Intermittent fasting has become an integral part of the nutrition and fitness world. Whether it's friends enthusiastically sharing their results, fitfluencers on social media, or athletes who swear by this way of eating, intermittent fasting remains one of the most popular dietary strategies right now. But what does this actually mean for people who exercise? And how do you combine this with healthy sports nutrition?

Intermittent fasting isn't so much about what you eat, but primarily about when you eat. Instead of eating throughout the entire day, you alternate periods of eating with periods of fasting. The idea is that during fasting, your body depletes its sugar reserves and then switches to burning fat.https://www.hopkinsmedicine.org/health/wellness-and-prevention/intermittent-fasting-what-is-it-and-how-does-it-workAlthough the concept itself has existed for centuries – our ancestors didn't eat constantly either – scientific interest in its benefits is relatively new.

What intermittent fasting schedules are there?

There are different ways to practice intermittent fasting, each with its own pros and cons. The most accessible form is the 16:8 method, where you fast for 16 hours and eat for 8 hours.https://health.clevelandclinic.org/intermittent-fasting-4-different-types-explainedFor example, you can eat between 12:00 PM and 8:00 PM, and fast for the rest of the day. Many people find this easy because a large part of the fasting period takes place during sleep. A slightly milder variation is the 14:10 method, where you fast for 14 hours and eat for 10 hours, for example, from 9:00 AM to 7:00 PM. This method is ideal if you want to start gently.

Additionally, there's the 5:2 diet, where you eat normally five days a week and restrict yourself to 500-600 calories on two non-consecutive days. The most intensive form is alternate day fasting, where you alternate daily between fasting days with minimal or no calorie intake and days where you eat normally.https://pierrehealth.com/intermittent-fasting-protocols-16-8-vs-5-2-vs-alternate-day-fasting).

What does science say?

Now for the most important part: what does scientific research say about intermittent fasting and athletic performance? The good news is that recent research is promising. A systematic review from 2024 concludes that intermittent fasting offers benefits for body composition without loss of muscle mass, and can even lead to improvements in maximal strength (https://pmc.ncbi.nlm.nih.gov/articles/PMC10780856/This is crucial for athletes who are afraid of losing muscle mass.

A study involving active women who combined intermittent fasting with high-intensity training showed a significant decrease in fat mass while maintaining muscle mass. This is precisely what many athletes are looking for. A recent meta-analysis examined the effects on athletic performance, such as maximum oxygen uptake and various forms of strength. The outcomes? Intermittent fasting doesn't appear to negatively affect athletic performance when carried out correctly.https://www.mdpi.com/2072-6643/17/12/1992).

More importantly: studies show that intermittent fasting and calorie restriction do not reduce the rate of muscle protein synthesis. This means your muscles can continue to grow and repair, even during fasting periods. At least, if you approach it smartly with sufficient protein intake.

However, an important point: these positive results come from studies lasting a few weeks to a few months. For the very long term (many months to years), questions remain, especially since a shorter eating window means fewer opportunities to consume protein. For now, however, the studies show that intermittent fasting can be combined well with sports, as long as you consume enough protein within your eating window.

The practical side: combining with sports

Combining intermittent fasting with exercise requires a thoughtful approach. Timing is crucial here. Plan your training sessions wisely: intense strength training or demanding endurance sports are best done within your eating window, or just before it. This way, you'll have enough energy for your workout and can recover well with nutrition immediately afterwards. Recent research from 2025 shows that the timing of meals is important: eating early in the day (early time-restricted eating) led to significantly more loss of belly fat and improved blood sugar regulation.https://pmc.ncbi.nlm.nih.gov/articles/PMC12035757/).

The dilemma of evening training

Here you arrive at a crucial point: what if you train in the evening, but your eating window closes at 8 PM? Your body needs recovery nutrition precisely after intensive training. This is where theory and practice clash. You then have a few options:

Option 1: Adjust your eating window. Do you often train in the evening? If so, shift your eating window to later in the day (e.g., 2:00 PM - 10:00 PM). This way, you can still eat after your workout.

Option 2: Train just before the end of your eating window. Plan your training so that you can still eat immediately afterwards. Training at 6:00 PM? Then you can have a recovery meal at 7:30 PM.

Option 3: Make a conscious exception. If recovery is important (for example, after strength training or intensive endurance sports), you can choose to eat something after your evening workout, even outside your fasting window. A protein shake or a small recovery meal might be more important for your athletic goals than strictly sticking to your fasting schedule.

The reality? For many athletes who are serious about strength or performance training, intermittent fasting works better with morning or afternoon training sessions. Do you train primarily in the evening and want optimal recovery? Then a traditional eating pattern might be more practical.

During your eating window, it's crucial to make nutritious choices. Opt for leafy green vegetables, healthy fats, lean proteins, and complex carbohydrates like whole grains. Your eating window is shorter, so every meal counts. Ensure you get enough protein within your eating window for muscle building and recovery. Distribute your protein intake across multiple meals within your eating window, aiming for 20-30 grams of protein per meal for optimal muscle protein synthesis.

During fasting periods, you can continue to drink water, black coffee, and unsweetened tea. Stay well-hydrated, especially around workouts. And don't jump in the deep end immediately: start with a 12:12 schedule, for example, and gradually build up to 14:10 or 16:8. Listen to your body and adjust where necessary.

Who does it work for and who doesn't it work for?

Intermittent fasting can be a useful strategy, but it is not for everyone. It can work well for recreational athletes looking to optimise their body composition, people who want structure in their eating patterns, and athletes in build phases who are primarily working on strength. However, be cautious or avoid it if you have a history of eating disorders, are pregnant or breastfeeding, have diabetes or other metabolic diseases (always discuss this with your doctor first), have multiple intensive training sessions per day, or are in a heavy competition period.

This is how you start

Start small and build up. First, choose a schedule that suits your lifestyle and training plan. Do you have early morning training? Then a later eating window might not be ideal. Do you prefer training in the evening? Then you can more easily stick to a 12:00-20:00 schedule. Keep an eye on your performance and energy levels. Do you feel weak or are your training sessions less effective? Then it's time to adjust the schedule. The goal is to make intermittent fasting work for you, not the other way around.

Do you have to do it every day?

A frequently asked question: do you need to do intermittent fasting every day? The short answer: no. You can also opt for a flexible approach, for example, by following an IF schedule 3-4 days a week and eating normally on the other days.

This can even have advantages:

• To persevere no daily pressure to stick to the schedule
• More versatile application – on busy days or social occasions, you just eat normally
• Less risk of stress You don't have to be perfect every day
• Still effective – even a partial application can yield results

Many people choose to follow their fasting schedule during the week and eat more freely at the weekend. Or they only apply it on quiet weekdays and not on days with intensive training or social activities. The most important thing is that it fits your life and goals. Intermittent fasting is a tool, not a dogma.

Intermittent fasting can offer benefits for body composition without negatively impacting sports performance, while maintaining muscle mass and even improving maximal strength. It is not a miracle cure, but it is a nutritional strategy that can work well for many athletes. The key is to apply it wisely: choose the right schedule for your situation, pay attention to the timing of your workouts, ensure sufficient quality nutrition within your eating window, and above all, listen to your body.

Intermittent fasting is a tool in your nutritional toolbox. No more, no less. Whether it works for you depends on your goals, lifestyle, and how your body reacts to it. Start cautiously, experiment, and see what works. And if you're in doubt? Discuss it with a sports nutritionist or your doctor.