New research calls the wisdom of training on an empty stomach into question, but is fed state exercise really the answer?
For many, it’s down to logistics; if anyone’s finding the time to chow down a protein-rich meal before a 7am date with the squat rack, they have more hours in the day than we do.
For others, the idea of eating anything before the email inbox is in full, incessant flow is as a nauseating as burpees on a hangover. Meanwhile anyone who’s showing up for exercise with fat burn in mind can console themselves that nothing torches calories quite like a fasted work out. Or does it?
If new research is to be believed, forgoing that pre-training toast may not be the metabolic boon you think it is. A study earlier this year found that motivation and energy levels before exercise were lower when participants were in a fasted state, while those performing fasted workouts both performed worse and enjoyed workouts less than their fed peers.
It’s the latest study, but by no means the first, to debunk the idea that exercising on an empty stomach is superior; in fact researchers have been challenging this received wisdom for decades. So where should you land on the fasted/fed debate?
FAST AND THE CURIOUS
Before you pick a side, let’s be clear on the meaning. ‘Being “fed” refers to the metabolic state after eating food, when the body is digesting and absorbing the nutrients,’ explains leading sports dietitian and Women’s Health Collective panellist, Renee McGregor.
She notes that this state typically lasts for up to four hours after eating, although it could last up to six, depending on the speed of your metabolism and what you’ve eaten that day; high-fat or fibrous food, such as whole grains, red meat and seeds take longer to digest than simple carbohydrates.
As such, when you wake up in the morning after an (ideally) eight-hour slumber, you’re probably in the opposite state: fasted. ‘What you eat the night before will always influence your energy the following day, but it won’t be available as direct fuel because your body will have broken it down and used it for energy,’ adds McGregor, dispelling the belief that a bowl of pasta at 7pm will have ‘carb loaded’ you for the morning.
It’s not just a dawn chorus scenario either; eating your first meal at 12pm and hitting the gym at 6pm will also land you in a fasted state.
Until now, most people found themselves firmly on one side of the fence, falling into Team Fasted if they wanted to burn fat, and Team Fed if they wanted to crank up their training, thanks to the performance benefits of the extra fuel.
‘When you work out in the fed state, your body uses the calories consumed as a form of energy,’ says sports dietitian Jenaed Brodell, founder of the nutrition consultancy company Nutrition and Co. ‘That can maximise performance, helping you work harder and for longer, while also repairing muscle damage post-workout.’
Being in a ‘fed state’ fuels your brain and nervous system, too, adds McGregor. Not only will you feel more alert, you’ll make faster, better decisions, giving you a vital edge, if you’re an athlete.
FULL BOON
So far, so Team Fed. But here’s where it gets a bit murky: those headlines touting the myriad benefits of fasted state training aren’t completely misguided. There’s been plenty of research proving the positives associated with working out without having eaten, from an increase in VO2 max to a ramped-up metabolism.
A 2019 study from the University of Bath concluded that exercising before breakfast improves blood sugar control, while a 2020 paper published in the Nutrients journal found eating after strength training was more effective for reducing muscle protein breakdown than eating before the session.
The disclaimer? All of this research was conducted on men –as a galling 97% of sports science research is. Compare them to the tiny number of studies looking at the impact of feeding in women and the differences are significant.
Case in point: a study from the University of Surrey and St George’s University, which compared the performance of both men and women during a 30-minute treadmill run at 70% of their max speed.
The results showed that while male participants benefited from waiting until after the session to eat, women burned more fat both during the workout and at rest for the remainder of the day when they consumed food before exercise.
Adding more weight to the female fed state is hormonal health. Take the stress hormone cortisol – levels of which have been elevated of late thanks to a pandemic, a cost-of-living crisis and a revolving door at Downing Street to name a few cortisol spikers.
Indeed, more than half of women reported higher stress levels in 2022 than in 2021, according to a survey by professional services firm Deloitte. What’s more, McGregor explains, women are more sensitive to stress hormones as a result of our reproductive cycles. But fed-state training could be a key weapon in your anti-stress arsenal.
‘In the morning, your cortisol levels naturally spike. Layering that with something that causes a greater increase in stress hormones, like a high-intensity session, will make cortisol levels rise and stay high throughout the day,’ says McGregor.
In contrast, eat before and you can reduce that spike both during the session and throughout the day, with one small 2015 study finding that 400 calories of food before a treadmill run reduced circulating cortisol levels after training by 36% compared with when participants trained fasted.
‘It's a multifaceted subject,’ adds McGregor. ‘But we know that fuelling properly is a key factor that underpins how women’s cycles work.’
NUTRIENT CYCLING
Should you still need convincing that the workout fast is best left in the past, let’s talk about your periods. While a fasted workout, in isolation, is unlikely to affect them, train on an empty stomach on a regular basis and your cycle will begin to notice.
