Image of keto diet foods such as avocados and nuts

The keto diet is short for “ketogenic diet.” It’s a high-fat diet that has the potential to turn your body into a fat-burning machine. 

The keto diet changes the way your body converts food into energy. Normally, your body turns carbohydrates (think bread and pasta) into glucose for energy. Eating a lot of fat and very few carbs puts you in ketosis, a metabolic state where your body burns fat instead of carbs for fuel.[1]


When your body can’t get glucose from your diet, your liver turns body fat and fat from your diet into molecules called ketones, an alternative source of fuel. This puts you into ketosis, aka prime weight loss mode.

According to some metabolic experts, you’re in the state of ketosis when your ketone levels measure 0.5-3.0 millimoles per liter. The keto diet is one way to get your body to make ketones. Other ways to run on ketones include intermittent fasting and using up your glucose reserves by exercising. 


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The keto diet quickly boosts weight loss because your body turns fat from your diet and your internal fat stores into ketones. And unlike glucose, ketones can’t be stored as fat because they aren’t digested the same way. 

That’s surprising, right? For decades, you’ve heard that fat makes you fat. Your body is actually built to use fat as an alternative source of fuel. For most of history, people weren’t eating three square meals and snacks throughout the day. Instead, humans would have to hunt and gather their food, and they learned to thrive when there wasn’t any food available, sometimes for days on end.[4] To keep going, their bodies used stored fat for energy. Thanks, evolution.


  • Burns body fat: When you’re on keto, your body uses stored body fat and fat from your diet as fuel. The result? Weight loss.[5]
  • Reduces appetite: Ketones suppress ghrelin — your hunger hormone — and increase cholecystokinin (CCK), which makes you feel full.[6] Reduced appetite means it’s easier to go for longer periods without eating, which encourages your body to dip into its fat stores for energy. More research needs to be done in the area of appetite and ketosis, but it seems a lot of people experience reduced hunger. 
  • Reduces inflammation: Inflammation is your body’s natural response to an invader it deems harmful. Too much inflammation is bad news because it increases your risk of health problems. A keto diet can reduce inflammation in the body by switching off inflammatory pathways and producing fewer free radicals compared to glucose.[7] [8]
  • Fuels your brain: Ketones are so powerful that they can provide a good portion of your brain’s energy needs, which is way more efficient than the energy you get from glucose. Did you know your brain is made up of more than 60 percent fat?[9] That means it needs a lot of fat to keep the engine humming. The quality fats you eat on a ketogenic diet do more than feed your day-to-day activities — they also feed your brain. 
  • Increases energy: When your brain uses ketones for fuel, you don’t experience the same energy slumps as you do when you’re eating a lot of carbs. When your metabolism is in fat-burning mode, your body may tap into its readily available fat stores for energy. That means no more energy crashes or brain fog. Ketosis also helps the brain create more mitochondria, the power generators in your cells.[10] More energy in your cells means more energy to get stuff done. 
  • Curbs cravings: Fat is a satiating macronutrient. You eat a more smart fats on keto, so you feel fuller, longer.[11][12]


Image of a pink bathroom scale on a pink background

So, how exactly do you lose weight on keto?

When you start eating more fat and cut out the extra carbs (think sugar, bread and pasta), you tend to experience fewer blood sugar swings and cravings that plague most people on the Standard American Diet. When your body runs on ketones for fuel, it has a steady supply of energy in the form of body fat. When your body relies on glucose, it needs a regular hit of carbs to keep it going. 

Ketones may help control your hunger and satiety hormones so you feel satisfied and full, not hangry. That means fewer cravings, more energy and increased fat-burning. Here’s how it works.


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Ketones impact cholecystokinin (CCK), a hormone which makes you feel full, and ghrelin, the “hunger hormone.”

  • CCK: Your intestines release CCK after you eat, and it is a powerful regulator of food intake — so much that one study injecting obese men with CCK will cause them to cut their meals short.[13] Ketones increase CCK levels so you actually satisfied after meals.
  • Ghrelin: Ghrelin is called “the hunger hormone” because it increases appetite. It’s released from your stomach and intestines, with blood levels reaching their highest point when you fast. When you finally eat a meal, ghrelin drops in response to nutrients circulating in your blood. Ketosis suppresses the increase in ghrelin levels that occur with weight loss.[14] [15] So, when you’re in ketosis, you aren’t constantly thinking about your next meal.


image of neurons

One of the reasons old-fashioned, calorie-restricted diets tend to fail is because these diets make you really hungry and cause food cravings. 

Cutting calories to lose excess weight changes your hormones that control hunger and satiety. After you starve yourself enough to lose some weight, your brain and gut start making your hormones work against you. [16] [17] Your hormones scream, “Eat more and gain that weight back!” So you do. And so begins a lifetime of yo-yo dieting. 

But it doesn’t have to be that way. Skip the whole calorie-restriction, hungry-all-the-time thing, and just use ketosis to its full advantage without making yourself hungry. As long as you’re eating a higher percentage of quality fats, moderate protein and just enough carbs, you’ll feel satisfied and energized — not hangry. No calorie-counting required.


The keto diet is pretty simple: Eat mostly healthy fats (about 75 percent of your daily calories), some protein (about 20 percent) and a very small amount of carbs (about 5 percent). This is the general breakdown that a lot of keto beginners follow, but you may have to adjust your numbers and test your ketones to see what works for you.

Choose lower-carb foods such as meat, fish, eggs, vegetables and quality fats. Check out this detailed keto food list and browse these keto recipes for meal ideas. Most people do best eating somewhere between 30-150 grams of net carbs daily. 

Net carbs” means you can subtract fiber and sugar alcohols (like xylitol) out of your daily carb count — they don’t affect your blood sugar or get stored as glycogen, the storage form of glucose.



  • Standard keto: Standard keto dieters eat very low carb (less than 50 grams of net carbs a day), every day. Some keto followers eat as few as 20 grams per day. 
  • Cyclical keto: People who follow a cyclical keto diet eat a high-fat, low-carb (less than 50 grams of net carbs per day) five to six days a week. On day seven, they will have a carb refeed day (approximately 150 grams of net carbs). The Bulletproof Diet falls into this category, but tweaks keto for even better performance with intermittent fasting, protein fasting and an emphasis on nutrient-dense, low-inflammation foods.
  • Targeted keto: You follow the standard keto diet, but eat extra carbs 30 minutes to an hour before a high-intensity workout. The glucose is meant to boost performance, and you return to ketosis after the workout. If your energy is suffering in the gym during keto, this style of eating might work for you. 
  • Dirty keto: Dirty keto follows the same ratio of fats, proteins and carbs as the regular keto diet, but with a twist: It doesn’t matter where those macronutrients come from. Dinner could be a bunless Big Mac with a Diet Pepsi. Learn more about the dirty keto diet and how it works. 
  • Moderate keto: Eat high fat with 100-150 grams of net carbs every day. Women who experience problems with other forms of keto sometimes do better with this diet — restricting carbs can sometimes mess with hormonal function. Also, some athletes find they burn out with fewer than 100 grams of carbs on workout days.

When your body burns its stores of fat, it can be hard on your kidneys. And starting a ketogenic diet — or going back to a normal diet afterward — can be tricky if you’re obese because of other health issues you’re likely to have, like diabetes, a heart condition, or high blood pressure. If you have any of these conditions, make diet changes slowly and only with the guidance of your doctor.

The Complete Guide to a High Fat Diet, with More Than 125 Delectable Recipes and 5 Meal Plans to Shed Weight, Heal Your Body, and Regain Confidence. 

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