Just like filling up a car, our bodies need fuel to perform. And the type of fuel matters too – clearly an unleaded car won't function on diesel.
Olympian Jessica Hull runs about 130 kilometres every week. When you break that down, it is 18 to 20 kilometres each day.
So, what Hull eats needs staying power.
"Fuelling is as important as doing stretches when you finish running, or doing core work in the gym," Hull said.
"Especially at this level, you can't get away with not taking care of those 1 percenters."
The 26-year-old distance runner holds the Australian record for the 1,500 metres, the mile, 3,000 metres and 5,000 metres.
She has been on the professional scene for three years now and credits those records with covering all bases, on and off the track.
Sally Walker was the Australian team's dietician for the 2021 Olympics and 2022 Commonwealth Games.
She has extensive experience working with athletes at the New South Wales Institute of Sport (NSWIS) and is now the president of Sports Dieticians Australia.
Walker said when using food for performance, there are several factors to consider.
"What we really need to look at first is what are the athletes' physiological needs and what energy systems are they using?" she told ABC Sport.
"If it's a long-distance runner who's got sprinted intervals or a weightlifter that might need to get stronger and gain muscle mass – all these things will change what that person should eat."
So, what does a runner need?
Hull changes up her menu each day because she likes to cook. But she knows carbohydrates and fats need to be her staples, and her body knows it too.
"I'll definitely honour it if I have a craving, but I tend to find when I'm training really hard, my body craves that correct fuel," Hull said.
A typical day consists of food like yoghurt, muesli, a banana, toast, peanut butter, eggs, avocado, rice, vegetables and either fish, chicken or steak.
"I think if you're under-fuelling and you're in a calorie deficit, you're going to crave calorie-dense foods, and that's usually the unhealthier ones," Hull said.
"But I think if you're keeping things balanced, and making sure you're getting enough in, it eliminates that."
Carbohydrates, proteins, fats
Energy comes from foods and fluids containing carbohydrates, proteins and fats. Once they're broken down and absorbed into the bloodstream, they get to work fuelling the aerobic or anaerobic energy systems.
When the body needs to get up and go, that ignition comes from creatine (a substance stored in our muscles, primarily from foods like meat and fish), which engages blood sugar levels for easy access to glucose from the carbohydrates you ate in your last meal.
If blood sugar levels start to drop and you need to keep going, the body will use glucose from glycogen, which is effectively stored carbohydrates in the muscles and liver.
"In this peak level of output, carbohydrates are the primary and most efficient fuel source for the body to use anaerobically," Walker said.
When it comes to distance running, the reduced intensity allows for a greater oxygen flow, so the aerobic system comes into play.
"However, there's only a limited store of glycogen and carbohydrates in the body, and if you aren't well fuelled, performance can drop off sooner than you might like," Walker said.
Full glycogen stores will last around 60-90 minutes, then things will start to slow down if there isn't another carb top-up during the activity (this is why marathon runners will often be seen sucking down gels during a race).
With oxygen present though, the body can utilise fats as a fuel source.
"To train aerobically at a lower intensity and allow fats to be used as a fuel source, the athlete needs a good oxygen capacity in training to maintain performance to not feel heavy in the legs, get the wobbles or light-headed and hit the proverbial wall," Walker said.
"If there aren't enough carbs present for these higher intensities it's likely either performance will drop off or the body will have to break down protein to fuel activity, which may impact overall strength in the long term."
And for those requiring less stamina?
If you're not going the distance – literally — you will largely be using your anaerobic energy system, like Olympic weightlifter Kiana Elliott. She competes in the 59-64-kilogram division.
The 25-year-old trains in the gym for three to four hours a day.
"Weightlifting is made up of two movements, the snatch and the clean and jerk. And the training is both exact movements, or variations of them," Elliott said.
Training and nutrition here is a tricky balance. An athlete needs energy but does not want to be breaking down muscle or have an excess to fall out of the weight category.
Because they are not relying on an oxygen flow like a runner, fats are not used as efficiently. Carbohydrates are primarily needed to sustain strength sessions, and protein and even more carbohydrates to build up and repair muscle.
"A weightlifter, who does more peak power, short-burst activity, will again be using carbohydrates," Walker said.
"They're likely to break down their muscle mass and protein stores more if there's no carbohydrates present."
As an athlete in a weight-category sport, Elliott weighs herself and her food each day to track her progress.
Dinner is often a piece of protein (meat, chicken or fish) that weighs up to 150 grams, a 130-gram portion of rice or carbohydrate and about one cup of vegetables.
Lunch is usually a wrap with lean meat, eggs (from the backyard chooks) and vegetables. Sometimes she throws a bit of cheese in.
But she won't deny herself a treat if she's craving it.
"My favourite food is chocolate, and I do have some every day pretty much," Elliott said.
"Fats are probably the easiest to reduce because they have a minimal effect on your training, but there's always a minimum amount you want to get in because it's really important for your hormone health, especially as a woman."
A genuine balancing act
As we know, everyone is different, and Walker says it is essential to listen to your body.
"It's telling them things for a reason," she said.
"Paying attention to when you are tired, hungry, injured or frequently getting cold and flu it might be signs your diet isn't aligning with your body's demands and it may not only be impacting your performance, but your overall health.
"[For women] menstrual cycles are a really valuable part of this – if individuals have skipped a cycle because they're not fuelling enough, that's a message from the body.
"Other messages from the body might be if you're not urinating very often, you might be dehydrated. Stool consistency might be an indication of gut issues.
"So, man or woman, it's listening to 'what's the body trying to tell me now and should I be trying to find some answers to what's actually happening, to then change my diet to suit that?'."
Discussing these issues with an accredited sports dietician is a great place to start solving these problems.
Lastly, timing can make a huge difference
Although there is crossover with what foods different athletes eat, the application to their training schedule and ultimate goal is where science can play a big part.
"When they should eat, what they should eat and the frequency of it … that's when we can be really specific and use food to a performance advantage," Walker said.
"They don't give out gold medals for who has the best diet, they give it for performance, so we really need to engage with that."
Walker said the biggest way to manipulate the diet is through the timing, frequency and portion sizes of meals.
"The individualisation comes with when they're eating it specific to their training times and how frequently they're eating after that, to be able to meet their needs to either recover from training or to prepare for the next training session," she said.
Hull regularly runs 12 kilometres in the morning and six in the afternoon.
About three hours after breakfast and straight after her first run, she will have a protein shake.
If she is going to the gym straight afterwards, she will pair that with a carb, but if not it is lunch right away.
Before Hull's afternoon session, she will have another snack and then, of course, dinner after the run.
For all of us, elite athlete or amateur, the following advice could make all the difference.
"Rather than think 'I should eat this and it's the right food to eat but I hate it' — it's going to be a terrible experience for you," Walker said.
"If you can eat and say 'this is going to get me to where I need to be', it becomes a choice, rather than an obligation."
