People trying to lose weight, or at least prevent gaining it, are wise to turn to exercise. Burning calories — along with reducing the consumption of them — is the best way to reduce the risk of obesity. There is something else, too: They may be able to get more of a return on their exercise investment by exercising early in the day.
The finding comes from a recent study that looked at whether people who get the recommended 150 minutes of moderate-to-vigorous physical activity every week can reduce their risk of obesity depending on the time of day they are most active.
It turns out that when people exercise strongly affects the benefits they get from exercise and their risk of obesity. Researchers from Franklin Pierce University, Hong Kong Polytechnic University, and Arizona State University found that the best time of day for physical activity is early: between 7 and 9 am. That’s when you are likely to get the most benefit from exercise in terms of keeping your weight under control.
“These findings suggest that the daily pattern of moderate-to-vigorous physical activity can be another important aspect of the complexity of human movement,” one of the authors on the study, Tongyu Ma, told TheDoctor.
“A morning workout can promote fat burning even after the workout is over, which can make time spent being sedentary during the rest of the day less detrimental.”
Data from almost 5,300 people who participated in the National Nutrition and Health Examination Survey in 2003-2004 and 2005-2006 were used for the study. Participants were grouped into morning, midday and evening clusters, based on readings from the accelerometers they wore indicating at what time of day they got the most physical activity.
People in the morning cluster had a spike of physical activity between 7 am and 9 am, and lower activity levels during the rest of the day, suggesting they worked out in the morning. The midday cluster was increasingly active during regular working hours — 9 am to 4 pm — with peak activity levels between 11 am and 1 pm.
Those in the evening cluster had a steady increase in activity levels between 7 am and 5 pm, with peak activity levels between 5 pm and 8 pm, followed by a rapid decrease in activity between 8 pm and midnight.
People in the morning cluster who met the physical activity guidelines had a lower body mass index and waist circumference compared to those in the other clusters who met the guidelines. Based on what participants said they ate, those in the morning cluster also had a healthier diet and ate fewer calories per unit of body weight.
Surprisingly, participants in the morning cluster were about 10- to 13-years older than those in the other groups. They were also more likely to be white, have a college or advanced degree and not use tobacco or alcohol. The morning cluster also had the highest percentage of women.
Among those who engaged in moderate to vigorous physical activity in the morning, as their amount of activity increased, body mass index and waist circumference decreased.
In contrast, among those who were physically active at midday and in the evening, body mass index and waist circumference decreased at first as the amount of activity increased, but then remained steady. One possible reason BMI improvements stalled out among these groups, said Ma, a research assistant professor at The Hong King Polytechnic University, is that their energy consumption — the calories they took in during the rest of the day — went up. “When people exercise more they tend to eat more, which offsets the benefits of exercise.”
People in the morning cluster still had a lower BMI and waist circumference than those in the other groups, even though they were sedentary for longer periods of time. The reason? “A morning workout can promote fat burning even after the workout is over, which can make time spent being sedentary during the rest of the day less detrimental,” Ma explained.
“We are currently starting a clinical trial to compare morning versus evening exercise for weight management,” said Ma. Stay tuned, and keep exercising at whatever time of day seems to work best for you.
The study is published in the journal Obesity.