Understanding weight as a whole: every building block at a glance

You step on the scale in the morning. The same number as three weeks ago.

And yet you really did eat less. You took the stairs instead of the lift. You left the bread on the table even though it smelled good. And still there is that number, unimpressed by everything you did.

Then comes the sentence you probably already know. Eat less, move more. It is even correct in physical terms. It just explains about as much as the observation that an account gets emptier when you withdraw more than you pay in.

Many people know this pattern. In my consultations the conversation almost always begins with the same question: what am I doing wrong?

So I do not start with a plan. I start with a map. Because weight is not a switch, it is a control system with many adjusting screws. Some of them are well studied. Others are mechanistically plausible but thin on human evidence. And others again are made bigger on the internet than the data allow.

This text sorts that out. It picks up each building block once, says how well documented it is, and then sends you on to the article that covers it in depth.

Why "eat less, move more" falls short as an explanation

Let us start with what is true. If you take in less energy than you use over a longer period, your weight falls. That is thermodynamics and nobody argues with it, myself included.

The problem lies elsewhere. Energy balance is bookkeeping. It tells you that the numbers add up in the end. It never tells you why you were standing at the fridge at half past ten last night without being hungry at all. And it does not tell you why your body suddenly burns less than before after eight weeks of dieting.

Both have been measured. And remarkably cleanly.

Now it gets interesting. Because the same research group showed ten years later what this counter-regulation hangs on.

And then there is the part nobody feels. Because your body cares not only about how much you eat. It also cares about how much you move without noticing.

That leaves the study most often quoted online and most often misunderstood.

Why does a body defend a weight that harms it at all? The most honest answer is: because it was built for a different problem than yours. For most of human history, scarcity was the danger and not abundance. A system that reads every loss as a threat and pushes back was an advantage for a long time. Today the same regulation sits in a world where food is available without pause.

That is not an excuse. It is an explanation for why willpower regularly comes off worse at this point. Willpower is a conscious resource. Counter-regulation runs unconsciously and around the clock.

More on the concept of the calorie and its limits is in the calorie myth and in a calorie is not a calorie. Here we continue with the building blocks themselves.

The building blocks, part 1: blood sugar, insulin and the satiety hormones

Picture your fat tissue as a warehouse. Insulin is then the person at the loading bay who takes goods in and keeps the doors shut while deliveries are arriving. As long as insulin is high, storage happens and little is released. That is not a conspiracy, that is the normal job of the hormone.

After a meal, blood sugar rises, insulin goes up, the sugar disappears into the cells. If that happens often and forcefully, the response of the cells can weaken over time. Then it takes more insulin for the same effect. That is called insulin resistance, and it is one of the most common findings of all in weight topics.

In practice, a permanently high insulin level means two things. The warehouse stays in intake mode. And the blood sugar curve becomes more restless, with deeper troughs after the peaks. It is exactly these troughs that you feel as sudden craving, often two to three hours after eating.

How you can read and influence this curve is covered in detail in insulin resistance and weight loss, in avoiding blood sugar spikes and in what a CGM sensor shows.

Leptin: the signal that arrives and is not answered

Leptin is the fill-level gauge. Fat tissue releases it, the brain reads off how full the stores are. That sounds like a perfect solution: a lot of fat, a lot of leptin, little hunger.

Except it does not work that way in obesity. And the reason has been known since 1996.

How long this shift lasts after a diet was measured by an Australian research group. The figure from it appears on hardly any German advice page.

GLP-1, PYY and ghrelin: the reporting chain around the meal

Alongside insulin and leptin, a second system works on a much shorter cycle. Ghrelin comes mainly from the stomach and reports hunger. It rises before the meal and falls afterwards. GLP-1 and PYY come from the gut as soon as food arrives there, and they report satiety to the brain.

These three are the reason why one meal carries you for a different length of time than another, even though the same amount of energy was on the plate. What keeps the gut busy longer reports satiety longer. What slipped through in five minutes reports almost nothing.

