The ketogenic diet: the complete guide to getting started

The ketogenic diet (or "keto") is probably the most talked-about way of eating of the last ten years: some describe it as a miracle solution, others dismiss it as a dangerous fad. As almost always, the truth sits in the middle — and it's far more interesting than the slogans.

This guide is the starting point: it lays out what ketosis is, what you eat, how to set calories and macros, what to expect in the first days and when keto is NOT a good idea. Each section points to the dedicated deep-dive: here you get the picture, there the details. No promises of "10 kg in a month".

Important note. This guide is for informative and educational purposes: it does not replace the advice of a doctor or nutritionist. If you have medical conditions, take medication or are pregnant, talk to a professional before changing your diet.

What the ketogenic diet is

The ketogenic diet is a way of eating that is very low in carbohydrates (usually under 20-50 g net per day), moderate in protein and rich in fat. As a percentage of calories, the classic reference is:

5-10% carbohydrates (versus 45-60% in a standard Mediterranean diet)
20-25% protein
70-75% fat

The drastic reduction in carbohydrates forces the body to switch fuel: once glycogen stores run out, the liver starts producing ketone bodies from fat, and most tissues — brain included — learn to use them as an energy source. This metabolic state is called nutritional ketosis: what it is exactly, what signs it gives and how to measure it is explained in Ketosis: what it is and how to tell if you're in it.

One misunderstanding to clear up straight away: nutritional ketosis (blood ketones typically between 0.5 and 3 mmol/L) has nothing to do with diabetic ketoacidosis, an acute and dangerous complication of diabetes in which ketones exceed those levels by 5-10 times in the absence of insulin. In a healthy person, hormonal regulation prevents dietary ketosis from degenerating into ketoacidosis.

Nor is it a recent invention: the ketogenic diet was born in the 1920s as a therapy for drug-resistant epilepsy, a field where it is still used today under medical supervision. Its popularity as a weight-loss tool came much later.

What to eat (and what to avoid)

Green light

Meat, fish and eggs: beef, pork, poultry; oily fish (mackerel, sardines), salmon. Fatty fish also bring omega-3s.
Above-ground vegetables: leafy greens, courgettes, broccoli, cauliflower, peppers, asparagus, mushrooms.
Quality fats: extra virgin olive oil, coconut oil, butter. Fatty fruit: avocado, olives, coconut.
Nuts and seeds (in moderation: the carbs add up) and full-fat dairy: aged cheeses, cream, whole Greek yogurt.
Berries: raspberries, blackberries, strawberries in moderate portions.

To avoid

Sugar in every form: sweets, soft drinks, juices, honey — but also the hidden sugars in sauces, fruit yogurts and "fitness" products.
Grains and derivatives (bread, pasta, rice, pizza, even wholegrain), potatoes and starchy tubers.
Legumes: chickpeas, beans, lentils (30-40 g of net carbs per 100 g dry).
Sugary fruit: bananas, grapes, figs, mango, persimmons.
"Low fat" products: they almost always make up for the removed fat with added sugar.

The most useful practical rule for shopping: real, minimally processed food — with the label as referee in doubtful cases. The complete list, category by category, is in What to eat and what to avoid; for the carbs in a specific food there's the carb and sugar calculator, and to pick vegetables month by month the seasonal calendar.

How many calories and macros: the numbers matter

"Eat as much fat as you want" is the worst advice out there. Ketosis improves hunger control — and that's one of its real advantages — but losing weight still requires a calorie deficit. Keto doesn't suspend thermodynamics: it makes it easier to stick to.

The correct setup starts from your energy needs (the Mifflin-St Jeor formula, the most accurate for the general population) and derives the three macros keto-style from there. The keto macro calculator does it all automatically: enter sex, age, weight, height, activity and goal, and you get the numbers to build your meals on.

Two numerical mistakes not to make:

Too little protein. It protects muscle mass while you lose weight and satiates more than any other macronutrient: a useful reference is 1.4-2 g per kg of body weight, as we explain in Protein: how much you need on keto.
Counting total carbs instead of net carbs. On keto, fibre is subtracted (it doesn't raise blood sugar): 100 g of broccoli has ~7 g of total carbs but only ~4 g net. Counting totals makes the diet needlessly restrictive.

