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.

"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.

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.

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.

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.

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.

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.