And this is exactly the system the GLP-1 injections act on. They mimic GLP-1. We come to that in detail later. All that matters here: this is not an exotic foreign body in metabolism, it is the amplification of a signal that is already there.

If you want to go deeper: appetite regulation: hunger and satiety explains the reporting chain in detail, food cravings takes on the attacks themselves, and GLP-1 the natural way shows what the body can do here on its own.

The building blocks, part 2: stress, sleep and the body clock

There are phases in which everything shifts at once. Work picks up, the nights get shorter, dinner moves later. And suddenly there is a belly that was not there before, even though nothing changed on the shopping list.

Many people know this sequence. First the stress, then the sleep, then the weight. Scientifically, though, these two building blocks are documented very differently well, and I want to make that difference visible.

Cortisol: real, but smaller than its reputation

Cortisol is the hormone that gets you going in the morning and provides energy under strain. Under lasting strain it stays raised, and then it shifts two things: appetite towards quickly available energy, and fat distribution towards the abdomen.

How to read this: [mechanistically plausible, associations small]. Cortisol is a player, not a main cause. If someone tells you that your weight comes from stress alone, that goes beyond the data. I describe the link between the stress axis and blood sugar in nutrition, blood sugar and cortisol, and the axis itself in cortisol and the HPA axis.

Sleep: the most cleanly measured building block in the whole field

With sleep the situation is different. Here there are controlled laboratory studies in which everything stayed the same except time in bed. That is the kind of design that suggests causality rather than mere association.

Why this happens can even be traced into the fat cell.

That leaves the question of whether all this holds outside the sleep laboratory too. There has been an answer to that since 2022, and in my view it is the most important figure in this whole chapter.

How sleep, the gut and the body clock connect is covered in sleep and the gut microbiome.

The building blocks, part 3: thyroid, menopause, PCOS and testosterone

There is a sentence I hear often: I had everything tested, it was all normal. And still the body has changed. This section sits exactly in that gap.

The thyroid: important, but rarely the whole explanation

Thyroid hormones set the baseline speed of metabolism. When they are missing, everything slows down, energy expenditure included. Overt underactivity should therefore be ruled out when weight rises without an obvious reason.

Beside this stands an observation that shows why the topic does not end with TSH.

How to read this: [observational data, no treatment recommendation can be derived]. This cohort comes from a single region and rests on screening examinations, so with self-selection. It shows associations and justifies a question, not a therapy. Anyone already taking a thyroid preparation changes nothing about it on their own. Every adjustment belongs in a medical conversation and needs medical follow-up.

Which values are worth measuring and how to read them is covered in thyroid values: which ones really count. The view on symptoms with unremarkable values is in functional thyroid underactivity.

Menopause: distribution changes before the number does

Many women describe the same course. Weight stands almost still, but trousers fit differently. That is exactly what has been measured.

With PCOS the connection runs the other way round. There, insulin resistance often stands at the beginning and shifts the hormonal situation with it. How to recognise and measure that is covered in understanding PCOS and in insulin resistance in women. On the symptoms of the transition itself: menopause.

Testosterone in men: a circle that runs in both directions

Abdominal fat and low testosterone often occur together in men. In fat tissue, testosterone can be converted into oestrogen via the enzyme aromatase, and the changed hormonal situation can in turn favour storage. A circle that can feed itself.

This is covered in detail in overweight, insulin resistance and testosterone.

The building blocks, part 4: silent inflammation, microbiome, medication and muscle mass

Now come the building blocks where the quality of the evidence differs most widely. That is why each point in this section states what it rests on.

Silent inflammation and visceral fat

Fat tissue is not a storeroom. It is an active organ that releases messengers and attracts immune cells. That is where the term silent inflammation comes from: no fever, no redness, but a permanently slightly raised background noise in the immune system.

