Keto Diet: Complete Guide
Last updated: 20 February 2026
The keto diet (ketogenic diet) is a very low-carb, high-fat, moderate-protein eating pattern that aims to put your body into ketosis–a state where it burns fat and uses ketones for energy instead of glucose from carbohydrates. It is popular for weight loss and is also used under medical supervision for epilepsy. Many people use a keto diet for beginners approach or a simple keto diet meal plan to get started. This guide explains what the keto diet is, how it works, what to eat and avoid, potential benefits and side effects, and who should be cautious. It is based on current clinical and scientific sources; always discuss any diet change with your doctor or dietitian, especially if you have a health condition or take medication.
Disclaimer: This page is for education only and does not replace advice from your doctor or dietitian. The keto diet is not safe for everyone. Before starting, especially if you have diabetes, kidney or liver disease, or an eating disorder, speak to a healthcare professional.
Below you will find a clear definition of the keto diet, how ketosis works, a keto diet food list and foods to avoid, benefits and risks, a sample day of meals, and answers to common questions. You can use our calorie calculator and TDEE calculator to understand your energy needs if you combine keto with a weight goal.
What is the keto diet?
The keto diet (short for ketogenic diet) is an eating pattern that severely restricts carbohydrates and emphasises fat, with moderate protein. Typically, carbs are limited to around 20–50 grams per day (about 5–10% of calories), fat provides about 70–80% of calories, and protein about 10–20%. The goal is to shift the body into ketosis: when carbohydrate intake is very low, the liver produces ketones from fat, and the brain and other tissues use these ketones for fuel instead of glucose.
The therapeutic ketogenic diet was developed in the 1920s for epilepsy and is still used in medical settings for certain seizure disorders. The modern “keto diet” for weight loss and general health uses similar macronutrient ratios but is not the same as medically supervised ketogenic therapy. Variations include lazy keto (only tracking carbs), high protein keto (more protein, slightly more carbs), vegan keto and vegetarian keto (plant-based fats and proteins only), and cyclical keto (keto cycle diet with higher-carb days).
Core principles
- Keep total carbohydrates very low (often under 20–50 g net carbs per day).
- Eat enough fat so that it becomes the main energy source.
- Moderate protein–enough to preserve muscle, not so high that it blocks ketosis.
- Focus on whole or minimally processed keto diet foods: meat, fish, eggs, full-fat dairy, non-starchy vegetables, nuts, seeds, and healthy oils.
How the keto diet works
When you eat very few carbs, your body’s supply of glucose (from carbs) drops. After a few days, the liver starts breaking down fat into ketones (e.g. beta-hydroxybutyrate). Once ketone levels rise, your body is in ketosis. In this state, fat and ketones supply most of your energy. This is the mechanism behind the keto diet for weight loss: you restrict a major calorie source (carbs) and may feel less hungry, which can help you eat in a calorie deficit. Weight loss itself still requires burning more calories than you consume; keto is one way to get there.
There are no mandatory “phases” in a basic keto diet–you adopt the macros and maintain them. Some plans (e.g. Atkins) start very low carb and later add more carbs; that is a different structure. For a straightforward easy keto diet plan or keto diet plan for beginners, the first step is learning the keto diet food list and foods to avoid, then building a simple keto diet menu. A free keto diet plan or keto diet meal plan free from a reputable source can give you a template; you can also use a keto diet app to track carbs and stay within your targets.
What to eat and what to avoid on the keto diet
A keto diet food list centres on foods that are low in carbs and high in fat (or moderate in protein). The table below summarises the best foods for keto diet and keto diet foods to avoid.
