A keto diet consists primarily of high-fat foods, moderate protein, and very few carbohydrates, typically 70 to 80% of daily calories from fat, 10 to 20% from protein, and only 5 to 10% from carbs. That carb limit usually works out to roughly 20 to 50 grams per day, which is dramatically less than the 200 to 300 grams most people eat. 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 cut carbohydrates low enough, your blood sugar and insulin levels drop. Without a steady supply of glucose, your liver begins breaking down fatty acids and converting them into molecules called ketone bodies. These ketones then circulate through your bloodstream and serve as fuel for your brain, muscles, and other organs. The liver is the only organ that can produce ketones this way.
This transition doesn’t happen overnight. It typically takes two to four days of very low carb eating before your body starts producing meaningful amounts of ketones. Nutritional ketosis is generally defined as having blood ketone levels between 0.5 and 3 mmol/L. Some people use urine strips or blood monitors to check, but most simply follow the carb limits and let the process happen naturally.
What You Eat on Keto
The bulk of your plate on a keto diet is fat. That includes avocados, olive oil, coconut oil, butter, cheese, nuts, and seeds. Fatty cuts of meat, salmon, sardines, and eggs are staples because they provide both fat and protein in good proportions. Full-fat dairy like heavy cream, sour cream, and cream cheese also fits well.
Protein sources stay moderate. Chicken thighs, beef, pork, lamb, and seafood all work, but the portion size matters. Eating too much protein can partially convert to glucose through a process in the liver, which some people find slows their progress. Most keto guidelines suggest keeping protein to about 10 to 20% of total calories.
Your carbohydrates come almost entirely from non-starchy vegetables: leafy greens like spinach and kale, broccoli, cauliflower, zucchini, bell peppers, asparagus, and mushrooms. These provide fiber, vitamins, and minerals while keeping your carb count low. Small amounts of berries (raspberries, blackberries, strawberries) are the most keto-friendly fruits, since most other fruits are too high in sugar.
Foods That Are Off the Table
The list of restricted foods is long because carbohydrates are everywhere. Bread, pasta, rice, cereal, and anything made with flour are the obvious ones. But plenty of foods surprise people. A single cup of canned baked beans has 54 grams of carbs, which could blow through an entire day’s allowance in one serving. Split pea soup packs about 26 grams per cup. Legumes, lentils, and most beans are too starchy to fit.
Fruits like bananas, apples, oranges, and grapes contain enough natural sugar to push you out of ketosis. Potatoes, corn, and sweet potatoes are out. So are sugary drinks, juice, beer, and most cocktails. Sauces, dressings, and marinades often contain hidden sugars. Even foods marketed as “healthy,” like granola, yogurt with fruit, and whole wheat bread, are too carb-heavy for keto.
The Adjustment Period
Most people feel noticeably worse before they feel better. A cluster of symptoms commonly called “keto flu” tends to appear two to seven days after starting the diet. Headache, fatigue, brain fog, irritability, nausea, difficulty sleeping, and constipation are the most common complaints. These symptoms reflect your body adjusting to a new fuel source, and for most people, energy levels return to normal within about a week.
Much of this discomfort comes from a shift in how your body handles water and minerals. When carb intake drops, your kidneys excrete more sodium, which pulls water and other electrolytes with it. A well-formulated keto diet requires significantly more sodium and potassium than most people realize: roughly 3,000 to 5,000 mg of sodium and 3,000 to 4,000 mg of potassium per day, plus 300 to 500 mg of magnesium. Salting food generously, drinking broth or bouillon, and eating at least five servings of non-starchy vegetables daily helps cover this gap. Muscle cramps are a reliable sign you’re falling short on magnesium.
A Typical Day of Eating
Breakfast might be eggs scrambled in butter with cheese and avocado, or a coffee blended with coconut oil. Lunch could be a salad with grilled chicken thighs, olive oil dressing, cheese, and sunflower seeds. Dinner often centers on a fatty protein like salmon or a ribeye steak alongside roasted broccoli or cauliflower cooked in butter. Snacks tend to be nuts, cheese, pork rinds, or celery with cream cheese.
The meals feel filling because fat is calorie-dense and slow to digest. Many people on keto report that they naturally eat less often because they stay satisfied longer between meals. This is one reason the diet can lead to weight loss even without deliberate calorie counting, though calories still matter overall.
Beyond Weight Loss
The ketogenic diet was originally developed as a medical treatment, not a weight-loss strategy. Johns Hopkins has used it to treat pediatric epilepsy since the 1920s, and it remains a standard therapy for children and adults whose seizures don’t respond well to medication. It’s also prescribed for a rare genetic condition called glucose transporter type 1 deficiency syndrome, where the brain can’t properly use glucose and needs ketones as an alternative fuel.
Research into the diet’s effects on type 2 diabetes, polycystic ovary syndrome, and neurological conditions is ongoing, but its strongest and longest clinical track record is in epilepsy management.
Keeping It Sustainable
The most common practical challenge with keto is fiber. Since you’re cutting out whole grains, most fruits, and legumes, your fiber intake can drop sharply, leading to constipation. Prioritizing high-fiber, low-carb vegetables like broccoli, Brussels sprouts, and leafy greens helps. Chia seeds, flaxseeds, and avocado are other good sources that fit within the macros.
Variety also takes effort. It’s easy to fall into a rotation of bacon, eggs, and cheese, but a keto diet built mainly around processed meats and saturated fat looks very different nutritionally from one centered on fish, olive oil, nuts, and vegetables. The quality of fats you choose matters as much as the quantity. Emphasizing monounsaturated and polyunsaturated fats from whole food sources gives you a more balanced nutrient profile over the long term.