How to start: the 7 steps

Do the maths before you start: calculate your macros with the calculator and write them down somewhere.
Empty the pantry of bread, pasta, snacks and soft drinks: willpower is overrated, your environment isn't.
Do a complete keto shop: eggs, meat, fish, above-ground vegetables, olive oil, nuts, cheeses. The recipes cover breakfast, lunch, dinner, snacks, desserts and even bread.
Plan the first 7 days of meals: the first week is when people give up; arriving with a plan halves the risk. The sample weekly menu is an already-balanced starting point.
Manage your electrolytes (see below): it's the step almost everyone skips and a frequent cause of the initial malaise.
Don't add other restrictions: no prolonged fasting or punishing workouts in the first two weeks. One change at a time.
Reassess after 30 days: weight, energy, blood tests if you do them routinely, and honesty about how sustainable the regime is for you.

The operational details of the first days — with the typical beginner mistakes — are in How to start the ketogenic diet and 5 mistakes to avoid when you start. For a guided article-by-article path there's the path.

The "keto flu", in a nutshell

In the first 3-7 days many people go through tiredness, headaches, irritability or cramps: the so-called keto flu. It's not "the body demanding sugar": it's largely a matter of water and electrolytes — as you cut carbs, the body flushes more fluids and with them sodium, potassium and magnesium. How to manage it day by day is in Keto flu: what it is and how to get through it; which foods to get the minerals from (and when supplements require caution) in Electrolytes on the ketogenic diet.

What the research says: documented benefits

Weight loss: meta-analyses of randomised trials show the ketogenic diet produces greater weight loss than low-fat diets at 6-12 months, with differences that tend to narrow over the long term. The most likely mechanism isn't "metabolic magic" but the combination of greater satiety and less variety of hyperpalatable foods.
Type 2 diabetes and blood sugar: drastically reducing carbs improves blood glucose, glycated haemoglobin and triglycerides, often allowing — under medical supervision — a reduction in medication. Multi-year clinical studies of patients followed with a supervised ketogenic approach show significant remissions in a share of participants.
Drug-resistant epilepsy: the historic and best-documented therapeutic use, especially paediatric, managed in a hospital setting.
Triglycerides and HDL: almost invariably improve; LDL, on the other hand, shows highly variable individual responses (see below).

Risks and contraindications, in brief

An honest guide highlights them, rather than burying them in fine print.

LDL and lipid profile: in a share of people (so-called "lean mass hyper-responders") LDL cholesterol rises markedly. It's not a detail: monitor your lipids with tests before and after 3-6 months, and assess with your doctor.
Who shouldn't start without supervision: pregnancy and breastfeeding, diabetes on medication (particularly insulin or SGLT2 inhibitors), kidney, liver or pancreatic conditions, current or past eating disorders. The full list — with the symptoms that require medical attention — is in Contraindications and side effects.
Anyone taking glucose-lowering or blood-pressure medication must involve their doctor BEFORE starting: keto lowers blood sugar and blood pressure, and doses often need prompt review.
Social sustainability: pizzas, birthdays, travel. Not a clinical datum, but it decides success more than any biomarker: a diet only works if you can actually follow it.

Keto, weight-loss drugs or other diets?

The ketogenic diet isn't the only road and isn't competing with anyone: it's ONE tool, with strengths (satiety, simple rules, fast initial results) and limits (social rigidity, initial adaptation). In the comparison between keto, GLP-1 drugs and peptides we put advantages, disadvantages and real risks side by side, with no cheerleading.

Frequently asked questions

How much weight do you lose in the first month? The first 2-3 kg in the first days are largely water and glycogen: that's normal and it isn't fat. After that, a realistic and healthy pace is 0.5-1% of body weight per week, as with any well-designed diet.

Can I do sport on the ketogenic diet? Yes. Endurance performance adapts well (often after a 2-4 week dip); short, intense anaerobic efforts may remain slightly penalised because they depend on glycogen.

Do I have to count calories? At the start yes, for at least two weeks: it calibrates your eye. Then many people maintain their results by listening to hunger, which is more reliable in ketosis.

Is keto forever? No, and for most people it shouldn't be. Many use it as a phase, then transition to a more flexible low-carb approach while keeping the good habits: real food, adequate protein, rare sugars.

Sources

Article for informative and educational purposes; it does not replace the advice of a doctor or nutritionist.