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Low energy: how to properly fuel your body to complement your exercise

Posted by for Wellbeing

Missing periods, mood swings and slow fitness progress? Here are the key signs you could be under-fuelling your workouts (and what you can do about it). 

Emily Solman was in her second year of university when her body started acting weird. “My appetite was really up and down, I felt so stressed and tired pretty much all the time,” she says. She was doing everything right, she thought: exercising regularly, eating ‘healthily’, studying for a degree she loved, enjoying time for her friends and fulfilling her job as an influencer. So why had her hair lost its curls, her mood hit an all-time low and her sex drive and period gone AWOL?

Concerned, Emily’s friends suggested that she might not be eating enough. She scoffed at the idea. “I was studying nutritional science, so I thought I was pretty clued up on what my body needed. I exercised first thing in the morning for stress management, I’d eat a large breakfast of porridge, take lunch into the library with me and snack on things throughout the day, then come home to a big dinner,” she says. Yet, she couldn’t shake the feeling that something was up. 

So she spoke to her doctor, mainly about her abnormal menstrual cycles, and eventually went to an expert who told her she was suffering with Relative Energy Deficiency in Sport (REDS). Most common in athletes (hence the ‘sport’ in the name), REDS is becoming increasingly common in the day-to-day gym goer. Yet, for those who live with the condition, low energy may not feel like the main issue. 

“I had never noticed any weight loss and I just didn’t understand how food could have been an issue for me,” Emily says. But it turns out, the relationship between exercise, diet and hormones is more complicated than many women think – and the impact is serious.  

What is energy deficiency?

“Energy deficiency is when there’s just not enough available energy to do the work that the body needs to do,” explains Renee McGregor, sports dietician from the Strong Women Collective and specialist in athlete health and energy deficiency. “The way in which I define ‘work’ is any training that you do, your general movement – walking up and down the stairs to make a tea or coffee – and also the biggest part that no one pays attention to: our biological functions.”

The body needs more energy than you might think to do these things, explains Renee. Except, we live in a world that emphasises ‘moving more and eating less’ as the key to health. Lockdown hasn’t helped. Right now, Renee’s clinic is busier than ever, receiving up to 60 referrals a month from women who are dealing with the symptoms of under-fuelling.  

A woman checking her exercises stats on her phone and watch.
Low energy availability: moving more and eating less isn't the answer.

“What I’m noticing is that everybody is really worried because they’re sitting more, rather than walking around catching trains and buses every day. They’re trying to overcompensate by doing more activity, without taking into account that the more exercise they do, the more food they need,” says Renee. “I think there’s a lot of fear about being ‘lazy’. That term is bandied around a lot and people think they need to do something every single day. I don’t know where that’s coming from, because it’s not government advice.”

In fact, she points out the fact that the government exercise advice for physical health is only 150 minutes in a week. And, if you look at the studies around mental health, the recommendations are around 30 to 40 minutes, three to four times a week.

“I am definitely noticing a push towards everyone doing more movement. But I’ve been in the sport and exercise industry for 20 years and never before have I seen so much identity around food. How you eat now seems to somehow suggest who you are. We’ve lost sight of the fact that actually what we look like and what we eat is a very small part of overall health,” says Renee.

How does REDS occur?

If you don’t skip meals, calories and energy aren’t a problem for you, right? That’s what Emily thought. “I thought that my relationship with food was pretty positive,” Emily says. “When I explained my diet to people I knew or posted What I Eat In A Day videos on my Instagram, everyone seemed to agree that I ate quite a lot.” 

“The problem is that people don’t realise quite how much fuel their body needs, because we rely on arbitrary numbers,” says Renee.  

“A fitness tracker could say that you’ve burnt X amount of energy, so the logic is that if you eat X amount of food, you will break even. But what if your body’s trying to make red blood cells? What if your body is trying to put down bone mass? What if you’re in a particular stage of your menstrual cycle when your requirements go up?” she asks.

“Those numbers don’t take into account the energy factors of stress, the fact that between 10-20% of the energy we eat is just used to digest our food, and let’s not forget the brain, which uses 20% of our energy requirements every day. Actually, the amount of fuel we need just to get through the day is actually quite a significant number. And then when you add movement onto that, it’s even more.”

But REDS isn’t just about energy in versus energy out. The types of food and the timings of our meals is more important than we’re ever taught about. 

“When we exercise, we’re stimulating all sorts of signals within our body. But those signals need certain nutrients to be able to deliver the goods,” she says. The main nutrient they require? Carbohydrates. “I’ve seen women who are normal weight and probably eating the right amount for their training, but they’re on keto or paleo diet, so they’re not delivering the carbohydrates that they need,” Renee says.

