Kim and Kourtney have raved about it, a ton of Victoria's Secret models are fans, and it's been described as a way to "turn the body into a fat-burning machine."
But it's also been branded a fad, and some even claim it's dangerous. So is the Keto diet 2018's Beyonce maple syrup diet? We asked the experts what the fuss is all about.
What does Keto mean?
To give it it's full name, the Ketogenic diet is a way of eating that causes the body to make energy from things called ketones, rather than using the simple sugars from carbs in our diet. It involves "starving" the body of those type of foods to make it work harder, Nutritionist Sandra Greenbank explains:
"The body has two different ways of using the food we eat to make energy. The easiest is to use glucose—that's what's in sugar and carbs in our food—and it's quite low intensity for the body.
"The other way is using ketones, which are produced in the liver, for energy. It's a natural state you go into when food supply is low, a protective way for the body to keep going. And it's very effective for quick weight loss. The weight literally drops off."
Are there health benefits beyond weight loss?
"It's good for those who are very obese, to help them start to lose weight, especially because it can be really motivating to see results quickly. It has the potential to reverse prediabetes, improve cholesterol, and it can also be helpful if you have PCOS by reducing your sensitivity to insulin.
"It also reduces inflammation, which drives a lot of diseases like cancer and arthritis, and some people also say it makes them feel more mentally sharp and gives them focus."
Why is it controversial?
Personal trainer Max Bridger doesn't recommend the Keto diet: "It isn't something we think is ideal for health, fat loss, or muscle gain goals. It's unsustainable; it's not compatible with normal life, especially when you consider things like family, friendship, and professional circles, which all make it very difficult.
"In theory, eating this way causes the body to become more efficient at burning stored body fat and you lose weight quickly. But in reality, ketosis is unachievable for many people—even on a true ketogenic diet—due to their genetics."
Susan, a nutritionist, agrees that the diet can be unhealthy, too: "It's an extreme way of eating that doesn't fit in the norms of society so it's quite difficult to do properly and can be very antisocial. And some people believe it can be quite dangerous as it's putting your body into starvation mode.
"I would certainly caution anyone who has any kind of health diagnosis to work with a nutritional therapist," she advised. And you have to be sensible. You could just live on cheese and meat and forget your vegetables, but you'd miss out on vitamins. The quality of the meat matters too—eating bacon and sausages all day long obviously isn't healthy.
"It can also be hard to digest all this rich food, it's harder work for your body. And I do believe that women need more carbs than men to help our hormones so you need to pay attention and add more if your body’s asking for it."
How do you do it safely?
"Everyone is different, so the level of carbs to get one person into ketosis is different to another," says Susan. "It depends on metabolism, genetics, size, and lifestyle."
If that hasn't put you off, and you still think this sounds like something you want to try, it's vital to do your homework and prepare fully.
Susan says: "If you want to do it properly you really have to plan ahead. You can't do it off the cuff."
The first week, while your body's adjusting it can actually make you feel quite ill—nicknamed 'the keto flu.' You have no energy and feel awful, then suddenly it kicks in and you feel amazing."
- Eat Well.
"What you're doing is shifting your intake of carbs, fat, and protein to 70 percent fat, five percent carbs, and 25 percent protein. That's 20 to 30 grams of carbs a day, and bear in mind a slice of bread is 15g. You'll need to get your calculator out, because there are carbs in chicken, for example, so that will count towards your total.
"You cut out grains, sugar, fruit, cereal, tubers (potatoes and vegetables grown underground). And you do want to eat meat, fish, veggies grown above ground, cauliflower, broccoli, kale etc. Plus high-fat dairy, nuts, seeds, olives, oils, avocados, anything fatty really. It's quite hard to do as a vegetarian and especially if you're vegan," Susan adds.
"It's really important to make sure you're not missing out on essential nutrients, as that could harm your health," she says. "The grains that you're cutting out do contain a lot of good things—B vitamins, for example. I think people should probably be on a good quality multivitamin anyway but make sure you're still eating a good range of foods and lots of vegetables."
- Check Your Pee.
"The way to know if you're in ketosis is using keto sticks. You pee on them and the color tells you what your level is. You don't have to be at the highest level, just being in ketosis is enough. If you're at the higher end, add in more carbs," advises Susan.
- How Long Should You Do It?
"It’s a real commitment and I would say if you really need to lose a lot of weight, do it for a month, then reintroduce carbs at a low level for maintenance. More than that and you need to work with a pro. It's not something that you can be on forever, unless you have very specific health needs. And also if you're pregnant or trying to conceive, or are on any other kind of medication, seek expert guidance."
Max adds: "It's not superior to any other form of calorie-controlled diet in its outcome."
It sounds boring and isn't what a celebrity trainer trying to sell you something new and sexy will say, but all diets rely on you being in a calorie deficit to work—it's just about finding a style of eating that is healthy and most suitable and enjoyable for you."
This article originally appeared on Cosmopolitan.com/uk. Minor edits have been made by the Cosmo.ph editors.