What is the keto diet? A doctor's plain-language explanation

The ketogenic diet is a very-low-carbohydrate way of eating in which the body switches from burning carbs to burning fat. Here is what actually happens in the body, who it fits and who should avoid it.

What happens in the body

When carbohydrate intake drops below ~20–50 g/day, liver glycogen is depleted in 24–48 hours. The liver then produces ketone bodies (β-hydroxybutyrate, acetoacetate) from fatty acids, which become alternative fuel for brain and muscle. This nutritional ketosis is fundamentally different from diabetic ketoacidosis, which is dangerous and occurs only in insulin deficiency.

Three keto variants

• Standard keto (SKD): 70–75% fat, 20% protein, 5–10% carbs
• High-protein keto: 60% fat, 35% protein, 5% carbs — for people who train
• Cyclical keto: 5–6 strict days + 1–2 carb days — for athletes

Evidence base

A meta-analysis (Bueno et al., Br J Nutr 2013) showed greater 12-month weight loss on keto vs low-fat. The Virta Health trial (Hallberg 2018) reported 60% one-year remission of type-2 diabetes. In epilepsy, keto has been a clinical standard since the 1920s.

Who should NOT do keto

• Pregnancy and lactation (unless medically supervised)
• Type-1 diabetes without frequent glucose monitoring
• Renal or hepatic failure
• History of eating disorders
• Rare inherited fatty-acid oxidation defects

How to start correctly

Start with 2–4 strict weeks (< 20 g net carbs) to allow adaptation. Drink 2.5–3 L water, add 3–5 g extra sodium and 300–400 mg magnesium — this prevents "keto flu". Eat food, not products: meat, fish, eggs, avocado, olive oil, nuts, leafy greens.