While Emily wasn’t ever intentionally cutting carbs, she trained without eating anything beforehand, meaning that her body wasn’t being given the glucose it needed to send the right signals around her body. 

“I trained first thing because it was the only time I could fit it in my busy day, and I always ate straight afterwards,” she says. It was only after seeking professional help that she realised her body was actually struggling through fasted training, and her post-workout meal of porridge and blueberries wasn’t serving up enough fuel.   

“There’s a lot of evidence that shows that your thyroid needs enough carbohydrates to release the T3 hormone. Without carbs, the hormone production can be blunted, which then impacts the hypothalamus – the main hormone centre in the brain,” Renee explains. Once the hypothalamus is out of whack, there are all sorts of knock-on effects to your body.  

How to spot energy deficiency

The most clear signal for a lot of women is a lack of, or change to, their periods. It’s due to that slow working hypothalamus dulling down the hormones, and the body’s primal desire to prioritise movement over internal function.

“You might notice that they get lighter, shorter, longer or stop altogether. Fundamentally, no period means that your body’s getting to the point where it’s shutting down biological function,” explains Renee. 

It’s why another symptom of energy deficiency is poor digestion, because “if there’s not enough energy in the system your body can not break down food. You might find that you get symptoms very similar to IBS, but it’s actually just slow movement of food through the gut which feels quite crippling and really painful. A lot of times people think they’ve got a food allergy or food intolerance, but the worst thing they can do is take more food out of their diet.” 

Other symptoms might include low mood, as oestrogen is responsible for the uptake of serotonin. Without it, you might experience feelings of depression, poor memory and brain fog. In terms of exercise, you might find that you’re not recovering properly in between sessions and experiencing an increase in muscle soreness. You might not be adapting to training, either – for example, you could have an expectation of strength gains over a certain period that your body just isn’t meeting.

“Another one of the key things about low energy availability is that your body will try to stay awake to ‘hunt’ for food, so your sleep can be quite significantly affected,” she adds. 

“All of these symptoms could also be related to the pandemic, but I do think it’s important to highlight them because they could be something more,” says Renee.  

How to properly fuel your training

How can you really know how much food your body needs? Clearly, there’s no one-size-fits-all prescription, but generally “most women shouldn’t be doing any form of fasted training,” says Renee. “This can be the starting point of low energy availability.” Forget what you think you know about fasted training burning more fat – it’s not true, says Renee. And it’s certainly no reason to put your hormones into disarray.

It doesn’t mean you have to eat a huge meal before you workout either, but trying to have a large banana, some toast or a few rice cakes before working out, particularly if you are a morning exerciser, will give your body the fuel it needs.

Then, it’s about paying attention to your carbohydrate intake throughout the day. That doesn’t mean counting your macros, but being aware of the importance of them. It’s hard, given the mainstream demonisation of the nutrient, but it’s crucial.  

An avocado sandwich on a plate.
Low energy availability: eating carbs is important, even on rest days.

“Getting into numbers is tricky, because everyone is different. But one thing that we do know is that no woman should eat less than 3g of carbohydrate per kilogramme of body weight. Ever. Even on a rest day. And on an exercise day, they probably need a lot more in order to regulate hormones and to help the body adapt,” says Renee. That means that if you’re a 70kg woman, you shouldn’t be having less than 210g of carbohydrates, even on the days that you don’t actively train. 

“Try not to be erratic with your eating,” says Renee. “Don’t leave gaps longer than four hours, because that’s when blood sugars will start to drop. Having regular eating times, and those times can be whenever suits you, will help avoid low energy. I also think that, right now, it helps with the stress, knowing you’re going to have a break in the working day.”

Aside from food, being careful about your exercise is important too. No matter what people say or show online, you don’t need to put your body, brain and hormones under the stress of ridiculously intense workouts. “Trying to move every day is not a bad thing, but nobody should be doing highly intense training every day. It’s OK if your movement is simply a walk or a yoga session – that’s enough,” says Renee. “And you never have to earn your food through exercise.”

Take it from Emily, who had to re-learn everything she thought she knew about exercise and eating to lead her to where she is now, fully recovered from REDS and more knowledgeable than ever about her exercise and nutrition. “My body was in survival mode, even though I looked fine from the outside,” she says. “No amount of aesthetically pleasing abs is more important than your body actually working, and my body did not work.”  

Images: Pexels / Getty

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Chloe Gray

Chloe Gray is the senior writer for's fitness brand Strong Women. When she's not writing or lifting weights, she's most likely found practicing handstands, sipping a gin and tonic or eating peanut butter straight out of the jar (not all at the same time).

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