Working out supports physical and mental health. It can help you lose weight, gain muscle mass, and reduce the risk of conditions like heart disease and depression.

Some people wonder if working out while fasting is better than working out in a fed state. Fasted workouts refer to exercising on an empty stomach. Some research suggests that fasted workouts may offer some benefits, but there are a few potential downsides. 

Fasting is abstaining from eating for a specific time period. There is no official definition for a fasting window, but most studies that have investigated the effects of fasted workouts have used fasting windows of at least six hours.

Studies show that working out in a fasted state could offer some health benefits like supporting fat burning and improving insulin levels. 

May Enhance Fat Burning 

When you exercise while fasting, your body breaks down fat for fuel instead of carbs. If you’ve fasted for around 12 hours, like an overnight fast, your body’s glycogen stores are depleted, which forces you to break down fatty acids for energy.

Some studies have shown that exercising in a fasted state burns more fat than exercising in a fed state. However, fasted workouts haven’t been shown to be more effective for weight loss or calorie burning.

One study found no significant differences in weight loss or body shape in men with overweight and obesity who did either non-fasted or fasted treadmill workouts five days a week for six weeks. Another review found no significant difference in weight loss when comparing fasted versus fed exercising.

May Reduce Insulin Levels and Improve Insulin Sensitivity 

Insulin is a hormone that helps blood sugar enter cells. Insulin resistance is a condition in which cells stop responding to insulin effectively, leading to high blood sugar levels.

Having high insulin levels can increase the risk of conditions like obesity, type 2 diabetes, and heart disease. Working out while you’re fasting may be more effective for reducing insulin levels than fed workouts.

In one study of men with overweight and obesity, men who did fasted treadmill workouts five days a week for six weeks saw lower fasting insulin levels. They also saw improvements in insulin resistance compared to men who exercised after breakfast. Therefore, some researchers suggest that exercising while fasting may be helpful for people with diabetes and insulin resistance.

More research is needed to understand how fasted exercise affects insulin levels and whether or not it should be recommended for people with diabetes. 

There are a few potential downsides to fasted workouts. For example:

• One review found that hunger levels were significantly higher during fasted exercise than when people exercised while fed. The review also found that participants burned fewer calories throughout the day after a fasted workout than when they had eaten before working out.
• Fasted workouts may not be appropriate for people with uncontrolled diabetes, people on certain blood sugar-lowering medications, and people who experience frequent low blood sugar.
• Some research suggests that fasting before aerobic exercise may increase fatigue and cause your body to release more cortisol (the stress hormone). High cortisol can suppress your immune system, promote belly fat, decrease insulin sensitivity, and decrease muscle mass.

Some people think that fasted exercise is better than exercising in a fed state. However, there isn’t much evidence that fasted workouts are significantly better for you.

Some studies show that fasted workouts may increase fat burning and may improve insulin sensitivity. However, fasted workouts aren’t more effective for weight loss than fed workouts. Working out while fasting might also increase hunger levels and reduce calorie burning, and it isn’t appropriate or safe for everyone.

If you’re interested in fasted exercise, start with a short, low-intensity workout to ensure it’s the right choice for you.