For Sydney-based personal trainer Simon Margheritini there's no such thing as a good cheat day.
"It's definitely not something I would want to advertise", Margheritini told The Huffington Post Australia. "I've personally never seen them work."
Popular with some bodybuilders and gym-goers, a cheat day is the idea that if you stick to your diet and fitness regime for, say, 6 days, you get to eat and drink whatever you want on the seventh.
Cheat meals are usually highly calorific, and tasty, and include junk food favourites like cheeseburgers, pancakes, pepperoni pizza and chocolate bars.
So common is the idea that there are more than 1 million posts with the hashtag #cheatday on Instagram.
Those who back the concept say cheat days provide a mental break from diet and exercise and can also kick-start the body's metabolic processes if you're on a low-calorie regime, aiding fat burning and keeping your body from entering "starvation mode".
It's not only gym-junkies who swear by the practice, with celebrities like Jessica Biel, Sandra Bullock, Beyonce and even Dwayne "The Rock" Johnson said to use cheat days to help them stay on track.
But Margheritini said cheat days weren't a good idea, despite their perceived positives.
Their biggest problem, he said, was that they framed exercise in the minds of those trying to get fit as an "escape" from the rest of the week.
This mental effect was often compounded by people scheduling a cheat day for the weekend -- the easiest time of the week to go overboard on food and alcohol.
"Say you have your cheat day on Saturday then when Monday comes along you're not happy, you've overdone it and the exercise on the Monday turns into a drag," Margheritini said.
"All of a sudden you're looking at your health and fitness negatively instead of positively. That's a huge thing, and in that instance cheat days become a psychological barrier to making gains.
"From there, a cheat day can easily become 2 or 3 days and then you've lost focus."
Core Performance's Jade Pearman agreed. She said it was better to enjoy every day of the week instead of struggling with a diet and fitness program that promised 6 days of toil with a splurge on the seventh.
She said in her experience cheat days could be especially unhelpful for women, some of whom already had a complex relationship with food.
"For me a cheat day is rewarding yourself for doing something when really it should be a part of your lifestyle," Pearman told HuffPost Australia.
"You should enjoy everyday. People need to find that balance between having a healthy relationship with food and not feeling the need to have a cheat day once a week.
"There's so many dysfunctional relationships around food, especially with women, so I try to educate my clients to enjoy what they eat on a daily basis."
She advised people to "balance out" their calorie intake each day instead of incorporating a cheat day.
"I think it is ok if they do want to have that night where they're going out for dinner not to look at it as a cheat meal, try to be ok with it," Pearman said.
"Try to balance out the day and if you know you're going out for dinner try to prepare yourself and compensate for that earlier in the day."
Go and Get Fit's Margheritini said another problem with cheat days was they could descend into binge eating and drinking.
He said it was common for people to consume up to 4,000 calories on a cheat day compared to between 1,500 and 2,000 calories on a regular training day.
The average calorie intake for people between 31 and 50 who don't exercise is recommended at 1800 for women and 2400 for men, according to the Australian Healthy Food Guide.
Margheritini said, in his view, the only upside of cheat days was as a motivating tool for people kicking off an exercise plan.
"It can encourage people to start to exercise knowing that in the week there's one day when they can eat poorly ... That can help in the first 1 or 2 weeks of starting out exercising," he said.
For those keen to cheat on their fitness regime, Margheritini had one key piece of advice -- no fast food.
"You can eat so much of it without getting full," he said.