According to a study published March 2 in the Annals of Internal Medicine, obese people who exercised briskly for 40 minutes per day, four days per week, significantly improved not only their cardiovascular health, but also lost weight and reduced their blood sugar levels. In comparison, those who exercised at lower intensity improved their health and lost weight, but didn’t reduce their blood sugar level.
“Improvement at the higher intensity — just walking briskly on a treadmill — was substantially better,“ says Robert Ross, PhD, lead author of the study and an exercise physiologist at the School of Kinesiology and Health Studies at Queen’s University in Kingston, Ontario. “Participants were surprised at how easy it was to get to the higher intensity,”
About one-third of U.S adults over the age of 20 are considered obese, putting them at a much higher risk for cardiovascular disease. Exercise reduces that risk. Adults are currently advised by the federal government to exercise at moderate intensity for 150 minutes (2 hours and 30 minutes) per week or high intensity for 75 minutes (1 hour and 15 minutes) for the best health outcomes.
Intensity is measured by how hard a particular physical activity makes the cardiovascular system work, and it differs from individual to individual based on their level of fitness. For someone who isn’t fit, a brisk walk is enough to raise the heart rate to the optimal level for improving cardiovascular health. For someone who is fit, it takes a jog to get them to the ideal level, Ross says.
“Exercising at any intensity is good, whether it be a slower walk or brisk walk, but this study shows that if you want to improve all three — your waistline, your fitness level, and your blood sugar — then high intensity is your ticket,” Ross says.
The randomized controlled study, conducted between 2009 and 2013, monitored the physical activity and diet of 300 abdominally obese non-diabetic adults for six months. About two-thirds of the participants were women and one-third men. All had normal blood pressure.
The study broke the adults into four groups. One, the control group, was sedentary. A second group exercised at low intensity, for an average of 31 minutes per session. Another exercised at low intensity, for an average of 58 minutes. Another exercised at high intensity for 40 minutes. All of those in the three groups who exercised lost weight and improved their fitness. Only those in the high intensity group reduced their two-hour glucose levels. During the study, all participants ate a healthful, balanced diet (meaning 50 percent of calories from carbohydrates, 30 percent from fat, and 20 percent from protein), Ross says. The Canadian Institutes of Health Research funded the study.
“It’s an interesting study,” says Michael Emery, MD, medical director of the sports cardiology program at the University of South Carolina School of Medicine's Heart and Vascular Institute of Cardiology in Greenville. “It shows that you’ll get the biggest bang for your buck, in terms of cardiovascular fitness, if you run a mile at a high intensity rate, rather than walk a mile at a leisurely stroll.”
Whether the reduction in blood sugar levels in the high intensity participants was meaningful in terms of treating diabetes, Dr. Emery is less certain.
“It would have been interesting to know if the effect would have been more pronounced if there were a higher number of participants with high blood pressure or diabetes,” says Emery, who is also co-chair of the American College of Cardiology’s Sports Council. “It’s something where there could be more research.”
c/o Everyday Health
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