Should You Work Out Without Eating First? Here’s What You Should Know

Working out is a great way to support your 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 has more health benefits than working out in a fed state. Some research suggests that exercising on an empty stomach can improve insulin levels and help you burn fat.

However, fasted workouts have not proven more effective for weight loss than fed workouts. Exercising in a fasted state can also come with risks for pregnant people or people with diabetes. So, how do you know if a fasted workout is right for you?

Fasted workouts refer to exercise on an empty stomach. If you’ve been fasting for several hours before exercising, your workout is fasted.

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

Yes, but it’s not that simple.

Working out on an empty stomach may lead your body to burn fat for fuel instead of carbs. If you’ve fasted for around 12 hours, like an overnight fast, your body’s glycogen (sugar) stores are depleted, forcing 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 overall weight loss or calorie burning.

Multiple studies have found no significant differences in weight loss or body shape between people with a fasted workout routine and people with a fed workout routine.

Some research suggests that working out while fasting may be more effective for reducing insulin levels than fed workouts.

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.

In one study of men with overweight and obesity, men who completed fasted treadmill workouts five days a week for six weeks saw lower fasting insulin levels than those who completed fed workouts. They also saw greater improvements in insulin resistance compared to men who exercised after breakfast.

Based on these findings, some researchers suggest that exercising while fasting may be helpful for people with diabetes and insulin resistance. However, more research is needed to understand how fasted exercise affects insulin levels and whether or not it should be recommended for people with diabetes. 

Exercise lowers your blood sugar levels. Because of the risks of hypoglycemia (low blood sugar), fasted workouts may not be suitable for people with uncontrolled diabetes, people on certain blood sugar-lowering medications, and people who experience frequent low blood sugar.

Fasting can also pose risks for people who:

• Are pregnant
• Are under the age of 25
• Take insulin or other medications for diabetes
• Have a history of seizures
• Work at night
• Operate heavy machinery
• Have been prescribed medications that must be taken with food

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

• They leave you hungrier: One review found that hunger levels were significantly higher during fasted exercise than when people exercised while fed.
• They may increase fatigue and cortisol levels: Some research suggests that fasting before aerobic exercise may increase fatigue (tiredness) and cause your body to release more cortisol (the stress hormone). High cortisol can suppress your immune system, promote belly fat, decrease your insulin sensitivity, increase your risk of osteoporosis and hypertension (high blood pressure), and reduce muscle mass.
• They may burn fewer calories: One review found that participants burned fewer calories throughout the day after a fasted workout than when they had eaten before working out.

Some studies suggest that fasted workouts can help you burn fat and improve your insulin sensitivity. However, there isn’t much evidence that fasted workouts are significantly better for you. Fasted workouts aren’t more effective for weight loss than working out in a fed state. They might also increase fatigue and cortisol levels and burn fewer calories than fed workouts.

Working out on an empty stomach isn’t safe for everyone. A healthcare provider can help you decide whether it’s safe to try. If you’re interested in trying a fasted exercise routine, consider starting with a short, low-intensity workout to ensure it’s the right choice for you.