Where this fat sits appears to say more than its total amount. A review from 2024 summarises that several epidemiological studies have shown a clear association between visceral fat and cardiovascular disease, while the data for liver fat remain inconsistent. So the two do not belong in the same pot.

How to read this: [partly contradictory data]. Silent inflammation is well founded as an accompanying phenomenon. As the sole cause of a weight it does not hold up. Covered in detail in silent inflammation and weight.

The microbiome: the weakest building block, named honestly

Hardly any topic is told so large in the weight context and is so thinly documented in humans. I consider this one of the points where integrative medicine should examine itself critically.

How to read this: [mechanistically plausible, human studies thin]. The gut still stays interesting, just for questions other than the number on the scale. What fermented foods can actually move there is covered in fermented foods and the microbiome.

Medication: the building block almost nobody checks

When weight rises without an obvious reason, it is worth a look at your own medication list. That is quantified, in one of the largest analyses available on it.

Muscle mass and resting expenditure

Muscles are the tissue that needs energy even at rest. They are also the largest taker of sugar from the blood. Anyone who loses muscle mass loses both: a part of resting expenditure and a part of the buffering capacity for blood sugar.

That is exactly why muscle comes up again at several points in this text. With too little sleep, the loss shifts towards fat-free mass. Under GLP-1 injections the same question arises. And in menopause, lean mass declines measurably while fat mass rises.

What strength training in the second half of life can contribute is covered in strength training after 40. You will deliberately not find specific training volumes in this text, because they belong to the individual and not in an overview article.

The quality of food: why the same calorie lands differently

You probably know both states. The dinner after which you are back in the kitchen three hours later. And the other one, after which you do not think about food until the next morning. On paper both may have contained the same amount of energy.

For exactly this observation there is perhaps the most elegant study in the whole topic.

Whether this translates into disease rates over years cannot be tested in inpatient studies. That needs cohorts. A meta-analysis of prospective cohort studies pooled 25 reports and calculated the relative risks for diabetes, high blood pressure, lipid disorders and obesity at high against low intake of ultra-processed foods, assessed with the NutriGrade procedure. Observational data document no cause. They show that the direction from the inpatient study is found again in the population.

Why real food satisfies differently is covered in unprocessed food and satiety and in inflammatory foods.

Protein: the nutrient that works through satiety

How much protein makes sense and how you can read satiety in your own body is covered in how much protein do you need and in satiety as biofeedback. That energy density and growth are not the same thing is shown nicely by the breast milk puzzle.

Eating speed and meal structure

The satiety message from the gut needs time. Anyone who eats very fast is finished with the meal before the message arrives. That sounds banal and is remarkably well backed by data, though only by observational data.

A meta-analysis of 23 epidemiological studies found a mean BMI difference of 1.78 kg/m2 between fast and slow eaters (95 percent confidence interval 1.53 to 2.04) and a pooled odds ratio for obesity of 2.15 (1.84 to 2.51). Heterogeneity between the studies was, however, considerable, and intervention studies were explicitly excluded.

How to read this: [association documented, cause open]. Speed is one of the few starting points that costs nothing and forbids nothing. But no proof follows from these data that eating more slowly changes weight.

The GLP-1 injections: what the approval trials showed and where they belong

No topic in the weight field is so charged. Some see the first real progress in decades, others a shortcut that takes revenge. I find both camps understandable and both too quick.

First the most important point: GLP-1 medications are prescription only. This text contains no dosing for use, no source of supply, no advice to begin and none to stop. What is here is study data and the position of the guideline. Everything beyond that belongs in a medical conversation.

The muscle share, and a figure that circulates wrongly online

On social media you regularly read that 40 percent and more of the weight loss under these medications is muscle. In the current systematic review this figure does not appear as a typical value, it sits at the upper edge of the reported spread. The middle value lies clearly below it.

Covered in detail in GLP-1 injection and muscle loss.

