It took a while, but by now most of us know that fat is not the enemy, that there are certain kinds of fat that can actually help your heart, and that it need not be obliterated from your diet if you’re trying to lose weight. In fact, for some people, fat is actually the superhero of their diet—and chowing down on olive oil, butter, and heavy cream is the key to watching the scale dive lower and lower, without feeling hungry or deprived. But can a diet heavy on the heavy cream turn out to be not unsafe—and maybe even good for you? We consulted top-shelf, unbiased sources that specialize in diet and nutrition, and were surprised to find that the answer is a resounding yes.
First, the basics about the diet. It’s called a ketogenic diet, one that’s heavy on fat, moderate in protein, and extremely light in carbohydrates (typically less than 50g a day). The way it works involves a neat little trick of your body’s own biology, says Charles Passler, a nutritionist in New York City, who works with many of the top models you see sashaying down the runways at fashion week. (Bella Hadid is among his clients, as are many of the Victoria’s Secret models, including Adriana Lima.) The body typically burns carbohydrates—aka glucose—for fuel. But if you give your body little to no carbohydrates, it will go into ketosis. This is a state in which fat stores in the body are broken down into ketones, which then fuel the muscles and brain.
If that sounds a bit odd, it’s not, says Passler. “The human body is designed to be able to handle times of food scarcity,” says Passler. “The trouble is, we currently have access to food 24/7, but our physiology hasn’t caught up with that yet. Say you have breakfast at 8 a.m., and then it’s 1 p.m. and you think you’re starving, that’s just five hours. The only reason you feel that way is because you had a meal with carbs in it and your blood sugar levels have crashed, which leads you to believe your body actually needs more fuel. We make the mistakes of thinking we are starving when in fact, it’s a carbohydrate roller coaster.”
By contrast, when you’re on a ketogenic diet, you have more stable blood sugar and you become a fat-burning machine. Not only that, but you’ll see the difference pretty quickly. “That’s because a big part of the glycogen in your body tissues is made of water,” says Passler. After that stash is exhausted, any puffiness or bloating will be gone and your body will immediately shrink a bit. (This is also why many body builders rely on ketosis to give them a cut look during competitions.) Of course, that water-weight is not lost permanently; if you go out of ketosis, it can return. The fat you burn, however, is gone, baby gone.
Suzanne Ryan, 33, had tried just about every other diet out there before she stumbled on chatter about the keto diet in a sub-Reddit thread, in 2015. After just one month on the diet, she had lost 21 pounds; a year later, 100 pounds. Two years later, she’s down over 120 pounds but up over 100,000 Instagram followers, and while she sometimes misses being able to eat things like fruit (more on that in a second), “for the most part my tastes and preferences have changed so much. Once you break the sugar addiction you are still eating really delicious and flavorful foods.” She’s so passionate about this way of life she has created a blog, KetoKarma.com, and will publish a cookbook, Simply Keto, in Dec.
Some of the diet specifics may surprise you. For instance, not all vegetables get a complete green light. You can have as many leafy greens as you want, but certain veggies, like potatoes and onions, are higher in carbs and should be moderated. For fruit, you can eat most berries, but should steer clear of tropical fruits and even prosaic stuff like apples and orange, since they are high in sugar. For meat and cheese and other dairy—as with anything you buy—keep an eye out for added sugars you might forget about; cured meats like honey-roasted ham, for instance, or flavored yogurts, aren’t a great choice.
A typical keto dieter’s day is about 60-80% fat, 20-30% protein, and 10% carbohydrates. For Ryan, her eating plan may look like this: Coffee in the morning with heavy cream, plus two scrambled eggs with avocado; lunch is a lettuce-wrapped sandwich of egg salad or turkey or ham with mayo; dinner is chicken, steak, or seafood with cauliflower mash or veggies with butter. “With keto I eat a lot more whole foods, non-starchy veggies, things high in fat (avocados, butter, coconut oil) and moderate protein.”
