How eating more might improve your exercise performance

Following a good diet and taking regular exercise have long been touted as essential for good health, but how do you know if your diet is helping or hindering your exercise routine?

The spotlight is on long distance running with marathon season having arrived. The London Marathon has already taken place and May will see plenty more take place throughout the UK with participants running, jogging and walking the 26.2 miles. But how should they fuel the mammoth physical challenge?

Endurance athlete and doctor Elsey Davis, has learnt a lot about this over the last nine years, with a few mistakes along the way. Working with sports dietitian, Renee McGregor she has now found the best approach for her. McGregor and Davis share their experiences and expertise…

Under-fuelling can lead to injury and serious medical problems

Under-fuelling is when your total energy intake isn’t enough to meet your needs and perform your best. McGregor says it most commonly refers to not having enough carbohydrates – the nutrient that’s regarded as ‘fuel for fitness’.

Despite following a ‘healthy’ diet and making sure she didn’t cut out any major nutrients, Davis was a victim of this.

While Davis was eating normal, everyday meals, fitting in intense early morning training around long hospital shifts made it hard to prioritise the extra nutrients and energy she needed. Sporadic breaks also made it hard to know when her next snack or meal might be.

“I’d be tired from rushing around and quite often train before breakfast… It wouldn't be clear when I’d get a break when working on the [hospital] ward or if I'd even get to have a break.”

This led to Davis suffering with recurrent stress fractures, tiredness and a decrease in her performance. She was then diagnosed with the serious medical condition RED-S (Relative Energy Deficiency in sport).

“RED-S is when there’s not enough energy to support all movement and biological processes, says McGregor, before adding: “It’s further impacted by internal stress on the body. Stress can be not fuelling enough, losing weight rapidly, training at too high intensity with little or poor recovery” explains McGregor.

It can also lead to other health issues: “It can impact your red blood cell production, so often we will see low iron levels in individuals who are in RED-S,” says McGregor.

Under-fuelling can also affect hormone levels. “Under-fuelling can lead to disruptions in female hormones which can lead to irregular or even loss of periods. If you don't have regular menstrual cycles, this starts to have a negative impact on other areas of your health and can lead to injuries such as stress fractures.”

Davis describes how losing your period was historically considered the norm in elite athletes, “it used to be seen that if you lost your period, it meant you’re training hard. Now, we know, losing your period is a key sign of under-fuelling. It's a sign you need to pull back and your body is under stress.”

It’s not just professional athletes who are at risk of under-fuelling

McGregor has seen under-fuelling, which underpins RED-S, in all types of individuals, from everyday gym users to personal trainers, football players, swimmers, ballet dancers and even those that have followed faddy and very restrictive diets. Females are more vulnerable to it (primarily due to the body’s requirement to protect reproductive functions).

“Some people think that if you're eating regular meals that should be enough to carry you through. The reality is, if you're training every day, you're constantly using up your glycogen stores.”

Glycogen is the body’s stored form of glucose – which is our main source of energy and comes from carbohydrates in food such as potatoes, rice, or bread as well as in fruits and juices. And it’s not just needed for exercise.

Everything from nerve and brain function to adrenaline (crucial on race day) is reliant on us having enough glucose.

Early signs of under-fuelling

Davis explains how her under-fuelling snuck up on her, “It's subtle and you might just put it down to tiredness from training. You need to know what's normal tiredness and when you're pushing too hard.”

Early signs of under-fuelling include:

• Lethargy and aches
• Lack of progression in training
• Sleep disturbance
• Low mood and irritability
• For women, if there is a change in menstrual cycle that is out of the ordinary. For example, if periods become further apart, shorter, closer together, lighter or stop all together

While Davis didn’t lose her periods, she showed other symptoms of RED-S and blood tests also showed her hormones were impacted.

Prioritising fuelling makes a difference

So, what did Davis do to combat this? In a video posted to her social media, Davis describes how gaining 3kg improved both her health and athletic performance. It lowered her heart rate, her sleep quality was better and her fitness and general motivation to train improved.

“I made simple changes and fully focused on fuelling,” states Davis. The changes Davis made were:

• No longer being complacent with preparing meals. She organised her time so fuelling became a priority
• Re-fuelling after running with a protein shake or chocolate milk within 20 minutes of exercise. This was to replenish glycogen stores and provide protein for muscle repair
• Ensured her diet was balanced, including all major food groups
• No longer relied on hunger cues, because excessive exercise can supress the hormone that makes you feel hungry
• Increased meal portion sizes and added extra carbohydrates as part of pre and post running snacks

The result of making these changes? “I noticed positive benefits of fuelling more within weeks… despite training less and gaining weight I have noticed my fitness has flown up and I’m in a much better place mentally and have much more motivation to train.”

How to tell if you are under-fuelling

“If you find yourself being chronically fatigued, low in motivation, have recurrent niggles and maybe even coughs and colds, these can all point towards poor fuelling,” says McGregor.

If you have experienced symptoms and are trying to increase your energy intake, McGregor says the most obvious sign it’s working is if you see progression both in performance and body composition.

“You’ll have enough energy to train and recover well between training sessions and be motivated to train.

As for Davis, the signs her dietary changes have worked are clear, “I used to get recurrent stress fractures, which I believe was a combination of overtraining [something Davis has also addressed] and under-fuelling. Changing my dietary habits have contributed to less sport-related injury.”

If you are experiencing any of the symptoms above, McGregor encourages people to seek help from a health professional.

If you have been affected by disordered eating, help and support is available

Originally published April 2024