What happens to the body when you lose weight: fat, muscle, water, metabolism, and health

When losing weight, the body doesn't simply "burn fat." In the first few days, a significant portion of the weight change is due to a decrease in glycogen stores and associated water; then, adipose tissue increasingly accounts for the weight loss, but lean mass may also decrease. At the same time, energy expenditure, appetite, hormone levels, insulin sensitivity, blood pressure, and other metabolic indicators change. Therefore, the number on the scale reflects only part of what's happening. [1]

With properly managed weight loss, the primary long-term goal is to reduce excess fat, preserve muscle as much as possible, and improve health. A loss of approximately 5-7% of baseline weight in overweight or obese individuals can improve glucose, blood pressure, and lipid metabolism; more significant, sustained weight loss often yields additional benefits. [2]

The body adapts to the lower mass: it requires slightly less energy, and hunger signals may increase. This is a normal physiological response, not a sign that your metabolism is broken. These changes explain why weight loss typically progresses faster at first, then slows down, and maintaining the results requires a separate strategy. [3]

What exactly decreases when a person loses weight?

Losing weight and losing fat are not the same thing.

Body weight includes:

• adipose tissue;
• muscles and other protein tissues;
• water;
• glycogen;
• bone tissue;
• organs;
• contents of the gastrointestinal tract.

So losing 3 kg on the scale does not automatically mean losing 3 kg of fat.

At the onset of energy restriction, glycogen, water, and sodium change particularly rapidly. As the deficit continues, fat mass becomes an increasingly significant component of the loss. Loss of lean mass is also possible, and its magnitude depends on the size of the deficit, protein intake, initial body composition, and physical activity. [4]

This is why two people who lose 10 kg each can get completely different results: one will lose mainly fat and retain muscle, while the other will lose significantly more lean tissue.

What happens in the first days of weight loss?

The first rapid weight loss is often largely water loss, not solely fat.

When energy intake decreases, especially if carbohydrate intake decreases simultaneously, the body begins to use up glycogen—the stored form of carbohydrate in the liver and muscles. Glycogen holds a significant amount of water, so a decrease in its reserves is accompanied by a decrease in fluid mass. [5]

During the first days of energy restriction, insulin levels may also drop and sodium and water excretion may increase. As a result, weight loss can sometimes be quite dramatic. This is especially noticeable on a low-carb diet, but it also occurs to varying degrees with other energy restriction regimens. [6]

This is why the first week of weight loss is a poor indicator of future speed.

If a person loses 2 kg in the first seven days, this does not mean that he will lose 2 kg every following week.

Why weight may return slightly after the first few weeks

Glycogen stores don't continue to decline indefinitely. After a while, they stabilize at a new level.

If, after several weeks of dieting, a person increases their carbohydrate or salt intake, some of their glycogen and bound water are restored. Weight may increase, although body fat remains virtually unchanged.

For the same reason, after completing a low-carb diet, a person may quickly see a gain of 1-2 kg on the scale—this doesn't necessarily mean the same amount of newly accumulated fat. Changes in hydration are one reason why body composition assessment methods can also yield different results in the first weeks of weight loss. [7]

When fat starts to noticeably decrease

Fat tissue is consumed from the very beginning of a negative energy balance, but after the initial period, water no longer distorts the picture so much, and the contribution of fat loss becomes more noticeable.

Fat in the body is stored primarily in the form of triglycerides inside fat cells called adipocytes.

When additional energy is needed, fatty acids are released from these stores and oxidized. The end products of metabolism are primarily carbon dioxide and water. Carbon leaves the body primarily through the lungs as part of exhaled carbon dioxide, and water is eliminated through urine, sweat, breath, and other fluids. [8]

That is, fat is not “converted into energy,” is not excreted primarily through sweat, and is not converted into muscle.

Energy is released during the chemical oxidation of its molecules, and the atoms leave the body as part of the products of this metabolism.

What happens to fat cells?