And those with less weight to lose than Ryan—but with photo shoots to prep for or certain chronic illnesses—also sing the diet’s praises, saying it’s far less difficult or restrictive than you might imagine. “You can have so many filling foods on this diet, and you feel great, especially in the morning,” says Sarah Biehler, a model and actress in New York City, who works with Dr. Passler. The diet’s speed is a huge selling point: “Weight loss is easier with a keto diet than with other diets,” says Biehler. “And you see progress quicker, which makes you more motivated. You can make a keto-friendly version of any meal.”
While there are some critics who knee-jerk fret about how a high-fat diet can impact your cardiovascular health, if you look more carefully at it, this can be a safe, effective diet, says David Ludwig, MD, PhD, a professor of nutrition at Harvard University, and author of Always Hungry. “Ketogenic diets are actually great for triglycerides and HDL levels, and can lower insulin levels,” but it can definitely be different for everyone. Some people see an increase in cholesterol and others don’t, says nutritionist Mascha Davis, MPH, RDN, owner of NmadistaNutrition.com in Culver City, CA, and a spokesperson for the American Academy of Nutrition and Dietetics. “If heart disease is in your family, be very careful with this diet. It’s important to get your lipid levels tested and to consult with a dietitian if you’re trying this, or any, diet.”
Ryan found that her body reacted well to keto. When she went to visit her doctor after being on the diet for a year, her blood work showed that her cholesterol levels and rations were better than ever. “She was unsure of my doing keto at first—she’d always handed me sheets about low-fat diets—but now she has even recommended keto to some of her other patients,” says Ryan.
Getting through the first few days or week can be the biggest hurdle, notes Passler, as your body goes through the remaining glucose and then converts to ketones. (It’s called the “keto flu”: think fatigue, brain fog.) But once you get into ketosis— some dieters actually use at-home, test strips to check their urine for the presence of ketones—you may experience what some people call the “keto float.” Ludwig himself tried the diet, and found that it gave him great energy and mental clarity, not to mention a slimmer physique.
There are some concerns, however, with loss of muscle mass on keto diet, says Davis. Some research has shown that even if your protein intake remains constant, a low-carb diet may promote muscle loss. In a Dutch study, participants were given three diets (high-carb, moderate-carb, low-carb) and moderate protein. “The study found that those following a low-carb diet experienced increased muscle breakdown, because when we eat carbohydrates, we produce insulin which promotes muscle growth. So, when we skip the carbs all together, muscle glycogen stores get depleted, we lose out on those muscle-building opportunities,” says Davis. Translation: “Don’t even think about continuing your high intensity-training regimen on this diet,” says Davis. Careful snacking can help you get around this, though, says Passler. “If you eat something containing carbohydrates just before you workout, so your body can burn that right away.”
A large-scale study published last month in the Lancet gave keto devotees reason to toast. The researchers found that people eating loads of carbs had a nearly 30% higher risk of dying during the study than people eating a low-carb diet. Compare that to those eating high-fat (or keto) diets: the study found they had a 23% lower chance of dying during the seven years of follow-up compared to people who ate less fat.
The biggest issue, say some experts, is sustainability in the long term—at least from a lifestyle perspective. “The diet is sustainable if you are a planner,” says Gabrielle Lyon, DO, an osteopathic physician and integrative medicine specialist at The Ash Center in New York City, “in the sense that you would need to make sure the meals you eat are within the keto ‘sweet spot.'” If you are a person that eats out a lot you will probably find this diet difficult to follow successfully. And then there’s something Lyon calls “palate fatigue”— being sick of the same food over and over again. Successful keto dieters, however, counter that the weight loss is better than any carb tastes, and that you can make any recipe keto-friendly—a virtual have-your-keto-cake-and-eat-it-too scenario. Bottom line: It’s just not for everyone, and it’s not always something you can stick to forever.
Before you start piling on the butter and kicking carbs to the door, study up and keep a few more things in mind. Keto diets can leave you dehydrated (as the glycogen is depleted your body will not hold as much water), says Lyon, so you should take a high quality multivitamin/mineral supplement, particular to replace lost electrolytes like sodium and potassium. “I would encourage all keto dieters to salt food, try Himalayan or Redman Real Salt, and supplement with extra magnesium,” says Lyon. You also might consider a fiber supplement too, says Lyon, since the diet can cause constipation, at least at first.