Nothing compares to the sweaty, endorphin-loaded feeling you get after HIIT. Whether it’s at a class or done at home, the intense cardio workouts are a favourite for the mental and physical benefits they pack into such a short period of time.

If you want to get the most from your session, however, you need to think about your pre-workout habits. Many of us opt for a roll-out of bed and onto the mat approach, and that might be fine for yoga or low-intensity movement, but a physically and mentally demanding session like HIIT requires a bit more prep – particularly when it comes to what you eat. 

HIIT requires huge amounts of energy to get through powerful moves as fast as you can. For that reason, giving your body fuel beforehand is the logical thing to do. Yet fasted training has gone mainstream for its supposed health benefits, ranging from improved metabolism to better endurance.

So is fasted HIIT the way to go? “There is actually very limited research to support any supposed benefits of fasted training,” says Lily Chapman, exercise nutritionist at P3RFORM. And it turns out that the science doesn’t back skipping pre-workout meals if you want to perform well at high intensities.

In a 2020 review of the literature published by the Journal Of Sports Medicine, researchers suggested that “athletes train at relatively low intensities (and not at high-intensity levels) when fasting to ensure that they recover adequately to optimise performances in competitive events”. 

There are a few reasons why food before intense training is important. As mentioned, the amount of energy needed to perform at huge intensities requires calories (and specifically carbs). But there’s also the fact that HIIT places great stress on the body. 

“HIIT can lead to an increase in your sympathetic nervous system along with elevated levels of cortisol in the bloodstream,” says Chapman. While this stress is what helps the body adapt to your training, too much of it can be a problem. “If recovery from these sessions is not optimal, especially around nutrition and sleep, this can lead to heightened symptoms of physical stress,” says Chapman.

Preparation is part of that recovery. Asking hugely demanding things from your body without the energy supply it needs only adds extra stress, meaning recovery is harder. Plus, for women, the huge cortisol spike can interrupt other hormones (particularly reproductive hormones like oestrogen). The long term impact of fasted HIIT can even be amenorrhea, which is the loss of your menstrual cycle. 

Chapman says that, for those who find they feel more alert and energised on an empty stomach and have otherwise sound nutrition, the odd fasted HIIT session may be OK. However, she stresses: “If you are someone who prefers food prior to training, have limited time or feels lightheaded if you don’t eat prior then eating is a good idea.”  

When it comes to getting the most from your HIIT, carbs are king. A Nutrition Today report from 2018 states that carbohydrates are most efficiently metabolised by the body and “the only macronutrient that can be broken down rapidly enough to provide energy during periods of high-intensity exercise when fast-twitch muscle fibres are primarily relied upon”.

“As HIIT is an intense training session a moderate amount of carbs would be ideal to provide the required energy when training. Low-carb diets can decrease physical performance, increase perceived workload and exertion and the ability for your body to recover optimally following training,” says Chapman.

The type of carb is also important. “Eating a high fat or fibre meal prior could cause gastrointestinal discomfort for some individuals,” Chapman explains, so choosing fast-acting carbohydrates like fruit, cereals or rice cakes is beneficial. “A bagel and jam, porridge oats and honey or a small bowl of tuna pasta can be good pre-workout snacks,” says Chapman. 

She also recommends between one and four grams of carbs per kilogram of body mass within the few hours before exercising. If you weigh 70kg, that’s 70-280g of carbs in your system to get you through the strain of HIIT – that’s around 70g of oats with a medium banana or a couple of slices of toast with jam. “Try to leave 30 minutes between eating and working out to avoid digestive issues,” she adds.

Having a source of protein can also be useful for recovery. “Though it’s not a food source that improves training, it is a key macro to support muscle function,” she says. Research by the International Society of Sports Nutrition shows that protein within a few hours of your workout is the most important for recovery – and it doesn’t matter if this is before or after the session, so it’s advised to get it first if you know you’re busy after, says Chapman.

The most important thing to remember is that HIIT is hard – and your body knows it. Giving it some fuel beforehand will probably help you jump and crunch faster while supporting your long-term health – and who would refuse health-benefitting bagels? 

Images: Getty