Intermittent fasting has become one of the most talked-about approaches to eating, but what does it actually involve – and can it support your training and nutrition goals?
Unlike traditional diets that focus mainly on what you eat, intermittent fasting is centered around when you eat. By alternating between periods of eating and fasting, it can offer a simple framework that some people find easier to follow. However, it isn’t a shortcut to better health or faster results, and it won’t be the right approach for everyone.
In this guide, we’re breaking down how intermittent fasting works, the different approaches you may have heard about, and what the research tells us about its potential benefits – both for a healthy diet, and as part of a sustainable workout routine.
What is intermittent fasting?
Intermittent fasting is an eating pattern that alternates between periods of eating and periods of fasting. Rather than focusing on cutting out or demonizing particular foods or food groups – or fastidiously breaking down a nutrition label every time you’re at the grocery store – intermittent fasting is mainly about when you eat.
In a sense, everyone fasts naturally while they sleep. Intermittent fasting simply extends that window by creating a longer period between your last meal of the day and your next one.
There are several ways to approach intermittent fasting1, ranging from relatively gentle overnight fasting windows to more structured plans that limit eating to certain hours or days. The key thing to remember is that it is a framework for meal timing – not a specific diet.
How does intermittent fasting work?
When you eat, your body uses energy from the food you consume and stores some of the excess for later. During a fasting period, once that readily available energy starts to run low, your body gradually draws on stored glycogen – a form of carbohydrate stored mainly in the liver and muscles – before relying more heavily on stored fat for fuel2.
Behind the scenes, your mitochondria help convert these fuel sources into usable energy for your cells, muscles, and everyday activity.
That change in energy use is one reason intermittent fasting is often associated with fat loss. However, fasting itself isn’t necessarily a shortcut to losing weight. For many people, one of its main effects is simply reducing the number of hours available for eating, which – alongside other sustainable food management strategies, such as meal prepping for the week – can make it easier to consume fewer calories overall.
Current evidence suggests that when intermittent fasting leads to weight loss, the biggest driver is still maintaining a calorie deficit over time. In other words, while intermittent fasting can be useful for some people, the fundamentals of a balanced plate – paired with regular exercise, such as F45 workouts – are still key to the overall picture.
Types of intermittent fasting
There’s no single way to practice intermittent fasting.
Instead, the term covers several approaches that vary according to how long you fast and how frequently those fasting periods occur. Some simply extend the natural overnight fast, while others involve more significant changes to your usual eating schedule.
Here are three of the most common types of intermittent fasting.
Time-restricted eating (TRE)
Time-restricted eating is one of the most common approaches to intermittent fasting. It involves fitting your meals and snacks within a set daily eating window, then fasting for the remaining hours.
You may have come across schedules such as 12:12, 14:10 or 16:8:
- The first number refers to the fasting window
- The second represents the hours available for eating
A 14:10 approach, for example, means fasting for 14 hours and eating within a 10-hour window each day.
The timings themselves aren’t magic numbers. Different schedules may suit different lifestyles, routines and training demands, which is why finding an approach you can realistically maintain is more important than chasing the longest possible fast.
The 5:2 method
The 5:2 method takes a weekly – rather than a daily – approach. Typically, it involves eating as usual on five days of the week and substantially reducing your energy intake on two non-consecutive days.
Because those lower-intake days can have a bigger impact on energy levels and hunger, the 5:2 method can feel quite different from simply extending your overnight fasting window.
Alternate-day fasting
As the name suggests, alternate-day fasting involves alternating between regular eating days and fasting or significantly reduced-calorie days.
It’s one of the more restrictive forms of intermittent fasting and can be more challenging to maintain over the long term. As with any eating pattern, sustainability is crucial – and an approach only has value if it works alongside your broader nutrition and lifestyle needs.
Intermittent fasting: 3 benefits
Intermittent fasting can offer several potential benefits – although how well it works will depend on the individual, the fasting approach, and other lifestyle variables.