When you lose weight, fat cells generally become smaller—they don't disappear in large numbers.

Studies of human adipose tissue show that weight loss reduces adipocyte size. In adults, fat cell number typically changes significantly less than their volume, and after significant weight loss, it can remain elevated compared to a person who was never obese. [9]

This helps to understand one of the interesting aspects of long-term weight control.

After weight loss, fat cells become "emptier," but the adipose tissue itself does not completely disappear. Modern research also discusses persistent changes in its cellular and molecular biology—so-called metabolic or "adipose memory"—which may potentially contribute to the predisposition to weight regain. Not all mechanisms and their clinical significance have yet been fully established. [10]

Do you lose muscle mass when you lose weight?

Yes, lean mass typically decreases during weight loss, but its loss can be significantly limited.

When starting to lose weight, the term "lean mass" is especially misleading. It includes not only muscle protein but also water and glycogen. Therefore, an early decrease in measured lean mass does not mean that a person has lost the same amount of real muscle within a few days. [11]

With a longer energy deficit, some reduction in muscle tissue is actually possible.

The risk is higher when:

• very large energy deficit;
• rapid weight loss;
• insufficient protein intake;
• complete absence of strength training;
• initially low muscle mass;
• old age;
• long-term illness or malnutrition.

Therefore, quality weight loss is assessed not only by the number of kilograms lost.

Why strength training changes the quality of weight loss

Strength training signals the body to maintain functionally essential muscle tissue.

A 2025 meta-analysis of 25 randomized trials found that adding resistance training to dietary weight loss had little effect on total weight loss, but decreased fat-free mass loss, increased fat mass loss, and improved muscle strength.[12]

This explains a situation that sometimes seems paradoxical:

A person who strength trains loses weight on the scale a little slower than expected, but their waistline shrinks, their body fat decreases, and their muscles are better preserved.

From a body composition perspective, this may be a more favorable outcome.

Why is weight loss slowing down?

The smaller the body becomes, the less energy it usually requires.

Energy is spent on the functioning of organs, maintaining temperature, digesting food, physical movement and many other processes.

After losing mass, the cost of moving a lighter body decreases, tissue composition changes, and the total daily expenditure gradually decreases.

Therefore, a diet that created a large deficit at a weight of 110 kg may already create a much smaller deficit after losing weight to 85 kg.

This is why the NIDDK Body Weight Planner model takes into account dynamic changes in energy expenditure. The old linear idea that the same calorie reduction will lead to exactly the same loss every week indefinitely is physiologically incorrect. [13]

What is metabolic adaptation?

In addition to the reduction in energy expenditure due to smaller body size, there is adaptive thermogenesis - an additional reduction in energy expenditure relative to that which would be expected from changes in body mass and composition alone.

This effect is indeed found in studies, but its magnitude varies considerably.

Systematic reviews show that metabolic adaptation is real, but in the best-quality studies it is often modest. This does not mean that the body is able to stop using fat stores during a true, long-term energy deficit. [14]

It would be more correct to say:

The body becomes somewhat more economical, so the initial deficit decreases.

Wrong:

"metabolism is turned off and calories no longer matter."

What happens to appetite?

As people lose weight, they experience increased hunger. This is a physiological compensation, not necessarily a loss of self-control.

Adipose tissue and the gastrointestinal tract are involved in the hormonal regulation of hunger and satiety.

A modern meta-analysis of 127 studies found an increase in total ghrelin levels, a hormonal signal associated with hunger, following weight loss. Several other satiety hormones, including peptide YY and active glucagon-like peptide-1, also showed changes in a direction that could support increased appetite, although results varied across studies. [15]

After a decrease in body fat, leptin, one of the signals of energy reserves, also decreases. A classic long-term study showed that some hormonal changes and a subjective increase in hunger persisted for at least a year after significant dietary weight loss. [16]

This is one of the reasons why the last few pounds are often harder to lose than the first.

Why does the body resist weight loss?

From an evolutionary point of view, a decrease in energy reserves represents a signal to the organism of a potential food shortage.

