Intermittent fasting (IF) has become one of the most popular nutrition trends in recent years. Many people use it for weight loss or general health — and more athletes are now wondering whether fasting might improve performance, body composition, or recovery.

So… does it actually work?

Here’s a simple, evidence-informed look at how intermittent fasting affects strength, endurance, and overall athletic performance.

How Does Intermittent Fasting Affect Athletic Performance?

Research on fasting and performance is mixed — and sometimes contradictory — because different studies use different fasting schedules.

Here’s what we know so far:

1. High-Intensity Performance Often Decreases

Sports requiring:

• sprinting

• repeated explosive efforts

• power output

• speed

tend to suffer when carbohydrates are limited before training.

Athletes in studies often experience:

• reduced peak power

• quicker fatigue

• slower reaction time

This effect can last days to weeks depending on the fasting protocol.

2. Endurance Performance Shows Mixed Results

For steady, low-to-moderate intensity efforts:

• Some studies show no major change.

• Others show a slight decrease in performance.

The difference often comes down to:

• whether the athlete consumes carbs during the eating window

• whether training occurs deep in the fasting period

• total energy intake

Fasting does not appear to improve endurance performance.

3. Strength Training Is Mostly Unaffected

Resistance-trained athletes in several studies:

• maintained muscle mass

• maintained strength

• reduced body fat

As long as:

• total daily protein is sufficient

• calorie intake remains adequate

• training occurs during the eating window

Notably, fasted strength training may reduce performance if low energy availability becomes an issue.

4. Intermittent Fasting May Help Athletes Reduce Body Weight

Some athletes need to make weight for competition (combat sports, rowing, powerlifting). IF can help with:

• reduced appetite

• simplified meal timing

• lower calorie intake

• potential reduction in body fat

However, athletes must be careful:

Low energy availability can impair recovery, strength, hormones, and overall performance.

Who Might Benefit From IF?

Intermittent fasting may be helpful for:

• athletes needing long-term, manageable weight control

• recreational athletes interested in simplicity

• people who prefer fewer meals

• athletes training mostly at moderate intensities

It may NOT be ideal for:

• sprinters

• heavy strength athletes

• team sport athletes

• athletes training twice per day

• individuals prone to low blood sugar

Important Considerations for Athletes

If you choose to try intermittent fasting:

✔ Time your eating window around training

You will feel and perform better with fuel available before intense sessions.

✔ Prioritize protein

Aim for consistent protein intake across the eating window.

✔ Ensure enough total calories

Under-eating reduces performance more than any eating schedule.

✔ Monitor recovery

If you feel unusually fatigued, sore, or weak — fasting may be impairing recovery.

Bottom Line

Intermittent fasting is not a performance booster, but it can be a useful tool for certain athletes — especially for weight management. Its effects on strength and endurance are mixed, and results depend heavily on training demands and overall calorie intake.

As with all nutrition strategies, the best approach is the one you can maintain while still performing well, recovering effectively, and feeling healthy.