboratory environment. 

“This study was conducted during the COVID-19 pandemic when research restrictions precluded us from conducting in-person exercise studies in our laboratory,” says Gillen. “In the end, this allowed us to investigate how the timing of exercise around meals influences blood sugar control in an at-home setting, which hadn’t been done previously.

“Given the growing popularity of at-home and virtual workouts, our findings may be of interest to individuals who prefer to exercise at home or those that do not have access to exercise equipment.”

Next, the researchers hope to investigate the effects of exercise-meal timing on blood sugar regulation in females who are at-risk or who are living with type 2 diabetes, given that exercise-induced reductions in blood glucose increases have more clinical relevance in these populations. 

“We currently have ongoing work that is comparing at-home bodyweight interval exercise to other forms of exercise in females with cardiometabolic risk factors to help address this question,” says Govette. “Additionally, it would be interesting to explore the influence of meal timing around bodyweight interval exercise over the course of several weeks to months, to assess the long-term effects on blood glucose regulation.”