Hot on the trail of the best way to optimize workouts for the quickest fat loss solutions, many people have turned to fasted workouts, or intermittent fasting. Fasted workouts have gotten a lot of attention for their proposed expedited weight loss, improved athletic performance and other potential health benefits. But could working out after a night’s rest—a potential 10- to 14-hour fast from the previous night’s dinner—really have enough benefits to outweigh a nutrient-dense pre-workout meal? 

What Are the Benefits of Fasted Workouts?

Fasted workouts typically mean jumping into a morning workout on an empty stomach. Research suggests that when you work out before breakfast, the reduced glycogen and insulin levels trigger energy utilization from the body’s fat storage instead of from food. After a meal is consumed, the pancreas produces insulin, a hormone that allows your body to use sugar (glucose) from carbohydrates for energy. Any unused glucose (glycogen) is stored in the body for later use. The theory behind eliminating a pre-workout meal is that without carbohydrates to burn for energy, stored fat in the body will be used instead, thus speeding up the potential for weight loss. 

One study focused on how exercising in the fasted state reduced the 24-hour energy intake for 12 active males. Energy intake is the number of calories consumed in a day. In addition to the decrease in calorie intake, the study also showed increased fat oxidation during exercise. This suggests that possible weight loss and weight management benefits could be reached through fasting. 

Another study focused on beneficial metabolic adaptions on fasted endurance exercise. This study separated 20 young men into two groups: one fasted and one fed an isocaloric carbohydrate-rich diet. Within the 6-week endurance-training program, the fasted group was able to increase exercise intensity and was more effective than the fed group at increasing muscular oxidative capacity while enhancing exercise-induced intramyocellular lipid breakdown. This is important for energy utilization in working muscles during exercise.

What Are the Disadvantages to Fasting Before Exercising? 

After an extended period of time without nourishment followed by exercise, the stress demands on the body are increased, energy output can be reduced, and it can lead to possible health risks. By not consuming a healthy pre-workout snack or meal, the body is in a state of nutrient debt, so-to-speak. This can lead to dizziness, weakness, fatigue or even fainting spells.

Intermittent fasting done regularly over time without sufficiently balancing out daily nutritional needs can also break down muscle and slow metabolic functioning. Severely restricting calories and beneficial nutrients on top of regular exercise can potentially lead to or exacerbate disordered eating patterns, increase vitamin deficiencies, lower immune functioning, trigger overtraining syndrome, or lead to other health conditions. 

It is not considered safe for people with the following conditions or factors to do fasted workouts or intermittent fasting: 

  • Pregnant or breastfeeding
  • Metabolic syndrome
  • Diabetes or hypoglycemia
  • Eating disorders
  • On prescription medication that needs to be taken with food
  • Deficient in electrolytes or dehydrated
  • Work out later in the day
  • Children, teenagers or people over the age of 55 

While there are many studies that suggest fasting offers health benefits, there are also studies that suggest there’s no difference between fasted or fed workout benefits. A study investigated changes in the fat mass and fat-free mass in young female subjects who were fasted or fed prior to aerobic exercise over a 4-week period of time. While both groups lost a generous amount of weight, the study conclusions showed no significant difference between conditions or measurements of the two groups who were either fasted or were fed. 

What Are the Benefits of Eating Before and After Exercise? 

1-2 hours before training, consuming a protein and carbohydrate-rich snack or meal balances blood sugar levels and elevates energy for workouts—especially as the intensity or duration of the workout increases. This can prevent the individual’s energy from dropping mid- or post-workout. Restricting calories for an extended period of time can also lead to over-consuming past the needed daily calorie intake later in the day, thus defeating much of the purpose of fasting.

Whether the workout was done fasted or fed, there is a post-workout window that should not be ignored. EPOC—or excess post-exercise oxygen consumption—usually occurs within an hour of exercise when the body is in debt of oxygen and ATP (adenosine triphosphate). What this means is that the body is in a state of recovery yet continuing to burn calories and use energy. Replenishing the body with protein snacks, meals or supplements will help rebuild muscles, balance blood sugar, recoup healthy nutrients and increase energy throughout the rest of the day. 

How to Manage Healthy Nutrient Intake and Exercise 

Whether an individual is choosing to fast or eat before workouts, it’s essential to maintain sufficient daily calories with a balanced diet of healthy proteins, carbohydrates and healthy fats.

 Good pre-workout fuel options:

  • Banana
  • Green apple with 1 tablespoon of nut butter
  • Slice of whole-grain toast with 1/2 avocado
  • Bowl of whole-grain cereal
  • Bowl of oatmeal

 Good post-workout fuel options:

There are many fasted workout and intermittent fasting protocols that promote safe exercise for weight loss and lead to improved athletic performance with a balanced nutrition program throughout the day. However, not everyone will benefit from fasted exercising or fasted exercising at increased intensities or durations. It may even pose a health risk to people with certain health conditions and those who do not continue balancing caloric and nutritional needs. Contact a physician for more information before fasting prior to exercise.