The nervous and endocrine systems react in several ways:

• increase motivation to search for food;
• alter hunger and satiety signals;
• reduce energy costs somewhat;
• may reduce spontaneous motor activity.

Individual changes are sometimes small, but together they can significantly reduce the initial energy deficit. Modern reviews of the physiology of weight regain consider appetite, energy expenditure, adipose tissue, the nervous system, and metabolic signaling as interrelated mechanisms. [17]

This is why successful weight loss is not just a matter of arithmetic, although energy balance remains its foundation.

What's happening to insulin and insulin sensitivity?

As excess fat mass is reduced, tissue sensitivity to insulin usually improves.

This effect has been particularly well studied in people with insulin resistance, prediabetes, and type 2 diabetes.

The Standards of Care in Diabetes 2026 indicate that a sustained weight loss of approximately 5-7% of baseline weight in overweight or obese individuals improves glycemia and other intermediate cardiovascular risk factors. A more substantial weight loss may provide additional benefits and, in some individuals with type 2 diabetes, promote disease remission. [18]

This does not mean that every person's "insulin levels will normalize" after a certain amount of weight loss.

The effect depends on the duration of diabetes, pancreatic function, degree of obesity, genetics, physical activity and other factors.

Why blood sugar sometimes improves even before major weight loss

Metabolic changes do not always follow strictly parallel weight gain.

Reducing energy intake, increasing activity, and reducing liver fat can improve glucose regulation even before reaching your “ideal weight.”

Moreover, sustained clinically significant benefits typically become more noticeable with a loss of even just a few percent of baseline weight. Current guidelines for people with prediabetes or diabetes often use a target of 5-7%, with a greater reduction in appropriate circumstances potentially yielding additional benefits. [19]

What's happening to blood pressure?

In overweight and obese people, weight loss is often accompanied by a decrease in blood pressure.

The American Heart Association and American College of Cardiology 2026 guidelines consider a 5-10% weight loss as a significant intervention for reducing cardiovascular, renal, and metabolic risk. This reduction is associated with improvements in blood pressure, glycemia, triglycerides, and other risk factors. [20]

If a person is taking medication for hypertension and loses significant weight, their treatment needs may change over time.

You should not stop taking antihypertensive medications on your own, but the appearance of unusually low blood pressure, dizziness when standing up, or weakness is a reason to measure your blood pressure and discuss treatment with your doctor.

What happens to cholesterol and triglycerides?

Reducing excess weight usually improves some of the lipid profile, especially triglyceride levels.

Current US guidelines for cardiovascular-renal-metabolic syndrome indicate that moderate weight loss is associated with improvements in triglycerides and high-density lipoproteins, as well as overall dyslipidemia control.[21]

Moreover, the reaction of individual indicators also depends on the composition of the diet.

For example, a diet high in saturated fat may affect LDL differently than a diet high in unsaturated fat, even if weight loss occurs.

Therefore, positive weight dynamics does not make the quality of nutrition unimportant.

What happens to fat in the liver?

The liver is one of the organs that can respond quite noticeably to the reduction of excess weight.

In metabolically associated fatty liver disease, current European guidelines EASL, EASD and EASO establish fairly specific guidelines.

Overweight people with this disease experience sustained weight loss:

• helps reduce the amount of fat in the liver by approximately 5% or more;
• 7-10% is associated with improvement of inflammatory changes;
• 10% or more increases the likelihood of fibrosis improvement.[22]

This does not mean that every person with fatty liver disease needs to urgently lose 10% on their own.

In cases of advanced fibrosis or cirrhosis, nutrition and weight loss require separate assessment, as excessive muscle loss can be dangerous.

What happens with inflammation?

Excess adipose tissue is more than just a passive energy store. It is a metabolically and immunologically active organ.

Obesity can be accompanied by chronic low-grade inflammation and adipose tissue dysfunction. Reducing excess fat mass can improve some of these processes.

