A ketogenic diet is a high-fat, very low-carbohydrate eating pattern that typically draws 70 to 80% of daily calories from fat, 10 to 20% from protein, and just 5 to 10% from carbohydrates. For most people, that carbohydrate range translates to roughly 20 to 50 grams per day, which is enough to fill a small side salad but far less than the average diet provides. The goal is to shift your body into a metabolic state called ketosis, where it burns fat for fuel instead of glucose.
How Ketosis Works
When you drastically cut carbohydrates, your blood sugar and insulin levels drop. Your body’s preferred fuel source, glucose, becomes scarce. In response, your liver begins breaking down stored and dietary fat into molecules it can convert into ketone bodies. These ketones circulate through your bloodstream and become the primary energy source for your brain, muscles, and other organs.
This switch doesn’t happen immediately. It generally takes two to four days of eating fewer than 50 grams of carbohydrates for the liver to ramp up ketone production. The transition period is when most people notice the biggest shift in how they feel, including some uncomfortable side effects (more on that below).
What You Eat on Keto
Because fat accounts for the vast majority of your calories, every meal revolves around fat-rich foods. The protein portion is moderate, not high, and carbohydrates come almost exclusively from non-starchy vegetables and small amounts of other whole foods.
Fats
The backbone of keto meals includes oils (olive, coconut, avocado), butter, ghee, nuts and nut butters, seeds, avocados, cheese, and fatty cuts of meat or fish. Full-fat dairy like heavy cream and sour cream also fits. Many people cook with coconut oil or butter and add olive oil to salads to hit their fat targets. The quality of fat matters for overall health: prioritizing sources like olive oil, fatty fish, nuts, and avocados over processed fats is a common recommendation.
Protein
Protein sources include eggs, poultry, beef, pork, lamb, fish, shellfish, and full-fat dairy. Protein is kept moderate rather than high for a specific reason: your liver can convert amino acids from protein into glucose through a process called gluconeogenesis. If you eat significantly more protein than you need, your body may use those amino acids to produce glucose, which can interfere with maintaining ketosis. The practical takeaway is that keto is not a steak-at-every-meal diet. Portions of protein are intentional, typically around a palm-sized serving at each meal.
Low-Carb Vegetables
Non-starchy vegetables are the primary source of fiber, vitamins, and minerals on keto. Leafy greens like spinach, kale, and lettuce are extremely low in carbohydrates. Other staples include broccoli, cauliflower, zucchini, bell peppers, asparagus, mushrooms, and cucumber. Cauliflower plays a particularly popular role as a stand-in for high-carb foods: mashed cauliflower replaces mashed potatoes, and riced cauliflower substitutes for rice or couscous. Spaghetti squash serves as a pasta alternative, and jicama or turnips can replace roasted potatoes.
What You Avoid
The restricted list is essentially everything carbohydrate-dense. That means all grains and grain-based foods: bread, pasta, rice, oats, cereal, tortillas, and baked goods. Sugar in all its forms is out, including table sugar, honey, maple syrup, agave, candy, and most desserts. Starchy vegetables like potatoes, sweet potatoes, corn, and peas are too carb-heavy. Most fruits are also excluded because of their natural sugar content, especially bananas, apples, oranges, grapes, and mangoes. Small portions of berries (strawberries, blueberries, raspberries) are the main exception, as they’re lower in sugar.
Legumes like beans, lentils, and chickpeas are typically avoided. Sugary beverages, juice, beer, and sweetened condiments like ketchup and barbecue sauce are also common pitfalls that can push you over your daily carb limit without you realizing it.
Keto-Friendly Drinks
Water is the obvious foundation, but the full list of zero- or near-zero-carb drinks is longer than many people expect. Black coffee (0 to 1 gram of carbs per cup) and unsweetened tea, including green, black, oolong, and herbal varieties, all fit easily. You can add a splash of heavy cream or unsweetened almond milk to coffee without issue. Sparkling water works as long as it has no added sugar or juice. Unsweetened almond milk runs about 1 gram of net carbs per cup, and unsweetened coconut milk is 1 to 2 grams.
Bone broth (0 to 2 grams per cup) is a popular option, partly because it provides sodium and other electrolytes. For alcohol, dry wine and plain spirits like vodka or gin mixed with soda water are the lowest-carb choices. Sweet cocktails, regular beer, and dessert wines are high enough in carbs to knock you out of ketosis.
The “Keto Flu” Transition
During the first week, many people experience a cluster of symptoms commonly called keto flu. The most frequently reported issues are headache, fatigue, nausea, dizziness, brain fog, gastrointestinal discomfort, low energy, feeling faint, and changes in heartbeat. These symptoms typically peak within the first week and gradually fade over the first month. A study examining consumer reports found that most people experienced resolution between day 3 and day 30, with a median of about 4.5 days.
The leading explanation is a rapid loss of water and electrolytes. When carbohydrate stores deplete, your body releases a significant amount of water, and sodium, potassium, and magnesium go with it. The most common remedies people use are increasing sodium intake (adding salt to food or drinking broth), supplementing magnesium, and increasing potassium through foods like avocado and leafy greens or supplements. Staying well-hydrated through this adjustment period is important.
Why Protein Stays Moderate
This is one of the most misunderstood parts of keto. Many people assume that if carbs are low, they should just eat unlimited meat and eggs. But the body can convert certain amino acids into glucose when carbohydrate availability is low. This process happens primarily in the liver, using amino acids like alanine and glutamine as raw material. If protein intake is high enough to significantly boost glucose production, it can raise blood sugar and insulin just enough to reduce ketone levels and pull you out of ketosis.
There’s also a concern about muscle tissue. When carbohydrates are severely restricted, the body may break down some muscle protein to supply amino acids for glucose production. Eating adequate (but not excessive) protein helps protect against this while keeping ketone levels stable. Most keto guidelines place protein at 10 to 20% of total calories, which for a 2,000-calorie diet works out to roughly 50 to 100 grams per day.
What the Evidence Shows About Safety
Short-term studies consistently show improvements in weight, blood sugar control, and certain metabolic markers. However, most clinical trials on the ketogenic diet last less than a year, and long-term safety data remains limited. Reported complications in longer-term or clinical use include unfavorable changes in cholesterol levels, kidney stones, reduced bone mineral density, and, in children, potential growth impairment. Epilepsy remains the only condition for which the ketogenic diet has formal, guideline-supported medical backing. Applications in obesity, diabetes, liver disease, and neurological conditions are still considered investigational by major medical organizations.
The diet is contraindicated for people with pancreatitis, liver failure, certain fat-metabolism disorders, and porphyrias. It is not recommended during pregnancy due to potential effects on fetal development. People with a history of eating disorders should avoid it, as the rigid rules and rapid body changes can trigger relapse. Anyone taking certain diabetes medications, particularly SGLT2 inhibitors, faces a substantially higher risk of a dangerous form of diabetic ketoacidosis on a ketogenic diet.