‘In women, a lack of carbohydrates is associated with a blunting of the production of thyroid hormone, T3,’ explains McGregor. ‘That, layered with the excess cortisol, signals to the hypothalamus – the hormone centre in the brain – that the body is in a state of stress, which leads to non-essential systems, like the reproductive system and therefore the menstrual cycle, to be downregulated.’
While period loss (amenorrhea) is an extreme outcome of excessive fasted training, it’s more common than you might expect and the implications for your health are serious. ‘[Amenorra] can reduce your bone density, impact cognitive function, impair balance, cause your athletic performance to deteriorate and reduce lean muscle mass gains,’ warns McGregor.
It isn’t just cortisol that’s affected, either. A study published in PLOS One found that fasting decreases the production of kisspeptin. ‘This is a neuropeptide responsible for sex hormones and endocrine and reproductive function,’ explains female physiology expert Dr Stacey Sims.
‘It also plays a significant role in maintaining healthy glucose levels, appetite regulation and body composition.’ It means a hit to kisspeptin will disrupt the release of oestrogen and progesterone – the two key female reproductive hormones.
‘Women have double the amount of kisspeptin in their brains than men, which explains why women have a greater sensitivity to changes in their energy balance,’ explains Dr Sims. ‘This energy balance is disrupted through fasted cardio, as your brain perceives a deficiency in nutrients.’
Add exercise into the equation and you’ll only exacerbate your hormonal imbalance, adds Sims. Clearly, it’s a vicious cycle, but here’s the irony. A disrupted metabolism from low thyroid and high cortisol is also associated with ‘your body also storing more belly fat and weight gain,’ says Sims, so if you’re working out fasted to burn fat, your efforts won’t be rewarded.
FED UP
We’ll take a punt and assume that, at this point, you’re a paid-up member to Team Fed. So how do you go about turbo-charging that gym routine?
While research shows that eating before exercise boosts endurance, especially over an hour, intensity matters more than style, says Brodell. ‘At low intensities, eating first is less important as your body usually has enough fat stores to fuel the activity. But by consuming the right pre-workout nutrition, you can maximise your performance while also repairing muscle damage post-workout.’
If the thought of doing egg burps on your Peloton is enough to make you turn green, we hear you. Eating too much can cause mid-workout sickness for the simple reason that, during exercise, your body moves blood flow away from your digestive system, in turn halting the movement of food through your gut, in order to get oxygenated blood to the muscles you’re using.
But adequately fuelling before your sessions doesn’t have to be nauseating. ‘At high intensities, your body's primary fuel source is carbohydrates, so it’s especially important to have a carb-rich food source before training,’ says Brodall, adding that simple foods like toast or a banana that can be turned into fuel fast are particularly useful.
Still can’t stomach a pre-sesh snack? Start small, says McGregor. ‘You can train your gut to be able to handle food in the morning and before exercise. The key is to start eating low amounts and gradually increase the portion size.’
McGregor recommends aiming for 0.5g-1g of carbohydrates per kilogram of body weight, eaten up to three hours or at least 30 minutes before working out. For a 70kg woman, that looks like 35-70g of carbs before a fast or long run, HIIT session or heavy strength day.
To avoid muscle breakdown, Sims recommends adding 15g of protein to your pre-workout snack too, with easy and low-fat protein sources being your best option – think yoghurt, protein powder or a glass of soya milk.
Still Team Fasted? You do you. There are no hard and fast rules about how and when to eat and train and your daily caloric intake, activity levels and stress will all influence how well you tolerate fasted training.
If you eat enough throughout the rest of the day to recover well, it’s all good, says McGregor, with this caveat. ‘Try not to do more than two fasted sessions a week to avoid layering day after day of high cortisol levels. Those sessions should also be less than an hour long and at a pace you talk through – a yoga session or light jog for example.’
Feeling stressed, dealing with fatigue or hormone dysregulation? You’re better off leaving fasted training at the door. And if you're planning an intense session first thing, a carb-rich snack with support both your workout and your hormonal health at large. As McGregor puts it: ‘a nourished body is a healthy body’.
If some PB&J rice cakes could be the difference between a stressed-out body and a happy state of mind, crunch away, we say.
FED STATE FEEDS
One to three hours before training:
‘These small meals contain a good serving of carbohydrates and protein while being low in fat and fibre so you’ll digest them at pace pre work out,’ says Brodell.
- Two rice cakes with cottage cheese
- Fruit smoothie with one banana, a handful of berries and 150g of yoghurt, milk or soya milk
- 40g of granola (with some sugar content for a pre-workout energy spike) served with 150ml of milk
Less than an hour before working out:
‘These snacks are easy to grab and go while delivering between 30-60g of simple carbohydrates for fast energy.’
- A milky coffee and a banana
- Two Medjool dates with a teaspoon of peanut butter
