Lose 5 kg in a month: is it possible?

The short answer: yes on the scale, rarely as pure fat. If you have typed “how to lose 5 kg in a month” into a search bar, you probably have a date in mind (a wedding, a holiday, a medical check-up) and a perfectly reasonable wish to see results quickly. The good news: one month is plenty of time to change direction and watch the number go down. The less good news: not all of those 5 kg on the display are worth the same.

The weight you read every morning mixes several things: fat, muscle, water, whatever is in your gut, and the glycogen stored in your muscles and liver. Some of these can swing by more than a kilo in 48 hours without your fat mass changing by a single gram.

To know what is realistic for you, you need to separate two questions: how much fat can you lose in four weeks, and how many extra kilos might the scale show on top of that. Let’s put numbers on both.

The best-known rule says that one kilo of body fat holds about 7,700 kcal. It is the metric version of the old American rule of 3,500 kcal per pound. Applied to our goal, it gives: 5 kg × 7,700 kcal = 38,500 kcal to “save” in one month, or roughly 1,280 kcal of deficit per day for 30 days.

In practice, a woman who burns 2,000 kcal a day would have to eat around 700 kcal, and a man who burns 2,600 kcal around 1,300 kcal. The first case falls below the threshold of very low calorie diets, which are only done under medical supervision; the second is already very restrictive.

The rule also has limits. Researcher Kevin Hall, from the US National Institutes of Health (NIH), showed that it mainly fits people who carry a lot of body fat. In leaner people, each kilo lost contains more muscle and water, and therefore fewer calories: about 5,900 kcal per kilo for someone carrying 20 kg of fat. The scale then drops a little faster, but not necessarily for good reasons. His dynamic model also reminds us that energy expenditure falls as you lose weight: over the long term, the static rule overestimates weight loss. Over a single month, it remains a good approximation.

Many people lose 1.5 to 2 kg in the first few days of a diet, then see their progress slow down abruptly. Nothing is wrong: what melts away first is mostly glycogen, the storage form of carbohydrates. Your body keeps roughly 400 to 500 g of it in the muscles and liver (an order of magnitude that varies with body size and training), and each gram is stored with at least 3 g of water, according to a study based on muscle biopsies.

When you eat less, especially fewer carbs, these stores shrink and the water bound to them leaves. Add a less full gut and often less salt on your plate, and the scale can show 1 to 2 kg less while your fat mass has barely moved. The reverse also happens: a salty or carb-heavy meal can push your weight up by a kilo the next morning.

To avoid being fooled by these swings, read our guide to water retention and track your seven-day average rather than a single morning’s number.

Here is what the maths gives over four weeks, depending on the average deficit you keep up each day. The “scale” column adds the water and glycogen lost early on, which varies a lot from person to person. You can see that 5 kg on the scale comes within reach at around 1,000 kcal of daily deficit, while 5 kg of pure fat takes more than that.

Health authorities agree. The UK NHS advises losing weight steadily, aiming for 0.5 to 1 kg (1 to 2 lb) a week. The US CDC also says 1 to 2 pounds a week, and points out that people who lose weight at this gradual, steady pace are more likely to keep it off. In France, the food safety agency ANSES warns that weight-loss diets are not a trivial matter and that justified weight loss is best supported by a doctor or a dietitian.

Over a month, that pace means 2 to 4 kg. Less spectacular than 5 kg, but it protects your muscle and your motivation much better. For most people, it comes down to a deficit of 500 to 750 kcal a day, reached by eating a little less and moving a little more.

If you are not sure how to set that number, our guide to the calorie deficit explains step by step how to estimate your needs and choose a sensible gap. The CDC also notes that losing 5% of your body weight, or 5 kg for someone who weighs 100 kg, already improves blood pressure, cholesterol and blood sugar.

The same month does not give everyone the same result. Someone with a lot of excess weight burns more energy every day: their basal metabolic rate and the cost of every movement are higher. A 1,000 kcal deficit can then still leave a comfortable intake, whereas it would be unmanageable for a 55 kg person who burns 1,800 kcal a day. The higher your starting weight, the more plausible 5 kg in a month becomes; the closer you are to a healthy weight, the harder and less desirable it is.

Research backs this up. In an Australian trial published in 2014, 200 adults with obesity lost weight either in 12 weeks on a very low calorie diet or gradually over 36 weeks. Almost three years later, both groups had regained a similar share of the weight lost, around 70%. Losing weight quickly did not lead to more regain, but that programme was run by a medical team.

That is the key nuance: very low calorie diets (under 800 kcal a day) do exist, and the NHS mentions them, but they are not suitable for everyone and should be followed with a health professional, not alone with an app.

When the deficit gets too large, your body does not only draw on fat. Part of the loss comes from muscle, especially if you eat little protein and do no strength training. A meta-analysis of 24 trials shows that a higher-protein diet, at the same calorie intake, limits this loss of lean mass and the drop in resting energy expenditure.

Then come fatigue, irritability, trouble concentrating and a hunger that eventually wins. ANSES has listed other possible effects of restrictive diets on bones, the heart and the kidneys, as well as eating disorders. Very rapid weight loss also raises the risk of gallstones, which medical programmes monitor closely.

Finally, there is yo-yo dieting. According to ANSES, the more diets you go through, the more you encourage weight regain. Our article on eating too little to lose weight explains these mechanisms and the warning signs to look out for.

Here is a sensible plan to aim for 2 to 4 kg in a month, or a little more if you are starting from a higher weight. It relies on six levers: a moderate deficit, protein at every meal, more steps, two strength sessions, enough sleep and regular tracking.

Losing 5 kg on the scale in a month is possible, especially if you start from a higher weight, but some of those kilos will be water and glycogen. Losing 5 kg of pure fat in 30 days takes a deficit of about 1,280 kcal a day, too much for most adults without medical supervision. A pace of 0.5 to 1 kg a week, or 2 to 4 kg in a month, protects your muscle, your energy and your chances of keeping the weight off. Rely on a moderate deficit, protein, steps, strength training, sleep and honest tracking, then judge your progress on averages. And if you have a chronic condition, take medication, have a history of eating disorders or a lot of weight to lose, talk to your doctor or a dietitian first.