Standards of Care 2026 notes that greater weight loss is associated with improvements in inflammatory and other cardiometabolic parameters, particularly in people with obesity and comorbidities.[23]

However, the phrase "weight loss eliminates inflammation from the body" is overly simplistic. What's at issue is a gradual change in metabolic and immune signals.

What happens to the heart and blood vessels?

Positive changes in blood pressure, glucose, triglycerides, and central adipose tissue together can reduce cardiovascular risk.

Current guidelines consider a 5-10% weight loss in overweight or obese adults to be a clinically significant level for reducing cardiovascular-renal-metabolic risk.[24]

However, weight loss alone does not eliminate the need for treatment:

• arterial hypertension;
• high cholesterol;
• diabetes mellitus;
• smoking;
• other risk factors.

For example, a person with high cardiovascular risk may still require a statin even after successful weight loss.

Why it becomes easier to move

As mass decreases, the mechanical load a person must endure when walking, climbing stairs, and other activities decreases.

Therefore, everyday movement often becomes subjectively easier.

Current obesity treatment standards note that weight loss can improve physical functioning and quality of life. The effect depends not only on the amount of weight lost but also on muscle and overall fitness. [25]

If a person loses a lot of muscle tissue along with fat, weight loss can be dramatic, but strength and functionality can decline.

So "lowest possible weight" is not always the healthiest goal.

What's happening with sleep?

In obese individuals, particularly those with obstructive sleep apnea, significant weight loss can improve the severity of sleep-disordered breathing.

The Standards of Care in Diabetes 2026 indicates that greater weight loss may improve a number of obesity complications, including sleep apnea.[26]

But weight loss is not a guaranteed independent treatment for apnea.

If the diagnosis has already been made, do not discontinue hardware therapy or other treatments simply because weight loss has occurred. A follow-up evaluation by a specialist is necessary.

How weight loss can affect your menstrual cycle

If a woman has obesity and associated ovulation disorders, losing excess weight can sometimes help normalize reproductive function.

This is especially relevant for polycystic ovary syndrome and other conditions associated with metabolic disorders. A current European document on obesity and women's reproductive health indicates that moderate weight loss can improve fertility in obese women. [27]

But the opposite situation is also possible here.

An extreme energy deficit, very low body weight, or intense exercise can disrupt the menstrual cycle. Therefore, the disappearance of menstruation during intensive weight loss is not a sign that the diet is "working very well," but a reason to reassess your diet and consult a doctor.

What happens to medications when you lose weight?

As blood pressure, glucose, and other metabolic parameters decrease, the need for individual medications may change.

This is especially important for people with diabetes.

When treating with medications that can cause hypoglycemia, primarily insulin and sulfonylureas, significant dietary or weight reduction or the addition of effective anti-obesity therapy may require dose adjustments. Standards of Care in Diabetes 2026 recommends reviewing such medications to reduce the risk of hypoglycemia. [28]

You should not change the dosage on your own.

But if during weight loss a person with diabetes begins to experience:

• shiver;
• sweating;
• weakness;
• confusion;
• low glucose readings,
• The treatment plan must be reviewed with your doctor.

Why losing weight too quickly may be undesirable

Faster weight loss does not always mean better results.

A large energy deficit increases the likelihood of insufficient protein and micronutrient intake, loss of lean mass, and poor program tolerance.

This is why NICE considers diets of 800-1200 kcal per day as a specific therapeutic intervention that should be used as part of a comprehensive program with professional support. Diets below 800 kcal are intended only for specific medical situations and should not be used as a standard long-term diet. [29]

Standards of Care 2026 also specifically recommends that during intentional weight loss, adequate nutrient intake, especially protein and micronutrients, be ensured. [30]

Why does rapid weight loss increase the risk of gallstones?

This is a real and well-known risk.

The NIDDK notes that rapid weight loss increases the risk of gallstones. During prolonged fasting or very rapid weight loss, the liver releases more cholesterol into bile, and the gallbladder may empty less efficiently. [31]

This is especially relevant:

• after metabolic/bariatric surgery;
• with very low-calorie diets;
• with high initial obesity;
• with existing stones.

