How fast should you lose weight?

Search "how to lose weight fast" and you get "5 kg in a week" or "10 kg in 7 days". It sounds tempting, and the scale can do something like it. Those numbers are not what you think. Here is what a fast drop actually is, what pace makes sense, and how to use a quicker start without setting up the next six months.

Short answer: The scale can drop several kilos in a few days, and almost all of that is water and glycogen. It comes back when normal eating returns. A kilogram of body fat is about 7,700 kcal (calories), so real fat loss is hundreds of grams a week. A sane pace for most people is about 0.3 to 0.7 kg a week.

Why 5 kg in a week is possible, and why it should not excite you

Yes, the scale can fall by several kilos in a few days. Almost all of that loss is not fat. Cut carbs and calories and the body first burns stored carbohydrate (glycogen) in muscle and liver. About 3 grams of water are bound to each gram of glycogen. Add less food in the gut, and water shifts from salt and hormones.

The scale shows a nice drop. You feel motivated. Fat loss was small. Go back to normal eating and the glycogen and the water refill. The kilos return, and you did not "fail". It is physics, not weak will. Day-to-day noise on the scale is in why your weight fluctuates.

How much fat can you actually burn? One kilogram of body fat holds about 7,700 kcal. Even with an honest calorie deficit we are talking about hundreds of grams of real fat a week, not kilos. Fast numbers on the scale are mostly water and glycogen: useful feedback, not the score.

What going too fast takes from you

An extreme deficit looks great on paper. You pay for it. The harder you push, the more the things that bring you back start working, often to a higher weight than you started from.

• Hunger and cravings. A sharp cut raises hunger and lowers fullness. You can hold it with willpower for a few days. Willpower is not infinite, and one evening it gives.
• Muscle loss. If the deficit is too fast and protein and lifting are missing, the body gives up muscle, not only fat. Muscle is what holds your burn and your shape. How to keep it is in build muscle in a calorie deficit.
• Fatigue. Too little energy means worse training, mood and sleep. Few people last more than a few weeks like that.
• The rebound. After a crash diet the weight usually comes back, and so does the frustration. That is yo-yo dieting. The method failed, not you.

A pace you can keep

For most people a sane pace is about 0.3 to 0.7 kg a week, roughly 0.5 to 1% of body weight. It sounds slow next to "10 kg a month". It is the pace where the loss is mostly fat, not muscle, and that you can hold for months, not for three days.

The more fat you have to lose, the faster the start usually is. A leaner person chasing the last few kilos has to go slower and be more patient. Do not compare yourself with someone who is somewhere else.

And do not judge one day on the scale. Weight moves with water, salt, the cycle, and whether you have been to the bathroom. Watch the average over a week or two. You do not have to ban foods. Flexible dieting works: macros and the total, not a forbidden list. Set the deficit in calorie deficit: how much to eat, or estimate it with the calculator.

When a faster start makes sense

A faster start is not banned. Sometimes it helps motivation. If you have a medical reason to lose faster, talk to your doctor. Do not take the pace from an article. The trick is to do the fast phase in a way that does not collapse a few weeks later.

• Enough protein. About 1.6 to 2.2 g per kg of body weight a day. Protein holds fullness and muscle. More in how much protein.
• Strength training. It tells the body "keep the muscle". Without it, a fast deficit costs you more muscle.
• Do not dig the deficit endlessly. Even on a faster start, leave room to cut more later when things slow down.
• Put a time limit on it. Treat the faster phase as a few weeks, not a permanent mode. Then move to a pace you can keep.

You can lose weight quickly. The first kilos are mostly water and glycogen, not fat. Lasting fat loss runs at a pace you can breathe in: enough protein, lifting, a milder deficit, and patience with the scale. Boring, maybe. It works, and it does not bounce back the same way.

Frequently asked questions

Can you really lose 5 kg in a week?

The scale can drop by 5 kg, and it is mostly water and glycogen, not fat. Real fat comes off in the order of hundreds of grams a week. When you eat normally again, the water returns. That is why the fast numbers do not last.

What pace of weight loss is sane?

For most people about 0.3 to 0.7 kg a week, roughly 0.5 to 1% of body weight. That pace spares muscle, keeps hunger tolerable, and can be held for months. Watch the weekly average, not one morning.

Why did the weight come back after a fast diet?

The water and the glycogen came back, and often the urge to make up for weeks of hunger came back too. That is the yo-yo, and it is not a character flaw. It is what a too-hard plan does. The fix is a slower pace you can keep.

Sources, so you can check:

1) Figures in the article: about 3 g of water bound to each gram of glycogen; about 7,700 kcal in 1 kg of body fat

2) Pace in the article: about 0.3 to 0.7 kg a week, roughly 0.5 to 1% of body weight; protein 1.6 to 2.2 g per kg

Martin Barna

Online nutrition and fitness coach. Since 2013 I have helped 600+ people lose fat and keep the result. Science, not crash diets.

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This article is for information only. It is not medical advice. If you have a health condition, talk to your doctor.