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What's the Science Behind Keto?

By Stephanie E - Jenny Craig

Reviewed by Briana Rodriquez, R.D.


Which diet is very low-carb, high-fat and based on some surprising science? If you guessed the ketogenic diet, also referred to as keto, you’re right! It’s not hard to find someone touting the latest science behind the keto diet. But if you’re wondering what to believe, you’re not alone. We've pulled together the most up-to-date science behind the keto diet and spoke with Jenny Craig's Registered Dietitian, Briana Rodriquez, to learn more and help you decide if it’s the right weight loss plan for you — or if something else could be better.

Where did the keto diet come from?

Get this: The keto diet didn’t start off as a method to lose weight. It was originally used to treat epilepsy by reducing seizures in the 1920s. Dr. Russell M. Wilder1 suggested patients could experience the benefits of fasting in a different way — by following a “ketogenic diet,” a term he coined while at the Mayo Clinic.2 Over time, using the keto diet to treat epilepsy became less common. Keto’s spike in popularity came many decades later — this time, for weight loss. 

Now, the keto diet is one of the trendiest weight loss strategies: It clinched the top spot for most-searched diet in 2018, according to Google’s Year in Search.3

So, what makes the keto diet so popular? The proof might be in the (full-fat) pudding. 

The science behind the keto diet

The keto diet is a high-fat, moderate-protein, very low-carb approach to weight loss. But before you start loading a plate full of steak and bacon, you might want to pump the brakes. Here’s what a registered dietitian really thinks about the keto diet.

How the keto diet works

  1. Start eating plenty of fatty foods and fewer carb-heavy ones. The human body’s main source of energy is glucose, or blood sugar, which comes from the food you eat.4 By depleting your body of glucose, your body will be forced to find another source of energy, and you may be able to lose weight. People who follow the keto diet heavily reduce the amount of glucose that’s available for energy. To do that, they cut back on carbohydrate-rich foods and turn to high-fat, low-carb meals instead.
  2. Achieve ketosis. The goal of the keto diet is achieving and maintaining a natural process called ketosis. During ketosis, ketone bodies (or ketones), produced by stored fat, replace glucose as the main energy source.5 The body is always producing small amounts of ketones, but during ketosis, that number increases.6
  3. Maintain ketosis. This is the tricky part. To keep the body in ketosis, it’s important to continue avoiding most types of carbohydrates. Getting the right ratio of fat, protein and carbs at each meal can be difficult and potentially expensive, depending on the amount and quality of the food you eat. Many people rely on online calculators to determine the servings that work for them. 

What’s in a typical keto meal?

Photo by Olga Miltsova on iStock

keto meal with egg avocado bacon and cheeseThe keto diet focuses on the three macronutrients: carbs, fat and protein. 

There are many variations of the keto diet, but one that’s very common is the standard ketogenic diet. Your daily macronutrient totals will consist of 75% fat, 20% protein and just 5% to 10% carbohydrates.7

While you’re following the keto diet, you’ll definitely need to be choosy about the carbs you eat. You’ll only have about 20-50 grams of carbs per day8 — that’s about what you’ll find in one large banana,9 says Briana Rodriquez, Registered Dietitian Nutritionist at Jenny Craig.

What you’ll find in a keto meal: Eggs, meat, fish, nuts, seeds, full-fat dairy products, butter, oils, avocado, small amounts of green vegetables and berries.

What you won’t find in a keto meal: Most types of fruit, baked goods, cereal, pasta, potatoes, beans, legumes, refined sugar, starchy vegetables, alcohol and honey.

“Carbohydrate-rich foods, like fruits, vegetables and whole grains, are important sources of glucose in a well-balanced diet,” explains Rodriquez. “They’re also nutrient-rich foods that can support your weight loss and health goals.” 

The keto diet tends to restrict these foods, which makes it easy to miss out on dietary fiber. Fiber is important for healthy digestion and can help you feel full without loading up on a ton of empty calories.

“The fat and protein you’ll have with the keto diet can naturally help you to feel satisfied, too. But eating too much butter, lard and cheese can add unnecessary saturated fat to your diet,” she says. 

Eating an excess of foods rich in saturated fat is linked to heart disease and increased LDL cholesterol, according to experts at Harvard Health.10



Keeping up with the keto diet

Modern versions of the keto diet focus on fast, short-term weight loss. While that may seem promising, studies often lack research to conclude the long-term health effects or benefits.11


So, what does the science behind the keto diet say?


You may not experience true fitness gains. A study on athletes who followed the keto diet for 12 weeks had mixed results. While exercise performance didn’t decrease, the athletes did not improve their performance by the end of the study.12 In addition, the researchers suspect following the keto diet for long periods could negatively affect increases in muscle mass.