| Eat (keto diet foods) | Eat in moderation | Avoid or limit (foods to avoid on keto diet) |
|---|---|---|
| Meat (beef, pork, lamb, poultry) | Full-fat cheese | Bread, pasta, rice, grains |
| Fish and seafood | Nuts (best nuts for keto: almonds, macadamia, pecans–watch portions) | Sugar, honey, syrup, sweets |
| Eggs | Berries (small amounts) | Most fruits (high carb) |
| Non-starchy vegetables (leafy greens, broccoli, cauliflower, zucchini, peppers) | Dark chocolate (high cocoa, small portions) | Potatoes, corn, peas, most legumes |
| Avocado, olives | Keto diet snacks (e.g. cheese, nuts, olives) | Beer, sugary drinks, most milk (lactose) |
| Olive oil, avocado oil, butter, coconut oil | Heavy cream, full-fat yogurt (plain) | Processed low-fat “diet” foods (often high in carbs) |
When planning keto diet meals, base each meal on a protein source (meat, fish, eggs), add low-carb vegetables and a source of fat (oil, butter, avocado). For a keto diet shopping list, focus on the “eat” column and check labels for hidden carbs. Ketogenic diet foods and ketogenic diet food list resources from hospitals or dietitian sites often list exact carb counts. If you follow a vegetarian keto diet or vegan keto diet, you rely on eggs and dairy (vegetarian) or tofu, tempeh, nuts, seeds, avocado, and low-carb vegetables (vegan keto diet plan); it is more restrictive but doable with planning.
Potential benefits of the keto diet
Evidence varies by outcome. Benefits are often described as “may” or “in some studies”–not guaranteed for everyone.
- Weight loss: Short-term trials show that a keto diet for weight loss or ketogenic diet for weight loss can lead to weight loss, partly due to reduced appetite and lower calorie intake. Long-term comparison with other diets is mixed; adherence matters more than the diet name. A keto diet plan for weight loss should still align with your TDEE and calorie goals.
- Blood sugar and diabetes: Some research suggests the keto diet for diabetics / keto diet and diabetes may improve blood sugar and insulin sensitivity in type 2 diabetes. However, it can change medication needs (e.g. less insulin) and carries risks–it must be done only under medical supervision.
- Epilepsy: The keto diet for epilepsy (therapeutic ketogenic diet) has strong evidence in children and some adults with drug-resistant epilepsy. This is always managed by a medical team, not a DIY plan.
- Other: Interest exists in keto for PCOS, neurological conditions, and metabolic health; evidence is still evolving. A healthy keto diet emphasises whole foods and quality fats rather than processed “keto” products.
Quality of evidence: weight loss and metabolic outcomes are supported by short-term trials; long-term data and comparisons with other diets are limited. For epilepsy, the ketogenic diet is well established in clinical guidelines. Always discuss with your doctor whether keto is appropriate for you.
Risks and who should avoid or be cautious
Keto diet side effects are common, especially at the start. Many people experience “keto flu”: headache, fatigue, brain fog, irritability, and sometimes nausea or dizziness as the body adapts. These usually improve within a few days to a week. Other possible effects include constipation (from low fibre), bad breath (acetone from ketones), muscle cramps (electrolyte shifts), and nutrient gaps (e.g. fibre, some vitamins) if the diet is not well planned.
The keto diet is not suitable for everyone. It is generally not recommended for:
- Pregnant or breastfeeding women (unless under strict medical guidance).
- People with certain kidney, liver, or pancreatic conditions.
- People with a history of eating disorders.
- Those on medications that are affected by diet (e.g. diabetes drugs)–any change must be supervised by a doctor.
Long-term safety of a very high-fat, very low-carb diet in the general population is still debated. Before starting a keto diet, especially for weight loss or diabetes, consult your doctor or a registered dietitian. They can help you decide if it is appropriate and how to minimise risks.
Sample keto diet day (meal ideas)
This is one example of a keto diet menu or ketogenic diet menu–not a prescriptive keto diet plan. Adjust portions and foods to your calorie needs and preferences.
- Breakfast: Scrambled eggs with spinach and cheese; or full-fat Greek yogurt (plain) with a few berries and nuts; or an omelette with avocado (simple keto diet meals for beginners).
- Lunch: Salad with grilled chicken, olive oil, avocado, and leafy greens; or salmon with asparagus and butter; or lettuce wraps with tuna and mayo.
- Dinner: Steak or pork chops with cauliflower mash and broccoli; or baked fish with zucchini and olive oil; or chicken thighs with a side of sautéed greens.
