Fasted or Fed: Which Is Better for My Workouts?

One of the benefits of working out on in a fasted state is the noticeable improvement in insulin sensitivity. (Image: Gary Burchell/Digital Vision/Getty Images)

A “fasted” state means a person has not consumed any food before an exercise session, while a “fed” state means a person has had some form of fuel like carbohydrates, protein or fat ingested before hammering out a workout.

Working Out On an Empty Stomach

Young woman stretching her leg on a wall at sunset
Working out while in a fasted state can also help ensure nutrients are distributed efficiently and minimize accumulation of body fat. (Image: lucapierro/RooM/Getty Images)

One of the most apparent benefits of working out on in a fasted state is the noticeable improvement in insulin sensitivity. When we eat, the body releases insulin. This hormone then helps move the sugars from our bloodstream into our organs like the liver and muscles.

Poor insulin sensitivity happens when we eat too often, putting our blood sugar on a roller coaster of flux, in turn making us more resistant to the effects of insulin in the long term. It also makes it harder to lose fat. When the body is in a fasting state, it releases insulin less regularly, thus making us less sensitive to insulin and heightening our opportunity to lose fat.

Another benefit of training in a fasted state is the increase in human growth hormone (HGH). In tandem with proper sleep and a regular workout schedule, growth hormones help with building new muscle tissue, burning fat and improving bone quality and physical functions. Fasting has been shown to increase the human growth hormone up to 1,300 percent in women and 2,000 percent in men.

Working out while in a fasted state can also help ensure nutrients are distributed efficiently and minimize accumulation of body fat. Testosterone levels go up when we work out, helping build muscle tissue and improve energy levels. Together with growth hormones, these two combinations are a great way to build lean muscle as the spike in growth hormones help burn fat. Studies have also shown that while fasting, people progressively burn fat better at higher levels of intensity.

However, there are instances in which fasting before exercising impaired the performances of athletes, but this was mostly due to Ramadan fasting, which also prohibits liquid consumption. Another study also shows that in the first 90 minutes of exercise, the amount of fat burned was the same regardless if you ate beforehand or not.

Only after the 90-minute mark did subjects who fasted show any results, meaning you’d need to exercise for hours to get any significantly better results. In some studies, no significant changes in body composition or body fat were detected when a meal-replacement shake was provided before an aerobic exercise for a fed-state group and right after an aerobic exercise for a fasting-state group.

Exercising in a fasted state also increases the amount of protein tissues burned for energy, sometimes exceeding 10 percent of the calories burned — double that if you exercised in a fed state.

Exercising in a fasting state also helps boost muscle glycogen storage efficiency. Occasionally fasting helps the body adapt to using available fuel in the body. Then when you actually perform a workout in a fed state, your performance will be much better. Notable improvements are a person’s maximal oxygen consumption (VO2 Max), an integral part for endurance athletes used to measure the maximum volume of oxygen a person can take.

Working Out On a Full Stomach

Fitness trainer keeping time with woman doing dumbell push-ups
When working out in a fed state, you can perform higher-intensity exercises for longer. (Image: Westend61/Westend61/Getty Images)

When working out in a fed state, you can perform higher-intensity exercises for longer due to the body’s need for energy, resulting in better muscle gains. The more carbohydrates you burn while exercising, the more fat you burn post-workout and vice-versa. The body needs energy to work, and eating before exercise increases excess post-exercise oxygen consumption (EPOC).

EPOC is the number of calories burned during a post-workout period. Most of the calories we burn come from fat. Meaning during post-workout, more fat is burned as opposed to during exercise. Fat burning should be seen as a process that takes into account the total amount of fat burned in days after the workout as opposed to only during and immediately after the workout.

Eating before exercise also results in consumption of fewer calories later in the day. This is probably due to the efficiency of the body in using the absorbed nutrients from the carbohydrates. Fat burning is also negligibly lower compared to those who fast before working out. Amino acids are still released throughout the day, even after digesting nutrients in a fed state. Research has shown that people who consume complex carbohydrates before a workout in the morning have much less total caloric intake for the whole day.

Bottom line, there’s no right or wrong position: Different people have different needs. So working out, whether in a fasted or a fed state, all depends on how your body responds and which feels more comfortable. There are many factors that contribute to how your body works, so what works for you may not work for others. Experiment, listen to your body and make adjustments accordingly — after all, you know yourself better than anyone else.


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