What happened after treatment ended

The same question was tested for tirzepatide with a different design. In SURMOUNT-4, all participants first received the medication open label for 36 weeks and reached minus 20.9 percent on average. Then 670 people were randomised double blind to continuation or placebo. From week 36 to 88, mean weight change was minus 5.5 percent under continued treatment and plus 14.0 percent after the switch to placebo, a difference of minus 19.4 percentage points (95 percent confidence interval minus 21.2 to minus 17.7; P < 0.001). Both studies are to be read independently of each other and not set against one another.

Side effects belong fairly alongside. Nausea, vomiting, diarrhoea and constipation are the most common and occur mainly in the dose escalation phase. Rarer but serious events, and the question of who these medications do not suit, belong in a medical conversation. The cluster has its own article for that: GLP-1 injection: side effects. How the molecule works in the body is covered in the GLP-1 injection and GLP-1, the question of ending treatment in stopping the GLP-1 injection, and the dual receptor approach in Mounjaro and tirzepatide.

When eating becomes a struggle, which diagnostics carry weight, and what remains over years

When eating becomes a struggle

This section deliberately does not sit at the end as a footnote. It sits here because it belongs among the building blocks.

A diet is not a neutral tool. Restriction changes not only calorie intake, but also the relationship with food. And in longitudinal data it predicts exactly what it was supposed to prevent.

How to read this: [transfer limited]. The basic idea that restriction can itself become a risk factor is well established in eating disorder medicine. The concrete figures above apply to adolescents.

And one more point belongs here, because this article lines up so many adjustable parts. A map can turn into an endless list to work through: analysing every night, tracking every curve, checking every meal, leaving out more and more. That is exactly what I want to warn against. When measuring, controlling and avoiding start taking up room in everyday life, that is not progress but a problem of its own, and then the tool goes aside and the topic goes into a conversation. A CGM is a time-limited learning tool and not permanent surveillance, and a list of building blocks is a map and not a set of duties.

A second point belongs to this topic, one the German guideline newly added in 2024: a chapter of its own on stigmatisation. Explicitly because discrimination against people with obesity has increased in society and in the health system. Weight-related stigmatising attitudes are documented among members of various health professions and can influence perception, communication and clinical decisions.

That belongs in a text like this because it sets the tone. Weight is not a question of character. Losing weight is also not a matter of course that one simply has to want. Both are stances I want to avoid here.

Which diagnostics carry weight and which only cost money

This is where functional practice and guideline diverge most clearly. I think both sides deserve a hearing.

The Lancet Commission deserves a paragraph of its own here. 58 experts from several disciplines, among them people with their own experience of obesity, stated that BMI-based measures can both underestimate and overestimate body fat percentage and say too little about health at the individual level. They defined clinical obesity as a state of illness that follows directly from the effect of excess body fat on the function of organs and tissues. That is the international professional world itself stepping away from BMI as the sole verdict.

What a time-limited look at your own blood sugar curve can achieve is described in 14 days with a CGM. As a learning tool, not as diagnostics.

What remains over years

Now comes the most honest figure in the whole field, and it is uncomfortable.

How to read this: [long-term data missing]. Apart from this work there are hardly any robust data over many years for any of the building blocks discussed. For the GLP-1 injections, the longest published courses are considerably shorter than what is intended in practice as long-term therapy. Anyone who tells you they know how it looks in ten years is speculating.

The guideline draws a plain consequence from this: beyond the phase of weight loss, measures for lasting stabilisation should be recommended, and these resemble those of the loss itself. It also states that a new energy equilibrium usually settles in after three to six months, so that maintaining then moves to the foreground.

Frequently asked questions

Where weight connects to the rest of the body

No building block stands alone. Blood sugar hangs on sleep, sleep on the stress axis, the stress axis on the sex hormones, and all of it together on what is on the plate. These articles pick up the individual threads.