1. It may support weight management
For some people, having a defined eating window can make it easier to manage their overall calorie intake. With fewer hours available for eating, you may naturally reduce how much you consume across the day. That said, intermittent fasting doesn’t appear to produce dramatically different weight-loss results from other sustainable, calorie-controlled eating approaches3. The most effective strategy is ultimately one you can maintain over time.
2. It may support metabolic health
Some research suggests that intermittent fasting may improve certain markers of metabolic health in some people, including measures related to blood sugar regulation and insulin sensitivity4. However, these effects can vary considerably between individuals (which is just one of the reasons why it’s so crucial to understand your unique biology) and intermittent fasting shouldn’t be viewed as a guaranteed way to improve metabolic health. Your overall diet quality, activity levels, sleep, and other lifestyle habits still all play a major role.
3. It can provide a simple eating structure
One of the most practical benefits of intermittent fasting is its simplicity. Rather than tracking every meal or excluding particular foods, you’re primarily working within a set eating window.
For some people, that structure can make healthy eating feel easier to organize around work, training, and everyday life.
Common myths about intermittent fasting
Intermittent fasting has attracted plenty of attention – and, with it, plenty of misconceptions.
Here are three common myths worth clearing up.
“Fasting burns more fat than other diets”
Because your body relies more heavily on stored fat during a fasting period, it can be tempting to assume that fasting automatically leads to greater fat loss.
In reality, your holistic long-term weight loss management plan will still be driven largely by your overall energy balance. Intermittent fasting can help some people create a calorie deficit, but it doesn’t necessarily burn more body fat than another eating pattern that results in a similar overall calorie intake.
“You can’t build muscle while intermittent fasting”
Building and maintaining muscle is less about exactly when you eat and more about consistently giving your body what it needs to adapt.
Resistance and hybrid workouts at F45 Training are ideal for building muscle. Utilizing the principles of progressive overload – gradually increasing the weight, reps, tempo, or volume of your exercises – they’re built to develop your muscle endurance and strength.
That said, it’s vital to ensure you’re pairing the benefits of strength training with sufficient protein (plus enough overall energy from your diet) to support muscle growth. That means intermittent fasting and strength training can coexist – provided your eating window still allows you to fuel your workouts and meet your body’s nutritional needs.
“Everyone should skip breakfast”
Skipping breakfast is sometimes treated as synonymous with intermittent fasting, but it certainly isn’t a requirement. A fasting window can be structured in different ways: some people feel better eating earlier in the day, while others prefer a later first meal.
Can you exercise while intermittent fasting?
Yes – intermittent fasting can be combined with regular exercise, and research in adults suggests that time-restricted eating doesn’t necessarily compromise physical performance5.
But whether you prefer to train during a fasting window or after eating can come down to the type of workout you’re doing, how your body responds, and when you feel most energized.
Cardio training
Some people enjoy doing cardio before their first meal of the day, while others find they have more energy after eating. (If this is you, don’t sleep on our guide to what to eat before a workout!) There’s no need to force a fasted workout if it leaves you feeling flat or makes it harder to perform at your best – it’s all about listening to your body.
Resistance training
Intermittent fasting doesn’t necessarily rule out strength training, but your eating window still needs to give you enough opportunity to fuel your sessions and support proper post-workout recovery. If you find that fasting leaves you struggling to complete your workouts or meet your nutritional needs, try adjusting your fasting window instead of simply pushing through.
Recovery
Rest days and recovery are just as important as the workout itself. Your body needs enough energy, protein, fluids, and other nutrients to repair and adapt after training – alongside quality sleep and all seven types of rest.
If you choose to combine intermittent fasting with an active routine, pay attention to how you feel between sessions (not just during them!) and be sure to book a recovery workout at your local F45 studio to rest, recharge, and reinvigorate your mind and body.
*This article is not intended to serve as medical advice
Now that we’ve unpacked what intermittent fasting is, continue this nutritional deep dive with our guide to foods that help you sleep – or unpack the science behind sugar addiction.
2 https://www.nia.nih.gov/news/research-intermittent-fasting-shows-health-benefits
3 https://www.bmj.com/content/389/bmj-2024-082007
4 https://dom-pubs.onlinelibrary.wiley.com/doi/full/10.1111/dom.16092
