Ketosis weight loss per week: guide and long-term goals

What is ketosis?

When you eat carbohydrates (such as bread, pasta, rice, and fruit), they are broken down into glucose, which the body uses as fuel. The brain normally uses around 100–120 grams of glucose per day. If you reduce your carbohydrate intake sufficiently, the body begins to adapt to ensure that the brain still receives enough energy. The brain cannot use fat directly as a fuel source, so the body needs to solve this in another way.

It does so by increasing fat breakdown in the liver, where so-called ketone bodies (ketones) are produced. Ketone bodies are small molecules that can be used as fuel by the brain and other organs when little glucose is available. They act as an alternative fuel for the brain and reduce the need to break down muscle protein into glucose.

When the level of ketones in the blood rises and the body primarily uses fat and ketone bodies instead of glucose as fuel, the body is said to be in ketosis. Blood ketone levels are then usually between 0.5–3 mmol/L.

When does ketosis occur?

Ketosis is a normal physiological adaptation that can occur during fasting, starvation, intense exercise, or when following a diet very low in carbohydrates. However, ketosis can also develop in untreated type 1 diabetes, where a lack of insulin leads to uncontrolled ketone production. In such cases, ketone levels can rise to 5–10 times higher than in normal ketosis and lead to ketoacidosis – a serious, life-threatening condition that should not be confused with the harmless ketosis that occurs during dietary changes.

What is a ketogenic diet?

A ketogenic diet is a diet in which most of the energy comes from fat and very little from carbohydrates. It differs from other low-carbohydrate diets, such as LCHF, because carbohydrate intake is much lower and more strictly regulated. Often, carbohydrate intake is limited to a maximum of 50 grams per day, and sometimes as little as 20 grams per day, to induce ketosis.

The aim is to shift the body’s energy use so that fat becomes the primary fuel source instead of carbohydrates. In many approaches, fat accounts for around 70–80 % of total energy intake and protein about 15–20 %, although this can vary.

Typical foods include meat, fish, seafood, eggs, cheese, cream, crème fraîche, butter, olive oil, avocado, nuts, seeds, and low-carbohydrate vegetables. At the same time, carbohydrate sources such as bread, potatoes, pasta, and rice are limited or excluded, as well as sweets like cakes, sweets, and ice cream.

Signs that the body has entered ketosis

To be certain that the body is in ketosis, ketone bodies need to be measured in blood, urine, or breath. However, there are signs that many people recognise as the body adapts.

During the first weeks, when the body starts producing ketone bodies, many people experience increased fatigue, reduced energy, dizziness, headaches, and nausea – a state sometimes referred to as the “keto flu”. Other common signs include increased urination, dry mouth, and sometimes a distinctive breath odour, known as “keto breath”.

Some people may also experience digestive issues at the beginning, such as constipation, as low fibre intake and changes in fluid balance affect the gut. Once the body has adapted to ketosis, some people report increased energy and feeling more alert.

How does ketosis affect weight loss?

Ketosis means that the body starts using more fat as fuel – often described in everyday terms as “increased fat burning”. However, this does not automatically mean that body fat decreases. On a ketogenic diet, fat intake is usually high, and the body primarily uses dietary fat as its energy source. If you consume more energy than you expend, you can be in ketosis without losing weight.

To reduce body fat, even on a ketogenic diet, you need to maintain an energy deficit over time. That said, a ketogenic diet may make weight loss easier for some people, for example through:

• reduced appetite and increased satiety – hormonal changes during ketosis reduce hunger, and ketone bodies themselves may have an appetite-suppressing effect
• fewer foods that trigger overeating, as keto excludes many energy-dense and sweet products
• higher protein intake in some keto approaches, which increases feelings of fullness

Ketosis and weight loss per week – how much can you lose on a ketogenic diet?

In the short term, especially during the first few days on a ketogenic diet, much of the weight loss is due to depletion of glycogen stores in the liver and muscles when carbohydrate intake is low. Glycogen binds a large amount of water, and when these stores are depleted, the body releases fluid. This can lead to a rapid drop in weight at the start – sometimes up to 1–2 kg in the first week.

This results in quick changes on the scales, which can increase motivation.

Research shows that ketogenic diets often lead to slightly greater weight loss than other diets during the first six months – on average around 2–3 kg more. However, this initial advantage is temporary, and after 12 months the difference in weight loss compared with other diets tends to disappear.

Long-term weight loss with a ketogenic diet

In a meta-analysis of 13 studies where participants followed a ketogenic diet, the average weight loss was 0.91 kg greater than with a low-fat diet after 12 months. The effect was small, and researchers emphasised that adherence to the ketogenic diet was often low over time.

In most studies, participants gradually increased their carbohydrate intake, and at the final follow-up many were no longer within the range considered ketogenic. This suggests that it can be difficult to maintain a very strict low-carbohydrate diet in the long term.

Other health effects of a ketogenic diet

During the first 6–12 months, several studies show that a ketogenic diet may improve various health markers, such as lower blood pressure, improved long-term blood sugar control (HbA1c), and changes in blood lipids – often lower triglycerides and higher HDL.

After about one year, however, these effects tend to diminish or disappear, and research no longer shows clear or statistically significant improvements. Much of the benefit appears to be linked to weight loss itself. It is therefore unclear whether these effects persist once weight stabilises – or if no weight loss occurs.

Ketosis and medical treatment of obesity

Ketosis can occur in connection with medical treatment for obesity, particularly when medication leads to a marked reduction in appetite and therefore a large energy deficit. When energy intake is greatly reduced – and often carbohydrate intake as well – glucose availability decreases, glycogen stores are depleted, and the liver produces more ketone bodies.

In this situation, ketosis can occur during rapid weight loss even without following a strict ketogenic diet. For otherwise healthy individuals, this type of ketosis is harmless, temporary, and a normal part of the body’s adaptation to significant weight loss.

Risks and safety

In the short term, ketosis itself is not dangerous for healthy individuals with normal insulin production. For people with certain metabolic, hormonal, or medical conditions, however, ketosis may be unsuitable and should be discussed with healthcare professionals.

From a longer-term perspective, there may be negative health aspects to following a ketogenic diet with the aim of staying in ketosis. The diet is often restrictive, excludes many nutrient-rich foods, and may therefore increase the risk of nutrient deficiencies. A high fat intake combined with low fibre intake can contribute to gastrointestinal problems such as constipation, gas, bloating, or diarrhoea. The risk of gallstones may also increase with a ketogenic diet.

Although “good” HDL cholesterol often increases on a ketogenic diet, an increase in “bad” LDL cholesterol and VLDL is also commonly seen, which may increase the risk of cardiovascular disease. Choosing healthy fats is therefore particularly important on a ketogenic diet.

Most existing studies are small, short-term, and of limited quality, which means there is a lack of strong scientific evidence supporting ketogenic diets as a long-term treatment.

Summary

Ketosis is a natural metabolic state in which the body uses fat as fuel and produces ketone bodies. For some people, ketosis may support weight loss through reduced energy intake, lower hunger, or improved blood sugar regulation.

A ketogenic diet can lead to rapid weight loss and improved blood lipids and blood sugar levels in the short term – particularly during the first 6–12 months. In the long term, however, weight loss often becomes similar to that achieved with other approaches, and improvements in health markers tend to diminish as weight stabilises.

Ketosis should be viewed as a possible part of a broader health strategy – not as a standalone method or a requirement for long-term success.

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