WHEN Melbourne co-captain Jack Viney decided to shed weight to address a history of painful stress fractures, he recalled a conversation with rugby league superstar Cooper Cronk.

"I sat down with him to pick his brains," Viney said on a recent episode of Damian Barrett's In the Game podcast. "He said he liked to experiment in the off-season with what worked and what didn't."

Cronk's try-it-and-see approach led Viney, 25, to trial intermittent fasting.

During Melbourne's 2019 pre-season he cut out breakfast and late-night snacks, eating only between noon and 8pm. You can listen to his conversation with Barrett below (the fasting discussion begins at 09:13).

Find In the Game on Apple Podcasts, Google Podcasts and Spotify.

How have footballers' diets changed?

Growing up, Viney said, the received footy wisdom was to "smash carbohydrates".

"You're told what's best. When I was a 17-18-year-old I was told, 'You've got to smash carbohydrates for performance'.

"I was eating pancakes before breakfast, then breakfast with orange juice. Then at lunch I'm smashing carbohydrates. Get to dinner, loading up on pasta, then before I head to bed I'm having pancakes again.

"All this effort to carbohydrate load, and I got to game day and I felt terrible. Heavy, slow, lethargic."

What is intermittent fasting?

As he set out to prevent recurrences of the foot injury that cost him 15 games in 2018, Viney initially tried the 5:2 program, where he would eat normally for five days per week and drastically reduce his calorie intake for the other two days.

"I didn't last long at all," he said.

"Trying to train with nothing in your system for a couple of days, I felt like garbage. I gave that up pretty quickly."

Viney's approach, the 16:8 diet, is also known as time-restricted feeding. Participants fast for a 16-hour block in a day and 'feast' during the remaining eight hours.

"It was hard to begin with," he said. "You can have water and black coffee. You go through an hour or so feeling you want to eat. But you push through that and get to midday and start eating.

"I thought it was manageable. I felt great, the energy was good. It really worked for me and I'm sticking with it."

Viney fasted in 16-hour blocks, eating only between 12-8pm. Picture: AFL Photos

What does the science say?

Lisa Middleton is a sports dietitian who has worked for three AFL clubs – Essendon, Hawthorn and St Kilda – along with elite clubs in rugby league, soccer, netball and basketball.

Reducing weight by limiting food intake, she says, is intermittent fasting's most obvious effect.

"It's not that there's anything necessarily magical about intermittent fasting, but for a lot of people it adds some structure to their day and they only eat during that short, eight-hour period.

"A lot of people feel good doing it. Whether it's the fact it stops them from over-eating, or that when they're on some sort of diet and they have a goal, they consciously tend to eat less and make better food choices."

The science on further benefits is not settled, with studies on humans still relatively thin on the ground.

"There are some human studies that show benefits like weight loss, increasing metabolism, and for some diseases like diabetes because it may affect insulin levels, and there's also the whole anti-ageing thing," Middleton said.

"It will be interesting to see where the research goes in the future in terms of potential benefits other than weight loss. It's been a bit of a fad over the last few years and if more research is done and it shows more benefits, it would gain more merit and probably become more mainstream."

Some research suggests it would be better for those following the 16:8 routine to start eating earlier – from 8am to 4pm, for example – because of the positive effect it would have on some hormones and, importantly, it would also reduce food intake at night.

'I felt great, the energy was good,' Viney said of the approach. Picture: AFL Photos

How suitable is it for elite athletes?

The general view among dietitians is that if athletes are determined to fast, they are best advised to confine it to the off-season and perhaps only the early stages of the pre-season.

Middleton advises caution for athletes required to train at high intensity on a daily basis, and at different times of the day.

As high-performance machines, she said, they require regular food to fuel and refuel their tanks.

"I can't comment specifically on Jack Viney's situation, but intermittent fasting wouldn't be my first choice for athletes who are wanting to lose weight. You can still do that and be fit, healthy and lean without having to fast," Middleton said.

"If they're training in the morning and they haven't eaten since 8pm the previous night, my concern would be whether they've got enough fuel in their system to train.

"In pre-season, if their goal is body-fat loss it's actually often good to train before you eat in the morning, but if you're in-season and your body is trying to recover, that's where I'd be questioning how useful it is."

Intermittent fasting is generally not recommended for elite athletes during a season. Picture: AFL Photos

However, there are no hard-and-fast rules.

"Everyone's different. Different individuals respond differently to different ways of eating, and different athletes eat in different ways at different times of the season depending on what's going to work best for their performance," Middleton said.

"That's why it's important for club dietitians to individualise nutrition for each player.

"On game day, for instance, the mental combination of excitement and nerves or anxiety can affect your gut and mightn't allow you to eat as much as you would like. But other athletes can eat a meal an hour-and-a-half before a game and be totally fine. Everyone's different."

Lisa Middleton's three tips for intermittent fasting

Don't overdo the feasting

You've just survived 16 hours without food and the clock ticks over to 12pm. It's feasting time!

But Middleton says it's important to eat in moderation.

"Fasting programs don't work well for a lot of people because they overdo it during their eating window, or they don't make the best food choices," Middleton said.

"If you're doing that, most likely you're not going to see any benefits."

It's not for everyone

Before you padlock the fridge, you might want to consider whether you are a good candidate for fasting. Many people aren't, including skinny folks, youngsters and those coping with other health issues.

"If you're a light-framed person with a high metabolism, fasting is not a good idea because you may then have issues with energy levels, concentration and so on," Middleton said.

"There are some potential side-effects too. For example, fasting can cause constipation and gut issues.

"Pregnant and breastfeeding women should avoid it completely, along with anyone with a history of disordered or restrictive eating patterns."

Athletes trying to gain muscle won't achieve their goals if they fast, said Middleton, and "it's definitely not for people who are still growing and physically developing".

Eat well, not just rarely

"Before you consider changing your diet or adopting a new strategy, think about your general day-to-day nutrition. If you're not eating very well, try making healthier choices and see what results flow from that, rather than going straight to fasting.

"And if you've tried all that and you're still thinking about trying it, don't just go off and do it – consult a dietitian first."