Those of us who grew up in the age of Snackwell cookies and reduced-fat peanut butter may still be fighting the fear of eating food containing fat. And with the low-fat diet trend now seemingly swapped for butter and bacon crazes, it’s difficult to know what to think of this misunderstood macro anymore.

Let’s get one thing straight: Our bodies need some fat in order to survive. “Fat helps us absorb the vitamins D, A, E, and K, and is important for our immune function, hormonal balance, and our brain (which is 60 percent fat itself),” says Brian St. Pierre, M.S., R.D., C.S.C.S., director of performance nutrition at Precision Nutrition. Still, if you surf the Internet for just a few minutes, you’ll see that the pre-millennial anti-fat campaigns have been replaced by the high-fat or ‘ketogenic’ diet. If you’re considering trying this style of eating for yourself, there a few things you should know first.

What Does ‘Ketogenic’ Even Mean?

‘Ketogenic,’ the term used to describe the increasingly trendy fat-based style of eating, refers to a specific metabolic state that dieters are trying to shift their bodies into. “Typically, our bodies run on glucose, which comes from carbohydrates,” explains St. Pierre. “But when fewer than 10 percent of our calories come from carbs, our bodies run on ketones, which come from fat in food or stored in our bodies.” Think of it like a backup generator.

What’s The Appeal?

The keto diet shifts the body into that burn-fat-for-fuel mode, which is otherwise achieved by fasting, says St. Pierre. Yep, ketosis is also how your body reacts to starvation, using stored body fat for energy.

While some turn to ketogenic dieting hoping to lose weight—it’s been hypothesized that ketogenic dieting boosts your metabolism because it’s harder for the body to use ketones for energy—your body does adapt, notes St. Pierre.

How Do You Actually Eat Like This?

Eating fewer than 10 percent of your daily cals from carbs requires a lot more than cutting out bread. To shift your body into ketosis, you can kiss fruit and starchy veggies like carrots or squash goodbye. “You need to get around 75 percent of your calories from fat for up to several weeks in order to achieve ketosis,” says St. Pierre. “That means you’ll also need to cut back on protein to somewhere around 20 percent of your total calories, because you can convert some of its amino acids into glucose.”

Here’s what a day of keto eating might actually look like:

For breakfast, you’ll eat about three eggs and some bacon, cooked in plenty of butter, says St. Pierre. You may be able to throw in some avocado and cauliflower. For lunch, you’ll go for a smaller (say three-ounce) portion of fatty meat, again cooked in butter, with a small spinach salad, crumbled cheese, and lots of dressing on the side. Then, for dinner, you’ll eat another small helping of fatty meat—and yep, more butter—with broccoli doused in olive oil and a handful of nuts.

Related: Find a keto supplement to add to your daily routine. 

Like you’re probably thinking, this style of eating is tough to stick to.

It’s Not All Butter And Rainbows

Sure, the idea of loading up on bacon sounds pretty good at first—but there are some downsides to a ketogenic diet you should know about before you buy yourself a Costco-sized tub of lard.

“Long-term, it’s very possible that you’ll miss out on fiber, protein, vitamins, and minerals that your body needs,” says St. Pierre. Ditching fruit may leave you wanting for phytonutrients and the antioxidant vitamin C, while cutting back on protein may lead to a zinc, copper, or iron deficiency, he explains.

Women of reproductive age, whose bodies are more sensitive to calorie and carb intake to support any potential buns in the oven, may especially want to think twice before going keto, says St. Pierre. “If women don’t get adequate carbs, their bodies may shut down reproductive ability,” he says. When women deprive their bodies of the energy source they typically run on, survival takes priority over reproduction, and hormone function and menstrual cycles become irregular.

St. Pierre also cautions anyone with a history of disordered eating from following a restrictive diet like keto. “These extreme diets feed into the cycle of guilt, restriction, and binging, because they’re so hard to consistently follow,” he says.

How To Enjoy Fat Without Going Hardcore

Some people say they feel great following a super high-fat diet, but most of us are probably best off sticking to a diet more balanced in carbs, protein, and fat. (What’s a life without bread?)

Healthy fats like olive oil, avocados, tree nuts, and seeds deserve a spot on your plate. “We recommend one to two thumbs of healthy fats at each meal,” says St. Pierre. (The size of your thumb is roughly a tablespoon.) That’s four to six thumbs of fat per day for a moderately active woman and six to eight thumbs for a moderately active man.

“Ultimately, if you’re really interested in trying keto, there won’t be long-term harm from trying it out for a month or two,” says St. Pierre. “Just make sure to mix up your fat sources and try to eat a variety of vegetables, and keep a close eye on how you feel, look, and perform.”

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