What’s the Best Time of Day to Exercise?

CU Anschutz researcher answers common questions about exercise and weight loss

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Written by Kiley Kudrna on November 17, 2022
What You Need To Know

Seth Creasy, PhD, discusses the optimal time of day for exercise and other weight-loss strategies.

With the holidays around the corner, you may be wondering when is the best time to schedule your exercise routine during a hectic time of the year. Seth Creasy, PhD, assistant professor of endocrinology at the University of Colorado School of Medicine, answers questions about exercise, diet and sleep and talks about a new clinical trial targeting the question: What time of day is best to exercise?

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If you work out in the morning, should you eat breakfast before or after exercising?

This depends on what you are hoping to get out of your exercise routine. There's not much data in the area of morning versus evening exercise while also examining the effect of fasted versus fed exercise.

The few studies that have been completed suggest that if you exercise in the morning before breakfast, you actually burn more fat during the exercise and that actually lasts for about 24 hours. What's unknown at this point is whether that actually translates into fat loss over time. We need a longer-term study to see what the clinical implications are of fasted versus fed exercise at different times of the day.

What role does a good night’s sleep play in weight loss?

One of my areas of research is looking at the importance of sleep and weight management. I think sleep is the often-forgotten pillar of health, along with diet and physical activity. I think it's because as a society we're so focused on what can we get done in 24 hours that we forget how important sleep is and how it actually supports us during the day when we're awake.

This is particularly true for weight management. Sleep not only directly affects our metabolism, but it also influences our food choices and our physical activity behavior. If you're not sleeping well, it's more likely that you're going to make poor dietary food choices. Similarly, if you're not sleeping well, it's hard for you to engage in exercise because you're tired.

I think engaging in healthy sleep behaviors – like getting seven hours of sleep or more, going to bed and waking up at consistent times, trying to minimize external light in the evening – all of those may have both direct effects on weight management and indirect effects on food choices and physical activity behavior.

Is counting calories essential to weight loss – why or why not?

If you poll the people who are in our weight-loss programs, they say counting calories was one of the most important factors for their weight loss. However, they also report that they're not likely or willing to continue doing it because it's so difficult to do long term.

That's one of the issues with counting calories. That's where new dietary strategies like intermittent fasting and/or time-restricted eating come into play. Intermittent fasting and time-restricted eating are strategies to reduce your calories or cut calories without as much effort of counting calories. If you're doing alternate-day fasting, which is a popular strategy where one day you completely fast or you only take in maybe 500 calories, and then the next day you eat as much as you want. Then you keep cycling back and forth between fasting and eating. There's data to suggest that essentially helps reduce your caloric intake.

Same thing for time-restricted eating. Instead of counting your calories, you restrict your eating window to eight or 10 hours across the day. And by doing that, you're reducing your caloric intake because you can only take in so many calories in that eight- to 10-hour window. I think ultimately, at the end of the day, the goal is to reduce caloric intake if you want to lose weight. Counting calories, intermittent fasting and time-restricted eating are all strategies to do that.

With regards to Thanksgiving, if you're going to eat a large meal at lunch or dinner, you could try to fast or limit food intake on the day before Thanksgiving and then on Thanksgiving say, “Hey, I'm just going to eat today.” Or you could limit your intake earlier in the day on Thanksgiving knowing that you're going to eat a larger meal for lunch or dinner.

Does stopping eating early in the evening lead to more weight loss?

Another really interesting area of research right now is looking at these time windows and when to eat during the day. With time-restricted eating, for example, you're restricting the eating window to eight to 10 hours, but you can do that early in the day or you could do that late in the day. As you could imagine, if somebody wakes up at 8 a.m. and they only eat until 4 p.m., that would be early time-restricted feeding. And late time-restricted eating would be eating from noon to 8 p.m.

The bulk of observational studies suggest that late eating is associated with poor metabolic health outcomes. When you're consuming more calories in the evening, this may impair weight loss efforts. So the hypothesis is that earlier time restricted eating would be more beneficial for weight management, but we're just starting to see some of these studies coming out now.

What are the pros/cons to exercising later in the day?

I'm biased, but I don't like to highlight any cons to exercise because the benefits far outweigh the cons. In general, what I tell people right now is: Choose to exercise at a time that you're likely to adhere to long term. If you're going to pick something that you're not enjoying and you can't do long term, then it's not going to be effective long term. If you hate getting up to exercise in the morning and you're miserable, even if that's the most beneficial time, if you're not going to do it long term, then I don't think morning exercise is the way to go.

As far as health benefits, I think we're still trying to figure out what time of day is best. We may be able to enhance or optimize certain health benefits by exercising at different times of the day. But again, I want to emphasize that you're getting benefits no matter what time of day you exercise.

Losing weight and keeping it off is difficult. How do you help people to lose weight and maintain it long term?

To be honest, it's a paradigm shift for people who are in our weight-loss programs. Everybody wants to know, “What's the cure? How long do I have to do it? And then I'm done.” But it's not that. It's a lifestyle change or a long-term change. You're never done. So, the question is what can you do now to help you lose weight and what can you continue doing? Because if you're not going to continue with your lifestyle changes, your weight is going to creep back up. Your physiology is working against you, and it’s an uphill battle.

It's hard to lose weight. It's hard to maintain it. But we try to promote and support weight-loss efforts through lifestyle strategies that can be maintained long term.

Can you discuss the clinical trial you are working on at the Anschutz Health and Wellness Center?

Right now, we have a clinical trial led by Victoria Catenacci, MD, in the Anschutz Health and Wellness Center. It's designed to answer the question: What time of day is best to exercise for weight loss? We are randomizing individuals who are overweight or obese to exercise in our fitness center in either the morning or the evening. And they will do this for 13 months. We're looking at how morning and evening exercise affect body composition, and also how they affect energy expenditure, energy intake, meal timing and sleep. And we're hoping that this study can help us to make better recommendations about exercise at different times of the day. We're currently enrolling subjects for this study and will continue to do so over the next couple of years.

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Seth Creasy, PhD