A keto-friendly diet is a high-fat, very low-carbohydrate eating pattern designed to shift your body’s primary fuel source from glucose to fat. The typical breakdown is 70 to 80% of daily calories from fat, 10 to 20% from protein, and only 5 to 10% from carbohydrates. In practical terms, that means keeping your carb intake to roughly 20 to 40 grams per day, which is less than what you’d find in a single bagel.
How Ketosis Works in Your Body
Under normal conditions, your body runs on glucose from carbohydrates. When you drastically cut carbs, your insulin levels drop. That drop signals your fat tissue to start releasing stored fat into the bloodstream as free fatty acids. Your liver picks up those fatty acids and begins breaking them down for energy.
Here’s where the chemistry gets interesting. As the liver breaks down all that fat, it produces a molecule called acetyl-CoA faster than it can burn it through its normal energy cycle. The backup happens because a key ingredient in that cycle, oxaloacetate, gets redirected to make small amounts of glucose for tissues that absolutely require it, like red blood cells. With nowhere else to go, the excess acetyl-CoA gets converted into ketone bodies, which are released into your bloodstream and used as fuel by your muscles, heart, and, critically, your brain. This metabolic state is called ketosis, and it’s the entire goal of the diet.
What to Eat on Keto
Building meals around high-fat, low-carb whole foods is the foundation. The categories are straightforward:
- Meat and poultry: Chicken, beef, pork, and fish contain zero carbohydrates and provide B vitamins, potassium, selenium, and zinc.
- Cheese: Most cheeses have zero carbs and are naturally high in fat. A one-ounce slice of cheddar has about 5 grams of saturated fat, so mixing in softer cheeses or those with more favorable fat profiles helps balance things out.
- Low-carb vegetables: Aim for nonstarchy options with fewer than 8 grams of net carbs per cup. Broccoli, cauliflower, green beans, bell peppers, zucchini, and spinach all qualify.
- Avocados: Half a medium avocado has about 6 grams of total carbs, but 4.5 of those are fiber, leaving just 1.5 grams of net carbs. It also delivers 360 milligrams of potassium.
- Fats and oils: Olive oil, coconut oil, butter, and nuts form the calorie backbone of most keto meals.
- Eggs: Virtually zero carbs with a good balance of fat and protein.
Foods That Will Knock You Out of Ketosis
Staying under 20 to 40 grams of carbs per day means most of the foods in a standard diet are off the table. Bread, pasta, rice, cereal, and other grains are the most obvious cuts. Most fruits are too high in sugar, with bananas, grapes, and mangoes being particularly carb-dense. Starchy vegetables like potatoes, corn, and peas are also out.
The trickier culprits are hidden sugars. Sauces like ketchup, barbecue sauce, and teriyaki can pack 5 to 10 grams of carbs per tablespoon. Flavored yogurts, granola bars, and many “health” drinks are loaded with added sugar. Even beans and legumes, despite being high in fiber, carry enough total carbohydrate to use up most of a day’s allowance in a single serving.
How to Count Net Carbs
Most people following keto track “net carbs” rather than total carbs. The formula is simple: total carbohydrates minus fiber minus sugar alcohols. Fiber and sugar alcohols get subtracted because they don’t significantly raise blood sugar. So a food with 24 grams of total carbs, 10 grams of fiber, and 8 grams of sugar alcohols would have just 6 net carbs. This is how many keto-labeled products on store shelves advertise surprisingly low carb counts.
Health Benefits With Strong Evidence
The ketogenic diet was originally developed in the 1920s as a treatment for epilepsy in children who didn’t respond to medication. That remains its best-supported medical use. In drug-resistant epilepsy, the diet consistently reduces seizure frequency and severity across both children and adults, and it’s a standard treatment for two rare metabolic conditions: glucose transporter type 1 deficiency and pyruvate dehydrogenase deficiency.
For weight loss and type 2 diabetes, the evidence is also positive, though less dramatic. Multiple randomized controlled trials show the diet leads to reductions in body weight, triglycerides, fasting blood sugar, and blood pressure compared to low-fat diets. It also tends to raise HDL (“good”) cholesterol and improve insulin sensitivity. A randomized crossover trial in people with type 2 diabetes found significant weight loss and better blood sugar control, though the improvement in long-term blood sugar markers was modest, and many participants struggled to stick with the diet over time.
The “Keto Flu” and Electrolytes
During the first week or two, many people experience fatigue, headaches, irritability, nausea, and brain fog. This cluster of symptoms is commonly called the keto flu, and it’s largely caused by a rapid loss of water and electrolytes. When insulin drops, your kidneys start flushing sodium at a much higher rate, and potassium and magnesium follow.
Replacing those electrolytes intentionally makes a significant difference. The general targets for a well-formulated ketogenic diet are 3,000 to 5,000 milligrams of sodium per day, 3,000 to 4,000 milligrams of potassium, and 300 to 500 milligrams of magnesium. That sodium number is considerably higher than standard dietary advice, which is why many keto practitioners salt their food liberally or drink broth. Potassium comes from avocados, leafy greens, and mushrooms, while magnesium supplements or magnesium-rich foods like pumpkin seeds can cover the gap.
Checking Whether You’re in Ketosis
There are three ways to measure ketone levels: blood meters, breath analyzers, and urine strips. Blood testing is the most accurate. Nutritional ketosis begins at a blood concentration of 0.5 mmol/L or higher. Normal, non-ketotic levels sit below 0.5 mmol/L. Levels above 3.0 mmol/L enter the range associated with ketoacidosis, a dangerous condition that’s primarily a concern for people with type 1 diabetes rather than healthy individuals eating keto.
Urine strips are the cheapest option and work well early on, but they become less reliable over time as your body gets more efficient at using ketones instead of excreting them. Breath meters fall somewhere in between for accuracy and convenience.
Who Should Avoid Keto
The ketogenic diet is not safe for everyone. People with type 1 diabetes face a heightened risk of diabetic ketoacidosis, a life-threatening buildup of ketones combined with high blood sugar. Those taking SGLT-2 inhibitors (a common class of diabetes medication) are also at risk for a variant of ketoacidosis and should not combine these drugs with a ketogenic diet.
Pregnant and breastfeeding women should avoid keto entirely. Case reports suggest potential harm to fetal development, and lactation ketoacidosis, while rare, has been documented when a very low-carb diet is a contributing factor. People with advanced heart failure, a history of alcohol or substance abuse with risk of relapse, or certain rare metabolic disorders involving fat transport in cells cannot safely produce or process ketone bodies on this diet.
There is also preliminary evidence suggesting the diet could worsen outcomes in melanoma and kidney cancer, so people with those diagnoses are typically advised against it until more research is available.