Therefore, severe pain on the right side under the ribs after rapid weight loss, especially after eating and accompanied by nausea, requires medical evaluation.

What changes during weight loss are normal, and which require attention?

Change	It is often explained	What to do
A quick minus in the first days	Glycogen + water	Do not extrapolate the speed over the entire period
Weight fluctuates from day to day	Water, salt, intestinal contents	View average trend
The speed decreased over time	Less weight + adaptation of energy costs	Review the current deficit
I started to feel more hungry	Physiological adaptation of appetite	Improve satiety and nutritional structure
Weight loss, waist reduction, strength maintenance	Favorable change in body composition	Continue the program
Weight is rapidly decreasing, strength is falling sharply	Excessive loss of lean mass is possible	Review your diet and exercise
Frequent dizziness and weakness	Possible excessive deficiency or low pressure	Assess your diet and blood pressure, and consult a doctor if necessary.
Hypoglycemia in diabetes	Treatment may become too intense	Urgently review the therapy with your doctor.
Pain on the right side under the ribs after rapid weight loss	Gallstones are possible	Medical assessment
Menstruation has disappeared	Excessive energy deficit is possible	See a doctor

Does the body "burn muscle first, then fat"?

No.

The body simultaneously utilizes various energy substrates. The proportion of fats, carbohydrates, and protein varies depending on diet, energy reserves, exercise intensity, and the duration of the deficit.

At the beginning of the diet, the sharp decrease in "fat-free mass" is largely due to glycogen and water. With prolonged restriction, the body gradually adapts and increases the use of fat reserves. [32]

But muscle protein can indeed be used up too.

So the question is not whether the body is burning muscle or fat, but rather what proportion of the total loss will be fat and what proportion of the functionally important lean tissue will be fat.

Is it possible to force the body to lose only fat?

It is practically impossible to completely exclude changes in other components of the mass.

But the outcome can be made more favorable.

The most convincing help is:

• moderate and tolerable energy deficit;
• adequate nutrition;
• adequate amount of protein;
• regular strength training;
• maintaining general physical activity.

Resistance training has been particularly well proven to reduce the loss of lean mass during dietary weight loss. [33]

Why does weight sometimes stagnate even though the body continues to change?

Scales are unable to separate fat, water, glycogen and muscle.

For example, a person may lose some fat but retain more water. Overall weight will remain the same.

On the contrary, a rapid loss after several low-carb days can create the impression of a huge loss of fat, although a significant portion is water.

Therefore, to assess what is happening, it is useful to combine:

Average weight dynamics + waist circumference + physical indicators +, if necessary, body composition assessment.

Even methods for measuring body composition have limitations, especially when hydration changes rapidly.[34]

After how many kilograms do beneficial changes appear?

It is better to calculate the dependence not in absolute kilograms, but as a percentage of the original mass.

For a person weighing 70 and 140 kg, the same 5 kg represent a completely different proportion of mass.

For adults who are overweight or obese, current recommendations show a rough pattern:

Steady reduction of initial weight	What changes are becoming more likely?
Any reduction	May be useful depending on the condition
About 5-7%	Improvement of glucose and some cardiovascular risk factors
5-10%	Clinically significant reduction in multiple cardiometabolic risks
>10%	Additional benefits for a range of obesity complications
≥5% in MASLD	Reducing liver fat
7-10% at MASLD	More likely to improve liver inflammation
≥10% in MASLD	Higher likelihood of improving fibrosis

These values do not guarantee a specific effect for each individual. They reflect average research results and recommendations for specific patient groups.

Why Healthy Changes Don't Require an "Ideal Weight"

This is a particularly important practical conclusion.

A person can start at 120 kg, drop to 110-112 kg and still formally be obese, but already have a significant improvement in blood pressure, glucose, triglycerides or liver fat.

