Nutrition expert who has worked with Arnold Schwarzenegger and LeBron James eats a sugary kids' cereal for breakfast — and says you should too

• Depriving yourself of treats is a major reason why diets fail, according to a top nutrition advisor.
• Avoid the cycle of restriction and guilt by making space to eat things you actually enjoy.

If you want to lose weight and get healthier, ease up on your diet rules, according to a nutrition writer who's worked with stars like Arnold Schwarzenegger and LeBron James.

Adam Bornstein is a former fitness editor for Men's Health, best-selling nutrition and health writer, and editor-in-chief of Schwarzenegger's email newsletter. He says being too strict while trying to lose weight or get healthier can backfire, causing frustration and guilt instead of results.

In his new book, "You Can't Screw This Up," he offers tips on how to find an eating plan and exercise routine you can stick to — for life. Many diet plans fail because they prompt people to make extreme lifestyle changes, and then they feel guilty when they inevitably can't live up to the unrealistic expectations, according to Bornstein.

"You wouldn't throw someone in the deep end before they learn to tread water. We give people complex, difficult things to do and act surprised when they drown," he told Insider.

The advice in his latest book is distilled from more than nine years of research, including interviews with behavior change experts as well as his personal experiences struggling to find balance in a sea of health misinformation, he said in an interview.

"Start with what makes you happy, and then add the other healthy behaviors around that," Bornstein said. "That's the cheat code in life."

Your diet should include foods you love, especially treats

One of the biggest diet mistakes is assuming that all delicious foods have to be off-limits, according to Bornstein.

Whether it's cutting out carbs, slashing sugar from your diet, or swearing off take-out meals like pizza or burgers, people too often assume they need to be strict about their eating in order to get healthier or lose weight.

In fact, restriction can set you up for failure, Bornstein said.

He compares dieting to puling back a slingshot — every rule or banned food on a diet creates more and more tension, until something has to give. This slingshot effect can lead to yo-yo dieting, periods of restriction followed by bingeing and then even more restriction to compensate

To break the cycle, he says to stop trying to deprive yourself, and instead make space in your diet for foods you really enjoy, regardless of whether they might be deemed "unhealthy" by wellness gurus.

For Bornstein, this means indulging in a bowl of Frosted Flakes several times a week. Despite the fact that sugary cereal isn't particularly nutritious, he said eating it has had no ill effects on his health, and benefits his diet by making it easier for him to stick to other goals.

As a bonus, you might find that once you stop thinking about certain foods as forbidden, it's easier to enjoy them in moderation, he said.

"When you leave this cycle of thinking that you need to live in restriction, you find a lot of the things you used to crave, you don't crave anymore," Bornstein said.

Don't panic if you miss a workout or overeat for a day

Too often, people try to be "perfect" with their eating or exercise routine — and respond to any setbacks by doubling down on impossibly strict rules, or giving up entirely, Bornstein said.

For example, someone trying to diet might follow up a so-called "cheat meal" by starving themselves the next day, or by deciding to go all-in on binge eating junk food.

Instead, the solution is to stop letting a small mistake derail your whole plan, and instead get right back to your routine without trying to compensate, according to Bornstein.

"The screw-up isn't the problem. Bodies can tolerate imperfections, what we don't tolerate is the extremes," he said.

Aim for consistency, rather than perfection. In order to get lasting results from a healthy routine, it needs to be something you can see yourself doing, and enjoying, for years to come.

"Health should not be a prison that prevents you from living," Bornstein said.