The Keto Starter Guide

Most keto guides are either a wall of biochemistry or a list of recipes. This one is neither. It is what you need to know to get through the first month without quitting, in the order you need to know it.

What ketosis actually is

Your body runs on glucose by default, because glucose is easy and there is usually plenty of it. Cut carbohydrate low enough for long enough and the supply runs short. Your liver responds by breaking down fat into ketone bodies, which most of your tissue, brain included, can burn instead. That state is ketosis.

It is not exotic and it is not dangerous for most healthy people. It is a metabolic gear your body already has. Nutritional ketosis usually shows up as a blood ketone reading somewhere between 0.5 and 3.0 mmol per liter.

One thing worth clearing up early. Nutritional ketosis is not ketoacidosis. Ketoacidosis is a medical emergency that happens mainly in people with type 1 diabetes, at ketone levels roughly ten times higher, alongside high blood glucose. The names sound alike and the conditions are not.

Net carbs, and why the label lies to you

Net carbs are total carbohydrate minus fiber, and in most countries minus some sugar alcohols. Fiber passes through largely undigested, so it does not raise blood glucose the way starch and sugar do.

This is where packaging gets slippery. Erythritol and allulose genuinely have almost no glucose effect and can fairly be subtracted. Maltitol cannot. It is used constantly in sugar free bars and chocolate, it raises blood glucose substantially, and subtracting it produces a net carb number that is simply not true. If maltitol appears high in an ingredient list, treat the net carb claim on the front of the package as marketing.

Your numbers

Keep total net carbs under 20 to 25 grams a day to get into ketosis reliably. Some people hold ketosis at 50, but start low and loosen later rather than the other way round.

Eat enough protein. Somewhere around 1.2 to 1.6 grams per kilogram of your target body weight is a sensible range for most people. The old advice to fear protein on keto was overstated, and eating too little of it costs you muscle.

Let fat fill the gap. Fat is the lever you adjust for hunger and energy, not a target to hit. You do not need to pour butter into coffee to make this work.

What to eat

Meat, fish, eggs and shellfish. Cheese, cream, butter, and full fat dairy if you tolerate it. Above ground vegetables, which means leafy greens, broccoli, cauliflower, courgette, asparagus, peppers, mushrooms. Avocado, olives, olive oil. Nuts, with macadamias and pecans the most forgiving and cashews the worst offender. Berries in modest amounts.

What to cut

Sugar in every form. Bread, pasta, rice, oats, cereal. Potatoes and most root vegetables. Beans and lentils. Most fruit. Beer and sweet drinks, including the ones marketed as healthy.

The one that catches people out is sauces. Ketchup, barbecue sauce, teriyaki, most salad dressings and almost every jarred pasta sauce carry more sugar than you would guess. Read those labels before you read anything else.

The first two weeks

Around day three most people feel awful. Headache, fatigue, a short fuse, muscles that cramp at night. This gets called keto flu and it sounds like your body objecting to the diet. It is usually nothing of the sort.

Here is the actual mechanism. Cutting carbs lowers insulin. Lower insulin tells your kidneys to stop holding on to sodium, so you excrete sodium and a lot of water with it, and potassium and magnesium follow. What you are feeling is not carbohydrate withdrawal, it is an electrolyte deficit and mild dehydration.

Which means it is fixable. Salt your food properly, more than feels normal. Drink to thirst rather than to a target. Most people find some combination of sodium, potassium and magnesium each day sorts it out within a couple of days. Our supplements section covers what to look for.

If you take blood pressure medication or have a kidney condition, talk to your doctor before deliberately increasing sodium or potassium. That advice is not boilerplate, it matters here.

Five mistakes that stall people

Not eating enough. Keto suppresses appetite, which is a feature until you are accidentally eating nine hundred calories a day and wondering why you feel terrible.

Hidden carbs. A tablespoon of ketchup, a handful of cashews and a diet drink sweetened with maltodextrin can quietly cost you your whole daily allowance.

Treating sugar free as free. Keto desserts are still food. They still carry calories, and for many people they keep the sugar craving alive rather than ending it.

Weighing yourself daily in week one. The first few pounds are water. So is the gain when you eat one high carb meal. Neither number means what you think it means.

Quitting on day four. That is the day the electrolyte deficit peaks. It is also, almost always, the day before it lifts.

A first week that works

Keep it dull on purpose. Novelty is a week two problem.

Breakfast is eggs cooked in butter, or full fat Greek yoghurt with a few berries, or nothing at all if you are not hungry. Lunch is a big salad with a protein and an olive oil dressing you made yourself. Dinner is a piece of meat or fish with a green vegetable and something fatty on top. Snacks, if you need them, are cheese, olives, macadamias or a boiled egg.

Cook more than you need every time. The single biggest predictor of getting through week one is having something in the fridge at the moment you are hungry and tired.

How to tell it is working

Urine strips are cheap and they are the usual starting point, but understand what they measure. They show ketones you are excreting, and as you adapt you excrete fewer. The strips fade while you are firmly in ketosis, and a lot of beginners read that as failure and quit.

A blood meter is the accurate option and the one worth owning if you are going to track at all. Test at the same time each day, before eating. Our testing gear section covers the cost per strip question, which matters more than the price of the meter.

Honestly though, the best signals are not numbers. Steady energy through the afternoon, hunger that arrives on a schedule instead of ambushing you, and clothes that fit differently tell you more than any strip.

When keto is not the right call

Keto is not a universal answer and anyone who tells you it is wants something from you. Talk to a qualified professional before starting if you are pregnant or breastfeeding, if you take medication for diabetes or blood pressure, if you have kidney or liver disease or have had your gallbladder removed, or if you have a history of disordered eating.

Everything on this page is general information about food and nutrition, not medical advice, and it is not a substitute for it.

Stocking the kitchen

You do not need much to start, and you certainly do not need everything at once. Salt, eggs, butter, olive oil and green vegetables will carry you through the first week.

When you are ready to bake or want the pantry properly stocked, our kitchen staples section covers the flours, sweeteners and fibers worth owning, and snacks and bars covers the thing to keep in your bag for the day everything runs late.