Going 'keto'? Here's everything to know about the trendy ketogenic diet

The ketogenic diet is a high fat, low carbohydrate way of life.

If you’re looking to start the trendy diet in the New Year, here is what you need to know.

(MORE: Fast and simple keto recipes that will make you forget you're missing carbs)

What is the ketogenic diet?

The ketogenic, keto for short, diet was developed in the 1920s after it was noticed that after fasting, epileptics would experience a marked reduction in their seizures. The diet is designed to get your body into a state called ketosis whereby your body is so low on carbohydrates it starts burning fat for fuel.

Ketosis is also what the body does when fasting.

The diet’s proponents say it is the best way to lose weight without feeling hungry and that it increases energy levels.

(MORE: Inspiring grocery store coworkers lose over 200 pounds on keto diet)

What do people eat on the keto diet?

Keto dieters drastically cut carbohydrates to about 10 percent of their daily diet, which in some cases can be just 20 grams of carbohydrates per day.

That amount of carbohydrates is equivalent to one slice of white bread per day, Maya Feller, a New York City-based registered dietitian, told ABC News last year.

The amount of fat someone following the keto diet may consume in one day could be more than five times the recommended intake for daily fat for the average American, Feller says.

But she stresses that those fats should come from healthy fat food sources, such as olive oil and nuts.

MORE: This father of 3 lost 45 pounds through the keto diet during quarantine

"When I see people who are living the keto lifestyle, it’s rarely people who are eating fatty foods and doing nothing," she said. "They’re trying to keep themselves in ketosis and doing things like eating chicken and fish; they’re actually paying attention."

Foods that are “keto-friendly” include items like eggs, butter, unprocessed cheese, avocados, meat, low-carb veggies and nuts and seeds.

What to know before starting a keto diet

While the keto diet was one of the most searched diets in 2019 and the most searched in 2018, it tied for last in 2018 on the Best Diet Overall list released annually by U.S. News and World Report.

"One of our experts said, ‘Any diet that recommends snacking on bacon can’t be taken seriously as a health-promoting way to eat,'" Angela Haupt, assistant managing editor of health at U.S. News and World Report, told ABC News earlier this year.

"One of the concerns with keto is how high in saturated fat it is," Haupt said. "Our experts say the diet can be especially dangerous to people with severe diabetes, kidney disease and heart disease."

Other critics of the keto diet argue that it is nearly impossible to follow for a long period of time, and that it could lead to muscle loss or deprive the brain of its preferred fuel source: carbs.

Additionally, they argue that the majority of the research on the keto diet has not yet looked at the long-term effects it has on non-epileptic people over the course of 15 to 20 years.

Feller, who was not associated with the U.S. News and World report ranking, warns, "If we're talking about the majority of the country, [the keto diet] is not indicated and it's not going to be adhered to properly, and [it] is not sustainable. It's not ever my first-line recommendation."

People who want to make a change in their health should take a look at what they're eating and their dietary patterns, and then make modifications that are sustainable, Feller said, noting that dietitians are there to help.

How to get started

If you are ready to commit to the keto diet, Feller recommends talking with a qualified healthcare practitioner first to make sure the keto diet is safe for you and that you are correctly adjusting your macronutrients -- protein, carbs and fat.

"You have to have a real understanding of what that means in the context of your day and the context of what you have been eating," she said.

Feller also recommends making sure you get blood work done regularly, particularly a lipid profile.

Editor's Note: This story was originally published on Dec. 28, 2018.