What Is the Ketogenic Diet, and Why Is It So Popular?

updated Jan 10, 2020
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For the past three years, the keto diet has been one of the most Googled, top Pinterest-performing weight-loss diets, and it continues to flood Instagram feeds. But the ketogenic diet was actually created almost 100 years ago as a way to treat epilepsy in children. It’s still used as a treatment today by many with epilepsy, but most know the keto diet for its quick weight-loss results. 

What Is the Keto Diet? 

On the surface, the keto diet is best described as a lower-carb version of a low-carb diet. In fact, the diet restricts carbohydrates to only 5 to 10 percent of daily calories, breaking down to between 20 and 50 grams a day for most people. But it’s also a very-high fat diet, prescribing that the bulk of one’s daily calories (70 to 80%) come from fat sources. This is significantly higher than any other popular diet, and leaves protein to make up just 15 to 25% of daily calories — so skinless chicken breasts are out, and bacon is in. 

Why so much fat? This is where we get a little science-nerdy. The goal of the keto diet is to put the body into a type of metabolic starvation known as ketosis, where it is forced to rely on ketone bodies for energy. Ketone bodies are produced when your body breaks down fat, but it will only do that when it doesn’t have enough carbohydrates. 

To back up just a bit, our bodies are fueled by carbohydrates — which get broken down into glucose, which is a sugar. That glucose is then stored by the body and used as fuel. But when the body is deprived of glucose (and all its stores have been used up), it must find an alternate energy source. 

That temporary source? Fat. The body breaks down fat into what are called “ketone bodies,” and uses those for fuel until it has access to carbohydrates again. This is why so many people have had success losing weight on the diet: The high-fat/very-low-carb combination aims to shift the body away from burning carbs and glucose and instead to break down and burn fat.

What Do You Eat on the Keto Diet? 

The ability to reach ketosis isn’t instantaneous. It happens after several consecutive days of strict adherence to eating very few carbohydrates (again, usually between 20 and to 50 grams per day). This means meals are based on meat, eggs, cheese, high-fat dairy (cream and butter), poultry, seafood, and plant-based fats like oil, nuts, seeds, and avocados

Low-carb vegetables that are high in fiber can also be eaten at meals (while keeping close tabs on even their minimal carb amounts, of course). This includes lettuce, spinach, kale, peppers, mushrooms, asparagus, broccoli, cauliflower, onions, green beans, celery, Brussels sprouts, and tomatoes. 

What’s off-limits? Keto doesn’t restrict specific foods — just carbs and sugar — but to maintain the tight requirements, many typical foods must be avoided. This includes most fruits, starchy vegetables (potatoes, carrots, corn), whole grains, legumes, refined grains, sugar, and dairy. 

More Ideas for Eating on the Keto Diet

Why the Hype?

Chances are you’re going to lose weight if you decide to go keto. Much like other lower-carb diets, such as Atkins and South Beach, weight-loss success on the keto diet has been proven to reap far more efficient and more effective results than traditional low-fat or Mediterranean-style diets. Individuals who have struggled on other diets may finally feel they’ve found something that works. Also, ketosis suppresses the appetite, while eating a high-fat diet keeps you full longer, so the desire to reach for, say, a 3 p.m. bag of potato chips is far less likely on the keto diet.

Other perks are that fewer grams of carbohydrates and sugar lead to fewer insulin surges, improved blood glucose levels, and better control of diabetic symptoms, according to a large portfolio of reputably published research. Also, when someone goes into ketosis, the brain uses ketones instead of glucose as fuel, and there’s a theory that these ketones might offer protective benefits to certain brain cells by being more energy efficient. Some research suggests this has the potential to directly inhibit neurological stress and to reduce risk for conditions like Alzheimer’s disease. 

But it’s important to realize that the keto diet isn’t an easy diet to follow. In the early stages, keto dieters often complain of “keto-flu” symptoms like headaches, dizziness, constipation, muscle cramping, bad breath, and loss of energy. Also, without whole grains, legumes, fruit, and a number of vegetables, the keto diet is typically low in fiber and it’s easy to become depleted of many vitamins and minerals found in these foods.

Lastly, to stay in ketosis, you must keep carbohydrate levels extremely low to actually shift your body’s metabolic fuel source. These metabolic adaptations can make it difficult to “switch” back and forth to regular carbohydrate-based meals and snacks without gaining weight and upsetting your metabolic balance. This means that if you plan to go keto, you need to plan to go all-in. 

Balance, consistency, and moderation all play a role in optimal health when adopting a healthy eating approach. This means it’s important to find an eating approach that works best for you, your routine, and your health goals, whether it’s keto or something else.

5 Things to Know Before Going Keto

1. It can be hard to sustain.

For people with brain disorders and diabetes, the keto diet can potentially offer health benefits and a way to manage and prevent certain symptoms. But studies are inconclusive and inconsistent. For someone who just wants to lose weight, the long-term effects are still unknown.

2. It’s more of a lifestyle than a diet.

When you go into ketosis, you’re actually shifting your body’s metabolic format. These metabolic adaptations can make it difficult to “switch” back and forth to regular carbohydrate-based meals and snacks without gaining weight and upsetting metabolic balance. If you plan to go keto, you need to plan to go all in.

3. It can be hard to achieve balanced nutrition.

Without whole grains, legumes, fruit, and a number of vegetables, the keto diet is typically low in fiber, and it’s easy to become depleted of many vitamins and minerals.

4. It eliminates added sugars.

Whether or not you decide to go keto, eliminating added sugars is something worth embracing. The same goes for adding more healthy fats (like avocado and olive oil) into everyday meals.

5. It should be done under a doctor’s supervision — especially at first.

If you decide to try the keto diet, it’s best to do so under a doctor’s supervision, at least at first. Understanding where good fats come from (nuts, avocados, plant oils) and recognizing what foods contain carbohydrates is essential for proper adherence and success.

The Bottom Line

Chances are you’re going to lose weight if you decide to go keto. And the brain-boosting, blood sugar-regulating benefits are well-supported, too. But ketosis is a state of metabolic stress; your body shifts into survival mode. It’s important to ask yourself what the overall goal of going keto actually is. Going in and out of metabolic ketosis is not good for you, nor are drastic ups and downs in your weight.

Balance, consistency, and moderation all play a role in optimal health, too — be cautious in how you approach anything with the word diet attached to it. The best diet is one that includes a lifestyle change that works best for you, your routine, and your health.

Note: The original article, written by Sidney Fry, MS, RD, has been updated by Carolyn Williams, PhD, RD. Carolyn Williams is a 2017 James Beard award-winning dietitian who has contributed to sites such as Cooking Light, EatingWell, Real Simple, Parents, Health, AllRecipes and Prevention. She has written three cookbooks, including Meals That Heal: 100+ Everyday Anti-Inflammatory Recipes in 30 Minutes or Less. You can find more about her on her own site as well as follow on her Instagram and Facebook.

Please note: This article is not an endorsement of nutritional ketosis as a best practice for sustained weight loss or supplement to medication.