Therefore, modern medicine increasingly views success less and less as simply achieving a “normal body mass index.”

Standards of Care 2026 proposes assessing health, complications, waist circumference, quality of life, and other clinical goals along with weight.[35]

What happens when weight loss stops?

After some time, the energy deficit decreases.

This is facilitated by:

• less weight;
• lower energy consumption;
• metabolic adaptation;
• increased appetite;
• possible reduction in daily activity.

As a result, the new mass gradually approaches the point at which energy intake and expenditure again become similar.

This is how a weight plateau occurs.

It does not mean that the body “refuses to lose weight.” The energy balance conditions have changed. [36]

What happens after you finish losing weight?

After achieving the goal, the body does not immediately return to its original physiological state.

Appetite may remain increased, energy expenditure may correspond to a smaller body, and some adaptive changes may persist.

Current data on the physiology of weight loss show that these processes occur regardless of how weight loss was achieved - through lifestyle changes, medications, or surgery. [37]

Therefore, weight maintenance is a separate stage.

Returning to the previous diet that initially resulted in excess weight often means returning to a positive energy balance.

What is often misunderstood

"I lost 3 kg of fat in the first week."
Not necessarily. In the beginning, a significant portion of the loss may be due to glycogen and water. [38]

"Fat turns into muscle."
No. They are different tissues. Fat triglycerides are oxidized to carbon dioxide and water; muscles may simultaneously increase in size during exercise, but fat is not converted into muscle fibers. [39]

"Fat is excreted in sweat."
Only a portion of its metabolic products leaves the body as water. The bulk of the carbon is excreted through the lungs as carbon dioxide. [40]

"The faster the weight loss, the better."
No. Too aggressive a deficit increases the risk of malnutrition and loss of lean mass, and rapid weight loss increases the risk of gallstones. [41]

"When you lose weight, your metabolism breaks down."
No. Energy expenditure naturally decreases due to your lower mass and can further adapt slightly. This is part of normal physiology. [42]

"If you're hungry more, it's because you lack willpower."
No. After losing weight, hormonal changes in appetite signals do occur. [43]

"The main thing is to lose as many kilograms as possible."
Not quite. Clinically, it's more important to reduce excess fat, preserve muscle, and improve health.

How to make changes in the body more favorable

There is no way to guarantee that you will lose only fat, but you can tip the balance in the right direction.

For most adults, the logic goes like this:

• create a moderate sustainable energy deficit;
• ensure adequate nutrition and sufficient protein;
• include power loads;
• maintain normal physical activity;
• Avoid extremely low calorie diets without medical supervision;
• evaluate not only weight, but also waist size, physical strength and health status.

The current NICE and Standards of Care 2026 recommendations place emphasis on the adequacy of the diet, long-term sustainability of the strategy and the prevention of protein and micronutrient deficiencies. [44]

When weight loss can no longer be considered normal physiology

A routine medical assessment is necessary if, while trying to lose weight, the following occurs:

• persistent severe weakness;
• frequent dizziness or fainting;
• significant decrease in muscle strength;
• cessation of menstruation;
• persistent vomiting or inability to eat normally;
• attacks of pain on the right side under the ribs;
• repeated episodes of hypoglycemia;
• signs of severe malnutrition;
• losing weight too quickly without a planned large deficit.

If a person loses weight without intention, especially with a normal or increased appetite, this is a different clinical issue. Unexplained weight loss can accompany endocrine, gastrointestinal, infectious, oncological, and other diseases and requires a separate diagnosis.

