What is the keto diet? A plain-English beginner's guide
9 min read · Reviewed October 18, 2026 · By the KetoSwap team
How the ketogenic diet works, how many carbs you can eat, what to eat and avoid, and how to start safely.
The ketogenic ("keto") diet is a very-low-carbohydrate way of eating. By cutting carbs to roughly 20–50 grams a day and eating mostly fat, protein and non-starchy vegetables, you shift your body from running mainly on glucose to running mainly on fat and ketones. Here's how it works, what to eat, and how to start without feeling awful.
How keto works
Normally your body burns glucose from carbohydrates for quick energy. When carbs become scarce, insulin levels fall and your liver starts converting fatty acids into ketone bodies — beta-hydroxybutyrate, acetoacetate and acetone. Your brain, heart and muscles can use these ketones as fuel. That metabolic state is called nutritional ketosis.
The diet was developed in the 1920s to treat epilepsy, and is still used medically for drug-resistant seizures. Today most people use it for weight loss, appetite control or blood-sugar management.
How many carbs can you eat on keto?
Most people stay in ketosis below about 20–50 g of net carbs a day. Starting at 20–25 g makes it very likely you'll get there; once adapted, some people can go higher. Net carbs are total carbohydrates minus fiber — read our net carbs guide to learn how to count them from a label.
To put 20 g in perspective: one medium baked potato has about 33 g net carbs and a cup of cooked white rice about 44 g, while a cup of broccoli has about 3.7 g. Keto doesn't remove vegetables — it removes starch and sugar.
Keto macros
A typical keto day gets its calories roughly like this:
| Macro | Share of calories | Typical amount |
|---|---|---|
| Fat | 60–75% | Whatever keeps you satisfied within your calorie needs |
| Protein | 20–30% | About 1.2–2.0 g per kg of lean body mass |
| Net carbs | 5–10% | 20–50 g per day |
Protein is not the enemy on keto — getting enough protects muscle and keeps you full. Get personalized targets with our keto macro calculator.
What to eat on keto
- Meat, poultry and seafood: beef, pork, chicken, lamb, salmon, shrimp — all zero or near-zero carb.
- Eggs and full-fat dairy: eggs, butter, cream, cheese, sour cream, cream cheese.
- Non-starchy vegetables: leafy greens, broccoli, cauliflower, zucchini, peppers, mushrooms, asparagus, cabbage.
- Healthy fats: olive oil, avocado, avocado oil, coconut oil, nuts and seeds in measured portions.
- Some fruit: berries in small portions, plus avocado, olives, lemon and lime.
Eggs Keto 
Ground beef (80/20) Keto 
Salmon Keto 
Cheddar cheese Keto 
Avocado Keto 
Broccoli Keto 
Spinach Keto 
Olive oil Keto What to avoid
- Grains and starches: bread, pasta, rice, oats, cereal, crackers, tortillas.
- Sugar in all forms: table sugar, honey, maple syrup, agave, soda, juice, candy and most desserts.
- Starchy vegetables: potatoes, sweet potatoes, corn, peas, parsnips.
- Most fruit: bananas, apples, grapes, mango, pineapple and dried fruit.
- Beans and lentils (except black soybeans and modest edamame).
- Sweet sauces: ketchup, BBQ sauce, teriyaki and honey mustard.
White bread Not keto 
White rice Not keto 
Pasta Not keto 
Potatoes Not keto 
Bananas Not keto 
Soda (regular) Not keto 
Sugar Not keto 
Black beans Not keto Miss them? Our swap guides show the best low-carb replacements for each.
How to start keto in 7 steps
- Clear the obvious carbs. Bread, pasta, rice, cereal, chips, sweets and sugary drinks.
- Stock up on staples. Use our printable keto shopping list.
- Plan your first week. Follow our 7-day keto meal plan so you don't have to think.
- Learn three swaps. Cauliflower rice, cauliflower mash and zucchini noodles cover most dinners.
- Salt your food and drink water. This prevents most "keto flu" symptoms.
- Read labels. Sugar hides in sauces, dressings and processed meats — see hidden carbs.
- Give it two to four weeks. The first week is the hardest; energy usually rebounds as you adapt.
Possible side effects
The most common is the "keto flu" — headache, fatigue and irritability in the first week, mostly caused by sodium and fluid loss. Others include constipation (eat plenty of low-carb vegetables and drink water), temporary dips in exercise performance, bad breath from acetone, and changes in cholesterol. Some people see LDL cholesterol rise, so it's worth checking your lipids with your doctor after a few months.
Who should be careful
Talk to a healthcare professional before starting keto if you:
- Take medication for diabetes (especially insulin, sulfonylureas or SGLT2 inhibitors) or for blood pressure — doses often need adjusting quickly.
- Are pregnant or breastfeeding.
- Have kidney, liver, gallbladder or pancreatic disease, or a rare disorder of fat metabolism.
- Have a history of disordered eating.
Frequently asked questions
How long does it take to get into ketosis?
Most people reach nutritional ketosis within 2–4 days of eating fewer than about 20–50 g of carbs a day. Full adaptation — when energy and exercise performance return to normal — usually takes a few weeks.
Is ketosis the same as ketoacidosis?
No. Nutritional ketosis produces modest ketone levels (roughly 0.5–3 mmol/L in blood). Diabetic ketoacidosis is a dangerous state with very high ketones and high blood sugar, mainly in people with type 1 diabetes or insulin deficiency. People with diabetes should only try keto under medical supervision.
Can I eat fruit on keto?
Small portions of berries (raspberries, blackberries, strawberries) fit, as do avocado, olives, lemons and limes. Most other fruit is too sugary. See our keto fruit list.
Do I need to count calories on keto?
Many people lose weight without counting because protein and fat are filling. If progress stalls, tracking calories for a few weeks with our macro calculator can help.
This guide is general information, not medical advice. Talk to your doctor before starting keto — especially if you take medication for diabetes or blood pressure, are pregnant or breastfeeding, or have kidney, liver or gallbladder disease.