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What is the Keto Diet? A Review of the Latest Diet Craze


The ketogenic diet is everywhere you look.

“It’s a hot topic,” said Leah Cassella, RD, LDN, a registered dietitian and member of the Penn Bariatrics team. “But the question is, ‘is it sustainable?’”

For the past few years, celebrities have touted this high-fat, low-carb diet’s perceived ability to help followers shed pounds, boost energy and improve sleep. However, there’s little scientific evidence to back up those claims, especially long-term.

“I think as a culture, we tend to demonize one food group and praise another at different times, and right now we’re demonizing carbs and praising protein,” said Penn Medicine Bariatric Program Manager, Colleen Tewksbury, PhD, RD. “It’s popular now, but the trend constantly shifts.”

What is the Keto Diet?

The ketogenic diet is all about cutting out carbohydrates and eating more fats. Followers derive 75% of their daily calories from fat, 20 percent from protein and only 5 percent from carbohydrates. This is meant to induce ketosis, a metabolic process in which your cells don’t have enough carbohydrates to use for energy, so your body creates ketones and burns fat instead.

“The question is whether or not you are actually getting yourself into a ketogenic state, or if you’re just following a low-calorie, low-carb diet, which can also be effective,” Tewksbury said.

“You’re eating very few veggies, little to no fruits, absolutely no grain products, some meats but not much. It’s mainly a fat-based diet to reach a truly ketogenic state and maintain it. It just doesn’t sound pleasant to most.”

If ketosis is reached, it can lead to short-term weight loss. However, the keto diet is extremely restrictive, making it hard to follow and difficult to maintain.

“I think one of the biggest things is the sustainability factor – is it something you can keep up with, is it safe to keep up with six months or a year from now?” Cassella said. “I’ve seen it in a handful of our patients, they try it for a month or two and lose weight, and then they come back in three months and they have regained that weight – plus more – because it isn’t sustainable.”

Who Can Benefit From It?

The ketogenic diet was originally developed in the 1920s to help pediatric epilepsy patients control seizures, but in the past few years, it has become a trendy way to lose weight.

“The biggest thing about the ketogenic diet when it comes to the general population is that there is little or no evidence to support it,” Tewksbury said. “The primary group that the ketogenic diet has been studied in are children with epilepsy, and it has been shown to be very effective in reducing seizures in that population.”

It’s important to realize the diet wasn’t created to be a low-calorie diet, but has been modified for weight loss.

“It hasn’t been scientifically proven to be an effective mechanism to lose weight,” Tewksbury said, noting there are a few studies occurring now surrounding the ketogenic diet and weight loss. “My job as a dietitian is to let people know that the science isn’t there. That’s my biggest qualm – It’s not evidence-based and it’s being used for weight loss.”

Is There a Better Way?

“We know [weight loss] comes down to caloric restrictions,” Tewksbury said. “If the ketogenic diet helps someone restrict their calories, that’s great and will likely lead to weight loss. But if not, that person may just be spinning their wheels.”

And while Tewksbury doesn’t discourage patients from trying different diets, she asks that they take a realistic look at why and how they plan to implement a routine.

The healthiest approach to weight loss is a comprehensive lifestyle change.

Create a plan that provides long-term benefits to your health and set realistic goals that include exercise. If the diet you are following is too restrictive and meant as a quick fix, it’s a red flag.

“To help patients start focusing on lifestyle changes, we work with them to set small, realistic goals that they can then build upon,” Cassella said. “For example, maybe one week you can focus on replacing three sugary drinks with water, then the next week you can replace six sugary drinks with water.”

These small changes compound and become new, sustainable habits.

“Tracking your progress and your goals is a great way to stay accountable and motivated,” Cassella said. “It can be difficult to break that ‘diet mentality,’ but developing habits that you can realistically keep up with, can result in long-term success.”

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