🥗 Nutrition
Keto Diet for Beginners — Complete Guide to Getting Started (2026)
Everything you need to start the ketogenic diet safely. What to eat, what to avoid, how long to see results, and who should avoid keto. Updated January 2026.
Key Takeaways
- Ketogenic diet: under 50g carbs per day, approximately 70–75% fat, 20–25% protein
- Most people reach ketosis within 2–4 days of reducing carbs below 50g daily
- The 'keto flu' — fatigue, headaches, irritability in week 1 — affects most beginners and resolves in 1–2 weeks
- Keto produces more weight loss than low-fat diets in the first 6 months — results equalise at 12 months
- Type 2 diabetics on medication must monitor blood sugar closely — keto can cause hypoglycaemia
In This Article
What Is the Ketogenic Diet?
The ketogenic (keto) diet is a very low-carbohydrate, high-fat dietary pattern that shifts the body's primary fuel source from glucose to ketone bodies — produced by the liver from dietary fat and stored body fat. This metabolic state is called nutritional ketosis.
| Macronutrient | Standard Diet | Ketogenic Diet |
|---|---|---|
| Carbohydrates | 45–65% | 5–10% (under 50g) |
| Fat | 20–35% | 70–75% |
| Protein | 10–35% | 20–25% |
2–4 days
Time to reach ketosis after reducing carbs below 50g
2–5 kg
Typical water weight loss in first week
1–2 wks
Duration of keto flu in most beginners
Foods to Eat on Keto
Eat Freely
- Fats: Butter, ghee, coconut oil, extra virgin olive oil, avocado oil
- Protein: Eggs, fatty fish (salmon, sardines), beef, pork, chicken (with skin), lamb
- Dairy: Hard cheese, cream, full-fat yoghurt (small amounts), cream cheese
- Low-carb vegetables: Spinach, kale, broccoli, cauliflower, courgette, cucumber, peppers
- Nuts/seeds: Macadamia, almonds, walnuts, pecans, chia, flaxseed
Avoid Completely
- All bread, pasta, rice, potatoes, cereals
- Fruit (except small amounts of berries)
- Sugary drinks, alcohol (most types)
- Most dairy (milk, ice cream)
- Beans and legumes (too high in carbs)
The Keto Flu — What to Expect
In the first 3–10 days, most people experience what is called the 'keto flu': headaches, fatigue, brain fog, irritability, and muscle cramps. This is caused by:
- Depletion of glycogen stores and associated water loss (2–4 kg weight drop)
- Electrolyte imbalance — sodium, potassium, and magnesium are lost with water
- The brain transitioning from glucose to ketone fuel
Solution: Drink 2–3 litres of water daily. Add salt to food. Take magnesium glycinate 300mg and potassium from food (avocado, spinach, nuts). Symptoms typically resolve within 1–2 weeks.
⚠️ Who Should NOT Try Keto Without Medical Supervision
People with Type 1 diabetes (risk of diabetic ketoacidosis) · People with kidney disease (high protein load) · People on insulin or sulphonylureas (hypoglycaemia risk) · People with liver disease · People with gallbladder disease (high fat triggers attacks) · Pregnant or breastfeeding women. Always consult your GP before starting any restrictive dietary pattern if you have existing health conditions.Frequently Asked Questions
How do I know if I am in ketosis?▼
The most reliable way is testing blood ketones with a ketone meter (target: 0.5–3.0 mmol/L for nutritional ketosis). Urine ketone strips are less accurate as urine ketone levels drop as the body adapts. Signs of ketosis: reduced appetite, mental clarity ('keto clarity'), acetone breath (fruity smell), and initial rapid weight loss from water and glycogen loss.
How long does it take to lose weight on keto?▼
Most people lose 2–5 kg in the first week — primarily water and glycogen (not fat). True fat loss begins in week 2–3. After 3 months, fat loss averages 0.5–1 kg/week with a maintained calorie deficit. Long-term (12 months), keto and other dietary approaches produce similar total weight loss when calorie intake is equal.
Can I exercise on a keto diet?▼
Yes — but performance may be impaired in the first 2–4 weeks as the body adapts to using fat and ketones for fuel. High-intensity exercise (sprinting, heavy weight training) may initially suffer more than low-intensity aerobic exercise. After 4–6 weeks of fat adaptation, most people find their performance returns to normal or improves for endurance activities.
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⚕️ Medical Disclaimer: For informational purposes only. Not a substitute for professional medical advice.
EC
Dr. Emma Clarke, PhD, RD
WellCalc Medical Contributor
All articles reviewed by qualified healthcare professionals following NHS, AHA, and WHO guidelines.