Short bursts of intense exercise before meals may help control blood-sugar spikes better than one longer, less intense session, suggests a new small study.
Researchers say these "exercise snacks" may be an effective way to improve blood-sugar control among people with insulin resistance, a precursor to diabetes.
"Exercise spread across the day reduces sedentary time, and spread before meals reduces blood-glucose spikes after meals," said lead author Monique Francois.
"Exercise on top of an active lifestyle needs to be more intense than we normally do when walking or moving around," Francois, from the University of Otago in Dunedin, New Zealand, added.
She explained that exercise, along with insulin, stimulates muscles to take up glucose from the blood.
"Intense exercise [and prolonged exercise] … moves glucose into the muscle quickly and for several hours after," she said.
"Moving glucose into the muscle so it can be used as fuel or stored lowers blood glucose, as the body only wants a certain amount of glucose in the blood."
Francois and her colleagues studied two women and seven men diagnosed with insulin resistance. Two of the participants had type 2 diabetes, but none was taking medication for diabetes or blood-sugar control.
The participants completed three separate, one-day exercise programs in a random order.
The "exercise-snacks" program involved short bouts of intense exercise on a treadmill before breakfast, lunch and dinner. The composite exercise-snacks regimen was similar, but included some resistance exercises alternating with walking. The traditional continuous-exercise program consisted of 30 minutes of moderate-intensity walking before dinner only.
Meal timing and composition were the same during the three days.
The researchers found that the exercise-snacks and composite exercise-snacks routines controlled blood sugar more effectively than the continuous- exercise routine.
Specifically, there was a 17-per-cent reduction in glucose levels over the three hours following breakfast and a 13-per-cent reduction in glucose levels after dinner on the exercise-snack days compared to the continuous-exercise days.
Across the day, this represented a 12-per-cent reduction in average postmeal blood-glucose levels, the authors report in the journal Diabetologia.
This was a small study and more long-term studies need to be done to confirm the results. Francois said she'd also like to learn more about the best time for exercising and how to encourage people to exercise more.
She said high-intensity exercise can be performed in about half the time with similar or greater benefits than low- to moderate-intensity exercise.
"In this study, interval exercise using walking uphill or resistance-band exercises both improved glucose control similarly – the combination of resistance exercise to exercise the upper body and uphill walking targeting the lower body was chosen to maximize the muscle mass used," she said.
Francois added that cycling, walking and team sports have all been proven to be effective in helping to control blood-sugar levels.
Sheri Colberg-Ochs said the study's findings are "interesting … but not that surprising."
Colberg-Ochs studies diabetes and exercise at Old Dominion University in Norfolk, Va. She wasn't involved with the new research.
"My main issue with high-intensity intervals like that is that many people with diabetes (not just prediabetes, or insulin resistance) really aren't in any physical shape to undertake that type of exercise, and many of them have undiagnosed (or diagnosed) cardiovascular problems that may make such exercise unsafe for them to undertake as well," she said.
It's a risky activity for those patients that doctors would most want to help, Colberg-Ochs said.
"I would suggest instead that the walking be undertaken after eating to have a greater effect at suppressing postmeal rises in blood-glucose levels, in case some individuals cannot undertake the 'exercise snacks,'" she said.