Fasted workouts may help some people burn more fat during exercise, but they’re not right for everyone. Nutritionists and trainers explain when training before breakfast makes sense – and when eating first is the smarter choice

As someone who often follows an intermittent fasting (IF) eating routine, where I roughly start my food intake around 12.30pm, I’ve lost count of the times I overthink when I exercise on no food.

From will I faint to do I have enough energy – I tend to do a bodyscan of myself to ensure I’m fully fit enough to either play padel or go for a 5k run without any food lining my stomach. And I’m sure I’m not the only one as for years we have been told to fuel up properly before working out to ensure better performance, energy, and muscle gain.

As with everything when it comes to exercise, there’s no one-size-fits-all answer. There’s lots of factors to be taken into account such as pre-existing health and lifestyle conditions, as well as what type and intensity of exercise you are doing. Also, it depends on what your “fasting” time is. For example, for those that follow an IF eating regime, it usually refers to a predominantly calorie free stretch within a 24-hour period.

“Definitions matter when we talk about restricting food and drink,” explained Dr Bruce Dorr, senior medical advisor at the HRT specialised practice www.biote.com

“The most common IF approach is when a person fasts for 16 hours, limiting themselves to water, sparkling water, and non-caloric caffeinated beverages, and then follows this with an eight-hour eating window.

“Exercising in the fasted state trains the body to move beyond its immediate energy sources, food and liver glycogen, and burn fat instead. However, the body needs time to adjust to running on that alternative fuel. It’s better to allow your body to adapt to the fasting itself before adding the stress of exercise on top of it.

“Exercising when missing breakfast is safe, but headaches and low blood sugar are real possibilities, so hydration becomes even more important. Keep fasted workouts under an hour and at low intensity.”

To understand exactly how the body behaves – and benefits – if exercising on no food, Annie Davies a clinical nutritionist at https://www.mybodyfabulous.co.uk/clinical-team helps to break it down.

“There are many potential benefits to exercising in a fasted state. For example, if someone exercises in the morning after an overnight fast and doesn’t eat until 1pm they may experience:

“Greater fat utilisation during the workout. With lower insulin levels and reduced glycogen stores, the body tends to rely more on fat as a fuel source, particularly during low- to moderate-intensity exercise.

“Convenience. Some people prefer training before work and don’t feel hungry first thing in the morning.

“Potential improvements in metabolic flexibility. Some studies suggest that fasted training may help the body become more efficient at switching between carbohydrate and fat for fuel.”

Get the knowledge

While exercising on an empty stomach isn’t inherently dangerous for most healthy people, it’s important to arm yourself with the knowledge of the possible disadvantages to consider as training without eating is not ideal or safe for everyone.

According to Annie, some of these include:

Reduced performance during high-intensity exercise – many may find that enjoy exercising when they fuel their body

• Lower energy and increased perceived effort.

• Dizziness or light-headedness, especially if dehydrated.

• Slower recovery if many hours pass before eating.

• Increased muscle protein breakdown if fasting is prolonged and protein intake over the day is inadequate.

“For women in particular, some people notice increased fatigue, changes in menstrual cycles if energy intake becomes chronically too low, elevated stress or poor sleep and difficulty recovering from frequent intense workouts,” she adds.

In fact, it is the recovery aspect of training on an empty stomach that personal trainer Edwina Jenner, who specialises in strength training for women over 40 at www.edwinajenner.com is concerned about.

“For women in their forties and fifties often dealing with a heavy stress load in terms of disrupted sleep, the external pressures that come with this stage of life and hormonal changes, recovery is even harder.

“Training when fasted can increase fat use during that training session, but ultimately it’s going to come down to your individual energy intake, consistency, protein, strength training and recovery.

“From a personal perspective, very few of my clients train in a fasted state and many of them have come to me and said, “I used to do intermittent fasting but it wasn’t sustainable.”

“Having a little bit of fuel in your system before you start training can really be much more beneficial than training in a completely fasted state. Some women I work with like to have something small before they train, and other women prefer to fuel more and train a little bit later.”

What type of exercise works best?

Exercise type is an important consideration. Some people may find that walking, yoga, mobility work, light strength training or an easy run may be well tolerated. Whereas longer runs, HIIT, heavy resistance train or competitive events would likely benefit from eating beforehand to help improve performance and indeed enjoyment.

According to Marshall Weber, founder of https://www.functionalidaho.com/ if someone is going for a walk, doing mobility work, or completing a moderate strength workout, exercising before breakfast is often fine if they’re well hydrated and paying attention to how they feel.

“I’d be more cautious with longer runs, high-intensity workouts, or heavy lifting. Those sessions place greater demands on the body, and many people perform better when they’ve had some fuel beforehand.

“One thing I encourage clients to look at is how they feel after the workout, not just during it. You can get through a session and still find yourself dragging for the rest of the day. If your workouts feel harder than they used to, or you’re taking longer to recover, it’s worth asking whether your nutrition is supporting the amount of exercise you’re doing.

“For women over 50, maintaining muscle becomes even more important. That’s why I always come back to making sure they’re eating enough protein and enough food overall. If an eating schedule makes it difficult to recover well or meet those nutritional needs, I’d rather adjust the schedule than ask the body to keep doing more with less.

In agreement is Nikkii Behrens, founder of https://rarepilates.com/en who also points to lower-intensity activities such as walking, light jogging, Pilates or mobility work for those wanting to work out before eating.

“There is little evidence that exercising fasted leads to significantly greater fat loss compared with eating beforehand when total calorie intake is the same,” she explained.

“If someone follows a 1 p.m.–9 p.m. eating window and misses breakfast, I’d recommend saving more demanding sessions, such as heavy strength training, HIIT or long runs, for later in the day after eating. If they do train fasted, they should prioritise a balanced meal rich in protein and carbohydrates once their eating window opens to support recovery and muscle repair.

“Ultimately, the best routine is one that supports consistent exercise, adequate nutrition and recovery, rather than simply training on an empty stomach because of a fasting schedule.”