Are morning workouts better for weight loss?

A new study suggests that what time of day a person chooses to work out might have an impact on their weight loss. 

There have been years of discussion about what time of day works best. Research and other studies have had conflicting answers, and medical weight loss physician Dr. Sue Decotiis told CBS News that really, the best exercise is whatever you can do. 

"What I tell my patients is work out when you can. If it's easier and more convenient for you to get to the gym in the morning, then go ahead and do that. If you can't get there until the afternoon, then do that," Decotiis said. 

The new study used a pre-existing National Health and Nutrition Examination Survey, which surveyed over 5,000 people from 2003 to 2006, to see what time of day the participants engaged in moderate-to-vigorous physical activity and whether they lost weight. Researchers observed a "strong linear association" between working out and lowered obesity for the group that worked out in the morning. People in the morning groups also had the lowest body mass index and smallest waist circumference, the study found. 

Participants in the morning groups had a mean 25.9 BMI and 91.5-centimeter waist circumference. Afternoon exercisers had a mean 27.6 BMI and 95.8-centimeter waist circumference, while people who worked out in the evening had a mean 27.2 BMI and 95-centimeter waist circumference. 

The morning groups also had the highest percentage of female participants, and those in the morning groups were older on average, though the BMI and waist circumference data controlled for those factors. Self-reported information about the participants' diets also showed that the people in the morning groups consumed fewer calories. 

Decotiis said that she wouldn't consider the study enough evidence to tell her patients to change their workout times. 

"I don't necessarily think that the evidence shows that you're going to burn more calories in the morning. Your ability to burn fat and to lose weight with exercise really depends on how well your insulin's working and how all your other hormones are working," she said, suggesting that people struggling to lose weight should consider talking to their physicians about their hormone levels, since they can impact how effective exercise and dieting are. 

The study's authors also said that more research was necessary. 

"The promising role of morning (moderate-to-vigorous physical activity) for weight management warrants further investigation," the study said. 

In:
• Health
• Exercise
• Weight Loss

Kerry Breen

Kerry Breen is a news editor and reporter for CBS News. Her reporting focuses on current events, breaking news and substance use.