- Keto diet snacks: Cheese, olives, nuts (e.g. almonds, macadamia), celery with nut butter, hard-boiled eggs, or a small portion of berries.
For more structure, use a keto diet meal plan or easy keto diet plan from a reputable source or dietitian. Many sites offer keto diet recipes for breakfast, lunch, and dinner; a keto diet list or keto diet shopping list can help you stock the right ketogenic diet foods. A diet doctor keto style plan or similar can provide a clear framework.
Frequently asked questions about the keto diet
The keto (ketogenic) diet is a very low-carb, high-fat, moderate-protein eating pattern. It aims to put the body into ketosis, where it burns fat and produces ketones for energy instead of relying on glucose from carbohydrates. It is used for weight loss and, in medical settings, for epilepsy.
You focus on meat, fish, eggs, full-fat dairy, non-starchy vegetables, nuts, seeds, and healthy oils (e.g. olive, avocado). You avoid or minimise grains, bread, pasta, sugar, most fruits, starchy vegetables, and legumes. A keto diet food list typically includes leafy greens, avocado, cheese, and fatty fish. Check the “What to eat and what to avoid” section above for a full list.
Short-term studies show that the keto diet can support weight loss, partly because it restricts carbs and may reduce appetite. Weight loss still depends on eating in a calorie deficit. For personalised targets, use a calorie calculator or TDEE calculator and discuss with a dietitian.
Common side effects when starting include headache, fatigue, brain fog, and digestive issues (constipation or diarrhoea)–often called “keto flu.” Some people experience bad breath, muscle cramps, or nutrient gaps. Not everyone should do keto; people with certain kidney, liver, or metabolic conditions should avoid it unless under medical supervision. See the “Risks” section above for more.
Some research suggests a ketogenic diet may help with blood sugar and insulin in type 2 diabetes, but it can also affect medication needs (e.g. insulin) and carries risks. It should only be tried under medical supervision. Never change diabetes medication or diet without your doctor’s guidance.
Lazy keto means focusing only on keeping carbs very low (e.g. under 20–50 g per day) without tracking fat and protein precisely. It is simpler but may not produce the same level of ketosis as strict keto. It can work for some people for weight loss but is not suitable for medical keto (e.g. epilepsy).
Summary
The keto diet is a very low-carb, high-fat eating pattern that can put the body into ketosis and is used for weight loss and, under medical care, for epilepsy. It emphasises keto diet foods such as meat, fish, eggs, non-starchy vegetables, nuts, and healthy oils, and avoids grains, sugar, and most fruits. Benefits may include short-term weight loss and, in some studies, better blood sugar control; side effects include “keto flu” and possible nutrient gaps. It is not safe for everyone–pregnant women, people with certain kidney or liver conditions, and those on diabetes medication should only consider it with a doctor. Before starting, talk to your doctor or a dietitian and use our calorie calculator and TDEE calculator if you have a weight goal. For other approaches, see our guides to the low-carb diet, Mediterranean diet, or DASH diet.
Use our calculators with this diet
Set your calorie target and plan meals with our free tools.
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Other diet guides that may fit your goals.
Low-carb diet
Fewer carbs, more protein and fat. Used for weight loss and blood sugar.
Atkins diet
Phased low-carb plan. Starts very low carb, then adds carbs back.
Weight loss diet
Balanced eating with a calorie deficit for sustainable weight loss.
Diabetic diet
Carb awareness and balanced meals to support blood sugar control.
Sources and further reading
This article is based on current scientific and clinical sources. For more detail, see:
- NIH / NIDDK: Weight management and dietary approaches
- Mayo Clinic: Ketogenic diet – what you need to know
- American Diabetes Association: Low-carb and ketogenic diets in type 2 diabetes (position statements)
- Epilepsy Foundation and clinical guidelines on ketogenic diet for epilepsy
- Cochrane and systematic reviews on ketogenic diet for weight loss and metabolic outcomes
Last updated: 20 February 2026. Content is for educational purposes only and does not replace medical advice.