EVERY MORNING, GYMS throughout the country are packed with exercisers determined to rise and grind, and squeeze in an early workout to meet their weight-loss goals.
That’s because traditionally experts have argued that when you exercise first thing in the morning – especially prior to eating breakfast – your body is more apt to burn fat. And when you’re trying to lose weight, your primary goal is losing fat.
Why would exercising first thing in the morning help you burn more fat? Because the body’s preferred, most fast-acting energy source is carbohydrates, found in the blood as glucose and stored in the liver and muscles as glycogen, explains Hayden Steele, an Oklahoma City-based personal trainer and certified strength and conditioning specialist. Here’s how the theory works: In the morning, when your glucose and glycogen levels are depleted, your body is forced to instead use your body fat to power your workout.
Case in point: A 2010 study published in the Journal of Physiology, in which men were instructed to increase their calorie and fat intake, found that the 10 men who exercised before breakfast burned more fat than 10 others who exercised mid-morning after already eating. “This study for the first time shows that fasted training is more potent than fed training [at burning fat]” and improving the body’s ability to regulate blood sugar levels, the researchers concluded.
However, since then, researchers have learned that the fat-burning strategy is not that simple. The most recent meta-analysis of fasted exercise on weight loss, published in 2017 in the Journal of Functional Morphology and Kinesiology, found that any effects were “trivial” after combing through the available data.
“I’m not citing one study as conclusive evidence,” Steele says. “There is surprisingly a very small amount of studies on this topic, so we can only draw conclusions from what we have. But this study is significant because it’s the first-ever systematic review of fasted versus non-fasted cardio. So, it carries a lot of weight.”
But even if the body does burn a greater percentage of calories from fat versus carbohydrates during fasted exercise, it will still likely burn fewer total calories, including those from fat, says Ryan Campbell, a training specialist at Anytime Fitness of Southern Wisconsin. And even if your rate of perceived exertion, or how hard you feel that you’re working, is intense, your body is physiologically not able to perform as intensely in a fasted versus fueled state.
But all fasting (or not) aside, there are some legitimate benefits to exercising in the morning.
Levels of testosterone – a hormone that has been linked to fat loss, muscle gain and thus increased metabolic rates – is high in the morning and declines throughout the day, Steele says. And a 2014 Medicine & Science in Sports & Exercise study found that intense morning strength training sessions can help keep levels higher throughout the day.
Meanwhile, in a previous 2012 study also published in Medicine & Science in Sports & Exercise, when women walked briskly in the morning for 45 minutes, they automatically were less distracted by images of food and also increased their activity levels throughout the rest of the day.
“For many people, exercising in the morning sets them up for success the rest of the day,” Steele explains. “It’s the domino effect.” By exercising in the morning, he says, you increase your levels of feel-good hormones and neurotransmitters that improve energy levels, self-esteem and mood – all contributing to healthier decisions that lead to weight loss.
What’s more, “getting exercise done prior to the start of a busy day will help ensure it does not become a task that gets overlooked on the daily agenda,” Campbell says.
Why You May Want to Work Out in the Afternoon or Evening
“If you’re someone who lacks energy in the mornings or exercise simply doesn’t ‘fit’ into the morning, that’s OK,” Steele says.
After all, the body may be physically primed to put in the best, most effective workouts later in the day, thanks to the body’s natural circadian rhythms. For example, in a series of 2009 studies of soccer players published in Chronobiology International, both internal body temperature and athletic performance peaked between 4 and 8 p.m. They also noted that energy was the highest and fatigue the lowest at 8 p.m.
“Every person has a circadian rhythm typically peaking and falling two times per day,” Campbell says. The National Sleep Foundation explains that adults’ greatest drives to sleep occur between 2 and 4 a.m. and 1 and 3 p.m., though each person’s circadian rhythms are unique. “Working out around those peaks is ideal as a person would have a more successful workout,” he says. “Too many times, people go to the gym but end up doing very little to challenge their bodies to change.” But when we work out at the times of day that we have high energy levels and feel our best physically, we are more likely to challenge ourselves and reap more significant exercise results, he says.
Meanwhile, post-dinner exercise has its own unique benefits. For instance, a 2013 Diabetes Care study links post-meal walks with improved blood sugar regulation. While getting in some movement after every meal is ideal, most Americans tend to make dinner their largest meal and stay sedentary (and snack) following dinner, Campbell says. So an after-dinner workout could theoretically spur greater changes in overall energy expenditure than a post-breakfast or post-lunch workout could.
Still, it’s important to pay attention to your individual circadian rhythms to ensure that your workout isn’t so late that you’re already worn out from your day or that it doesn’t prevent you from falling asleep come bedtime. While exercising close to bedtime could potentially increase energy levels and impede sleep, there isn’t a clear consensus – and a 2011 study in the Journal of Sleep Research found that exercising 35 minutes before bed did not decrease sleep quality. In short: The body’s timing is individual.
The Best Times of Day to Work Out
“If I had to sum up my answer for the general population as to ‘What is the best time to exercise?’ My answer would be quite simply, ‘When you can fit it in your schedule!'” Steele says. “‘If that’s in the morning, great. If that’s at lunch, fantastic. And if you have time in the evenings, awesome.’ Adherence is everything.”
After all, 2013 research published in the scientific journal Appetite concluded that feeling as though you are able to exercise – despite barriers such as time constraints – is a significant determiner in one’s ability to successfully lose weight. And consistency is critical to weight-loss results.
“In the grand scheme of things, workout timing has little relevance in most people’s weight-loss success,” Campbell says. “What is more important than trying to lose weight with minutia strategies is getting an efficient and effective workout in.” Ultimately, whenever you can get the most out of your workout is the best time for you.