This 2-hour workout window maximizes your weight loss, experts say

As obesity rates continue to climb worldwide, experts are zeroing in on physical activity as a key tool for weight control. Regular movement doesn’t just help manage weight—it also lowers the risk of chronic disease and early death. But despite broad agreement on its value, the debate still lingers over one detail: when is the best time to exercise?

Several studies suggest that workout timing might make a difference. One analysis from the Women’s Health Study looked at accelerometer data and found a striking trend. Women who did less of their daily activity in the morning showed a higher risk of obesity—even after accounting for total activity levels.

Meanwhile, other researchers point to the evening as the ideal window for exercise. One study linked evening workouts with lower body mass index (BMI), suggesting they may be more effective for maintaining a healthy weight. These conflicting findings leave the fitness world without a clear consensus.

Digging deeper, scientists are turning to the body’s internal clock for answers. Known as circadian rhythms, these natural cycles govern metabolism, insulin sensitivity, and energy use. Our bodies follow a daily rhythm that influences how we burn calories and store fat, depending on the time of day.

This timing effect is especially visible among shift workers. Their disrupted schedules often throw off circadian rhythms, putting them at greater risk for obesity and metabolic problems. These patterns show that timing could matter just as much as the activity itself.

Controlled lab studies are beginning to shed light on the issue. Morning exercise—especially on an empty stomach—has been shown to increase fat oxidation more than evening workouts. That means more fat is burned when glycogen stores are low, a state triggered by overnight fasting.

In fasted conditions, the body is more likely to tap into stored fat for fuel. This shift not only boosts fat burn but may also reduce overall calorie intake throughout the day. Early morning workouts, done before breakfast, could offer a unique advantage for those trying to lose weight.

However, studies on appetite control following exercise present mixed results. While some research supports the idea that morning exercisers experience a reduction in subsequent energy intake, other studies show no significant differences between morning and evening exercise in terms of post-exercise appetite suppression.

The overnight fast is a key factor that differentiates morning exercise from workouts done later in the day and may contribute to its effectiveness for weight management.

Accelerometers are commonly used to measure physical activity, yet most studies have focused on frequency, intensity, and duration rather than the timing of physical activity throughout the day. The influence of accumulating physical activity at different times on obesity is still largely unexplored.

Moreover, it’s not clear whether adhering to physical activity guidelines—150 minutes per week of moderate-to-vigorous physical activity—at different times of day provides equal benefits in reducing obesity risk.

Dr. Natalie Azar, NBC News medical contributor, summed up the debate by stating, "The best time to exercise is when you can fit it in for sure. If first thing in the morning is your jam, by all means keep on doing it." She emphasized that the specific timing might depend on personal goals.

Recent research suggests that evening workouts might be better for managing obesity and blood sugar levels. But no matter when you exercise, the health benefits are significant, including enhanced cardiovascular health and muscle strength.

Morning exercise is often the easiest time for people to fit fitness into their schedules. Many experts agree that early morning workouts can provide various benefits, especially for weight loss.

A 2023 study published in the journal Obesity analyzed data from over 5,200 participants and found that moderate to vigorous exercise between 7 a.m. and 9 a.m. was linked to a lower BMI compared to exercising at other times of the day.

Morning exercisers tended to have healthier habits overall—they were more likely to avoid tobacco and alcohol, exercise consistently at the same time each day, and consume fewer calories compared to those who exercised later.

Tongyu Ma, the lead researcher of the study from The Hong Kong Polytechnic University, cautiously suggested that exercising early in the morning before eating might lead to more weight loss than workouts at other times.

However, Cameron Mitchell, a kinesiology expert at The University of British Columbia, urged caution, noting that the study's findings did not conclusively determine that morning exercise alone led to "optimal health." It’s possible that the other health-conscious habits practiced by morning exercisers played a significant role in these outcomes.

Morning exercise may also prompt biological benefits linked to circadian rhythms. For example, research suggests that exercising early may help reset the body’s molecular clock, which in turn can boost metabolic health and assist with weight loss.

Additionally, people who naturally wake up earlier tend to squeeze in more exercise compared to those who stay up late. A study in Finland found that early risers managed about 30 minutes more of physical activity daily for men, and about 20 minutes more for women, than their night-owl counterparts.

Exercising early can also help people feel accomplished, which has positive psychological effects. According to Jack Raglin, an exercise psychologist, morning workouts can provide a mood boost and give a sense of accomplishment, which can positively impact the rest of the day. Morning exercise also releases endorphins, the body's natural "feel-good" chemicals.

For those who want to burn more fat, exercising on an empty stomach before breakfast might be a good strategy. A 2019 study found that participants who exercised after an overnight fast burned twice the amount of fat compared to those who worked out after breakfast. They were also better at controlling their blood sugar levels, and adapted well to early exercise routines.

Javier Gonzalez, a co-author of the study and senior lecturer at the University of Bath, pointed out that exercising before breakfast isn’t for everyone. People with diabetes on insulin treatment, for instance, could face a higher risk of hypoglycemia if they exercise without eating. For healthy individuals worried about lacking energy for early workouts, Gonzalez suggested a cup of strong black coffee before exercising to make the session feel easier.

While morning workouts are frequently recommended for their practical and physiological benefits, it’s important to remember that exercising at any time of day is still beneficial for overall health. For example, evening exercisers may find it easier to combine strength training with cardio workouts since they are already warmed up from the day's activities.

Ultimately, the best time to work out is the time that fits best into your schedule. Whether you prefer to exercise early in the morning or late in the evening, staying active is crucial for both physical and mental well-being. What’s most important is consistency and choosing a time that allows you to form and maintain a regular habit.

Physical activity, at any time of day, provides a wide range of health benefits—so finding a routine that works for you is key to reaping these rewards.

Note: Materials provided above by The Brighter Side of News. Content may be edited for style and length.

Like these kind of feel good stories? Get The Brighter Side of News' newsletter.