Key points from experts

Steven B. Heymsfield, MD, is the Boyd Professor and director of the Metabolism and Body Composition Laboratory at Pennington Biomedical Research Center. His research focuses on human energy balance, body composition, and obesity treatment. Research in this area shows that weight loss is not a homogeneous mass: the proportions of fat, water, and lean mass change over time, especially dramatically at the onset of energy restriction. [45]

Stuart Gray, PhD, is Professor of Muscle and Metabolic Health at the University of Glasgow. His research focuses on muscle mass, metabolic health, and physical activity. In a 2025 meta-analysis, for which Gray was the senior author, the research team showed that resistance exercise during dietary weight loss helps maintain lean mass and increases fat loss, even though there is little additional reduction in overall weight. [46]

Marleen van Baak, PhD, is a professor emeritus at Maastricht University and a researcher in the physiology of obesity and energy metabolism. In a 2025 review of the physiology of weight regain, van Baak and Edwin Mariman describe ongoing research into neural, hormonal, immune, and metabolic changes following weight loss and emphasize that many proposed mechanisms of weight regain are still based primarily on associative data. [47]

Frequently Asked Questions

What does the body start to use first when losing weight?

There's no single fuel that's activated first. The body constantly uses a mixture of carbohydrates and fats, and the proportion of each varies. During the first few days, glycogen and bound water stores are particularly depleted, so weight loss can be faster than fat mass. [48]

How many days does it take for fat to start burning?

Fat reserves are used from the onset of a negative energy balance. There's no such thing as a day when the body "doesn't touch fat" and then suddenly starts using it.

Where does the fat go?

During the oxidation process, triglycerides are converted primarily into carbon dioxide and water. Most of the carbon leaves the body with exhalation. [49]

Why does weight loss occur so quickly at the beginning of a diet?

Mainly due to changes in glycogen, water and sodium in addition to fat loss.[50]

Why does weight loss slow down later?

The body becomes smaller, its energy expenditure decreases, adaptive thermogenesis may occur, and appetite often increases. [51]

Are muscles being lost?

Some loss of lean mass is possible. Strength training can help reduce this. [52]

Is it possible to lose weight without losing muscle?

This is impossible to guarantee, especially with significant weight loss. However, adequate nutrition and resistance training significantly improve the retention of lean mass.

Why did I start to want to eat more after losing weight?

This may be part of a physiological adaptation. Studies show an increase in ghrelin and changes in some other hormonal appetite signals after weight loss. [53]

Does losing weight improve metabolism?

If "metabolism" refers to insulin sensitivity, glucose, blood pressure, lipids, and fatty liver disease, many indicators may indeed improve in obese people. But overall energy expenditure typically declines as the body becomes smaller. [54]

Is your liver condition improving?

In metabolically associated fatty liver disease, weight loss of approximately 5% or more is associated with a reduction in liver fat; greater gains may improve inflammation and the likelihood of improving fibrosis.[55]

Can losing weight lower blood pressure?

Yes, in people who are overweight or obese, this is a common beneficial effect. [56]

Is it dangerous to lose weight too quickly?

Very rapid weight loss can increase the risk of lean body mass loss, malnutrition, and gallstones. Very low-energy diets should only be used in specialized programs under medical supervision. [57]

Why does my weight stay the same even though my waist is getting smaller?

Body composition may change, with fat mass decreasing and lean tissue being better preserved. This is especially possible with strength training. [58]

Does metabolism return to normal after finishing the diet?

Some adaptive changes may wane after weight stabilizes, but a smaller body still requires less energy and some appetite changes may persist.[59]

Main

Weight loss is a dynamic restructuring of energy metabolism, not a simple disappearance of fat tissue. During the first few days, glycogen and water levels decrease especially rapidly. Subsequently, fat increasingly accounts for the loss, but with a poorly designed program, a significant amount of lean mass can also be lost. [60]

As weight is lost, energy expenditure decreases and compensatory appetite signals are enhanced. Simultaneously, glucose, blood pressure, lipid metabolism, fatty liver disease, and other obesity-related disorders can improve in overweight or obese individuals. [61]

Therefore, a more informative question is not only “how many kilograms have I lost?”, but also:

How much fat is lost → how much muscle is preserved → is the waist reduced → is strength maintained → are health indicators improved → is the chosen regimen maintainable long-term.

It is this combination that better reflects what actually happens to the body during healthy weight loss.