Rebel Wilson reportedly used the Mayr Method to lose weight. Here's what to know about the diet and its effectiveness.

• Rebel Wilson's significant weight loss this year is reportedly due to the Mayr Method, a diet based on 100-year-old theories from an Austrian doctor.
• Some of the advice is helpful, like eating slowly, cutting back on sugar, and adding more veggies, according to dietitians.
• But it also includes some bogus claims. Experts say you don't have to cut out caffeine, dairy, or gluten to lose weight, you can't change your pH level with food, and it's find to eat raw foods after 4 p.m.

Actress Rebel Wilson has lost a significant amount of weight in recent months after declaring 2020 to be her "Year of Health" and working with a personal trainer on her fitness goals.

She's also reportedly following a new diet called the Mayr Method, according to People. The plan is based on the ideas of an Austrian physician, Dr. Franz Xaver Mayr, developed about a century ago. It's now the basis of treatment at Vivamayr, a chain of luxury wellness and medical spas beloved by celebrities.

Experts have mixed feelings about the diet.

"I've been a clinical dietitian for more than 20 years and I've never had anyone come to me and say they've been doing this," Sue Heikkinen, head registered dietitian for the calorie tracking app MyNetDiary, told Insider. "It's not one of the popular ones, and maybe for good reason."

While it includes some good advice, such as eating more slowly and cutting back on sugar, many of its claims aren't supported by evidence and could in fact stall weight loss efforts, according to dietitians. Here's what experts say about the diet's rules and whether you should follow its advice.

Rule: Eat mindfully, and chew eat bite 40 times

Does it work? Kind of.

Eliminating distractions and focusing more on the experience of eating can be a good thing, according to Bonnie Taub-Dix, registered dietitian nutritionist and author of Read It Before You Eat It - Taking You from Label to Table.

Slowing down helps you to better appreciate the taste and texture of your food. This can make you feel more satisfied with your meal, and less likely to overindulge.

"Mindful eating is great idea whether you need to lose weight, gain weight or stay the same, I'd encourage it no matter your diet," she said.

The Mayr Method goes a step further, recommending that dieters chewing each bite of food at least 40 times to slow down the eating process and promote better digestion.

That's unnecessary and likely to be a nuisance, according to Heikkinen.

"Most of us do eat too quickly, but 40 times is a lot and counting that is likely to take away from your enjoyment of the food," she said.

Rule: Eat high alkaline-food

Does it work? Yes, but not because of the reasons given by the Mayr Method.

The Mayr Method claims eating foods like fruits and veggies can help you lose weight by balancing your body's pH level.

There's no evidence this is true. The alkaline diet has previously been debunked since the body regulates its pH level naturally, and no combination of food can change that (nor would you want to!).

Swapping processed foods, sugary items, and red meat and replacing them with whole plant foods can help you lose weight simply because it can decrease calories while increasing the nutrients you consume.

"Eating more fruits and vegetables is always a good weight loss strategy," Heikkinen said. "If it's a way to get people to eat more of those, that's awesome, but it's not because of any alkaline effect."

Rule: Cut out dairy and gluten

Does it work? No.

Unless you're sensitive to either lactose (a sugar in dairy) or gluten, both Heikkinen and Taub-Dix said that there's no inherent benefit for weight loss if you swear off cheese, bread, and similar foods.

In fact, some of those foods can benefit dieters. Whole grains, for instance, can help you feel more full after eating, and cheese adds flavor, both of which lead to more satisfaction.

"It's not as if cutting out dairy or gluten is going to make your diet magical," Taub-Dix said. "This shines a light on how celebrities aren't setting good examples when they set their tables if they embrace restrictive diets with extensive do and don't lists."

Rule: No snacking between meals

Does it work? Maybe.

Experts are mixed about this one, since it really depends on the person. For people who struggle with distracted eating or stress-snacking, limiting food to mealtimes can cut out empty calories.

"I think this can be a good strategy for many people. Structure has a lot of value for people because it eliminates that struggle of should I eat or not," Heikkinen said.

On the other hand, small, regular snacks can prevent you from getting too hungry and overdoing it when you sit down to a meal.

"Successful diets include smart snacking," Taub-Dix said. "If you choose wisely, there's a good chance it helps keep your blood sugar stable."

Rule: Detox from sugar

Does it work? Yes, but it's not a "detox."

'Cutting out added sugar is a wise weight loss strategy, cutting out a source of calories without nutrients that don't tend to be very filling," Heikkinen said.

She added that "detox" is a pseudoscientific term that sounds more effective than it really is. And sugar isn't necessarily bad, particularly natural sources of sugar like fruit that are also loaded with nutrients.

"There's no one food that is the cause of being overweight. But it can be helpful and healthier to cut back on added sugar," Taub-Dix said.

Rule: Cut out caffeine

Does it work? No, and this one could backfire.

There's some evidence that caffeine, in the form of coffee and tea, can have benefits for your metabolism. There's no evidence cutting back can speed weight loss, so it ends up being an unnecessary restriction for people who enjoy those beverages.

"For weight loss there's so many things people are deprived of, why take away coffee which is low in calories?" Heikkinen said.

The exception is if you typically get your caffeine in the form of soda or sweetened coffee drinks, or have a habit of snacking at the same time.

In this case, being aware of your caffeine habits can help you eliminate some sources of hidden calories in your diet.

Rule: Don't drink water during meals or eat raw foods after 4 pm

Does it work? Definitely not.

In fact, the opposite is true. Heikkinen recommends taking sips of water or another healthy beverage between bites to help slow down your meal. And no evidence suggests there's anything wrong with eating fruits, raw vegetables and similar food later in the day, for digestion or any other reason.

"There's no reason to do this and I don't know where it comes from," Heikkinen said. "It's ridiculous to think that you can't eat a salad at dinner just because it's raw."

Rule: Eat a big breakfast and a small dinner

Does it work? Maybe.

There's some evidence eating early in the day can have a slight benefit for your metabolism.

And if you're eating a majority of your calories in the evening, you might benefit from spreading them out a bit more throughout the day. But for most people, this is a matter of preference. It's also possible to overdo it on this advice, if you're waking up to a heap of eggs, bacon, sausage and toast to start each day.

"It's good to think about timing your meals to when you're going to need the most energy," Taub-Dix said. "But a big breakfast can be unhealthy too. It's all about balance."

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