Can you lose 5 kg in a week?

If the scale drops 5 kg in a week, is that 5 kg of fat?

No. A large drop on the scale in the first week of a diet is real, and it is mostly not body fat. It comes from two sources that change quickly and refill just as quickly.

Glycogen and the water stored with it

Weight often falls more quickly in the first week or two, partly because of changes in body water. Your body stores carbohydrates as glycogen, which is stored together with water. When glycogen stores decrease, some of that water is lost too, and a diet that cuts carbohydrates sharply empties these stores within days.

Food and fluid in the gut

Eating much less, or cutting salt sharply, also reduces the food and fluid in the digestive system and the water the body holds. Each of these can move the scale by a kilo or more without any change in body fat. Once you eat normally again, glycogen, water and gut contents return, which is why fast results so often reverse within days.

What would losing 5 kg of fat in a week require?

A kilogram of body fat corresponds to roughly 7,700 calories of energy, so 5 kg would need a deficit of around 38,500 calories in seven days, or around 5,500 calories a day. That is more energy than most adults use in a day, so even eating nothing would not produce it for most people. Our article on how many calories to lose 1 kg explains the arithmetic and why it is an approximation.

Why can very fast weight loss cost more than fat?

MedlinePlus, published by the US National Library of Medicine, states that losing more than 0.5 to 1 kg a week is not safe for most people, and that rapid weight loss can mean losing muscle, water and bone density. Larger calorie deficits can increase the amount of lean tissue lost alongside body fat.

The National Institute of Diabetes and Digestive and Kidney Diseases states that losing weight very quickly may raise your chances of forming gallstones. Very restrictive diets can also be associated with fatigue, poor concentration, hair thinning and menstrual changes. Severe restriction is also difficult to sustain, and weight regain is common when previous eating patterns return.

What if you have a deadline?

If you have a wedding, a trip or an event in a week, the scale can show a small drop from eating well and reducing salt, and that change is mostly water. We do not recommend very low calorie diets, fasting protocols or dehydration to meet a date. Athletes making weight for a competition should take advice from their sports medicine team.

A deadline several weeks or months away allows a more realistic plan. If your target and deadline do not match, your endocrinologist can discuss whether to adjust the target, extend the timeframe, or reassess the plan based on your response.

What is realistic instead?

The US Centers for Disease Control and Prevention states that people who lose weight at a gradual, steady pace of around 0.5 kg to 1 kg a week are more likely to keep it off than people who lose it faster. At that pace, 5 kg of body fat is a target measured in weeks to months, and our article on how to lose 5 kg in a month covers how a faster but realistic month can be planned.

Endocare’s endocrinologists typically observe three to four kilos a month in patients on a medically supervised programme, and our article on how much weight you can lose in a month explains what changes that number.

When is weight that will not move a medical question?

If your weight is not changing despite a consistent plan, it may be worth reviewing both the plan and whether any medical factors could be contributing. Thyroid disease can affect metabolic rate and make weight management more difficult, but it is treatable once diagnosed. Insulin resistance can also make weight loss more challenging and is often associated with increased waist circumference. Polycystic ovary syndrome (PCOS) affects around one in ten women of reproductive age and can influence weight and metabolism. Certain prescription medications can also contribute to weight gain.

Blood tests can show which of these applies. Our page on thyroid conditions and weight explains how our endocrinologists assess the thyroid.

Frequently asked questions

Is it normal to lose 5 kg in the first week of a diet?

It can happen, particularly at a higher starting weight or on a diet that cuts carbohydrates sharply, although a drop of that size is not common. Most of that drop is glycogen and water, and weight loss does not necessarily continue at the same rate. A rapid shift may also reflect dehydration or illness, and it sometimes warrants assessment by your doctor.

Is losing 5 kg in a week safe?

Not as body fat. MedlinePlus states that losing more than 0.5 to 1 kg a week is not safe for most people, and rapid weight loss can mean losing muscle, water and bone density. A drop on the scale that is mostly water usually returns once you eat normally again. A rapid shift may also reflect dehydration or illness, and it sometimes warrants assessment by your endocrinologist.

Is the weight I lost fat or water?

In a single week, mostly water and glycogen. Body composition analysis estimates body fat, muscle mass and body water. Repeated measurements show what has changed beyond the number on the scale.

Will the weight come back?

The water often returns once you eat normally again, and this is expected. Body fat lost through a sustained deficit does not return in the same way, which is why a gradual plan gives a more lasting result.

How long does it take to lose 5 kg of fat?

At a gradual rate of 0.5–1 kg a week, losing 5 kg would take roughly five to ten weeks. The scale may drop faster at first because of water loss.

What if my weight will not move?

If your weight is not changing despite a consistent plan, it may be worth reviewing both the plan and whether any medical factors could be contributing, such as thyroid disease, insulin resistance, PCOS or certain medications. A consultation can check these.