In a separate study on world-class race walkers, participants who followed a ketogenic diet developed early signs of bone loss.13

You might have better success with a different approach. Keto’s claim to fame is its ability to burn body fat quickly and efficiently. But that’s not always the case. A small study of overweight and obese men placed participants on two different diets with the same total calories. A high-carb, lower fat diet was first; a lower carb, higher fat ketogenic diet was next. Researchers noted following the keto diet didn’t result in increased body fat loss, as they’d thought. And more surprisingly, researchers think a significant portion of weight lost during keto was actually water weight, not fat.14

You could regain the weight you’ve lost. Although following the keto diet could result in weight loss, the results may not last. The study found that participants’ weight loss peaked after five months of following the keto diet. After that, they slowly regained weight during a maintenance period.9,15

Keto is the quick fix of the moment to help people lose weight, but it could be difficult to maintain a healthy lifestyle long term. 

“The foods you eat while following the keto diet matter,” says Rodriquez. “If you’re trying it out on your own, it could be difficult to get the right balance of macronutrients to maintain ketosis for long periods.”


It's clear to see that the science behind the keto diet is still evolving. In the end, it's best to choose a diet that works for lifestyle and is sustainable. 

If keto’s out, what’s in?

jenny craig pulled pork and veggies entree on plateIf you can’t imagine a future without pasta and bread, don’t worry — there’s a way to tap into the benefits of keto without being so extreme. A different type of diet may offer the same weight loss benefits and could be a more sustainable option.

Jenny Craig offers a more balanced, convenient approach to weight loss with delicious low-carb options. Jenny Craig's chef-crafted meals don’t require any carb-counting, ingredient measuring or lengthy prep work.

You won’t have to figure out a game plan alone. Jenny Craig’s weekly menus are designed by a knowledgeable nutrition team, and you’ll connect with a personal weight loss coach who can guide you throughout your journey.

And unlike the keto diet, you won’t have to stay low-carb forever. Once you reach your weight loss goals, the Jenny Craig program will start adding more healthy carbs into your menus. You’ll learn healthy habits for life — so you can eat what you love, even while maintaining your weight. 

Weight loss shouldn’t be complicated — and it doesn’t need to be! Get started with Jenny Craig today!




[1] http://www.jbc.org/content/52/2/393.full.pdf
[2] https://onlinelibrary.wiley.com/doi/full/10.1111/j.1528-1167.2008.01821.x
[3] https://trends.google.com/trends/yis/2018/US/
[4] https://medlineplus.gov/bloodsugar.html
[5] https://www.ncbi.nlm.nih.gov/books/NBK499830/
[6] https://www.ncbi.nlm.nih.gov/books/NBK493179/
[7] https://www.healthline.com/nutrition/ketogenic-diet-101#types
[8] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6371871/
[9] https://fdc.nal.usda.gov/fdc-app.html#/food-details/341529/nutrients
[10] https://www.health.harvard.edu/staying-healthy/the-truth-about-fats-bad-and-good
[11] https://www.health.harvard.edu/blog/ketogenic-diet-is-the-ultimate-low-carb-diet-good-for-you-2017072712089
[12] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5969192/
[13] https://www.frontiersin.org/articles/10.3389/fendo.2019.00880/full
[14] https://academic.oup.com/ajcn/article/104/2/324/4564649
[15] https://academic.oup.com/ajcn/article/87/1/44/4633256

Stephanie Eng-Aponte

Stephanie Eng Aponte
Stephanie Eng-Aponte is a copywriter for Jenny Craig and has written for the health and wellness, tech, and environmental industries. Stephanie graduated from Rutgers University with a Bachelor of Arts degree in Journalism and Media Studies. They employ an “eat first, write later” approach to food blogging and enjoy the occasional Oxford comma. Outside of writing, you can find them photographing a muttley crew of rescue pups, brewing kombucha, or exploring San Diego.

Favorite healthy snack: green apple slices with sunflower butter



Reviewed by Briana Rodriquez, RDN

Briana Rodriquez, RDN
Briana is a Registered Dietitian Nutritionist and Certified Personal Trainer for Jenny Craig, based in Carlsbad, California. She is passionate about utilizing food as functional and preventative medicine. Guided by a simplistic and optimistic approach, Briana’s philosophy is to help people improve their health and achieve their goals through the development of sustainable habits to live a healthy life. In her free time, you can find her strength training, indoor cycling, coffee tasting, and at local eateries with her husband and two dogs. 


Favorite healthy snack: peanut butter with celery alongside a grapefruit-flavored sparkling water (so refreshing!) 



This article is based on scientific research and/or other scientific articles and was written by an experienced health and lifestyle contributor and fact-checked by Briana Rodriquez, RDN, Registered Dietitian Nutritionist at Jenny Craig.


Our goal at Jenny Craig is to provide the most up-to-date and objective information on health-related topics, so our readers can make informed decisions based on factual content. All articles undergo an extensive review process, and depending on topic, are reviewed by a Registered Dietitian Nutritionist (RDN) or Nutritionist, to ensure accuracy. 


This article contains trusted sources including scientific, peer-reviewed papers. All references are hyperlinked at the end of the article to take readers directly to the source. 


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