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Overweight and obesity, explained
Carrying excess weight is a medical condition with a biological cause and recognised medical treatment. This page explains why weight is so much harder to lose and to keep off than willpower alone would suggest, what your waist measurement tells a doctor that the scales do not, and what actually improves in your body when weight comes down — starting from as little as five per cent.
It is not a lack of willpower. It is biology.
Excess weight is a recognised medical condition with a recognised medical treatment. Understanding why it is so hard to lose, and so easy to put back on, is the part most people find genuinely useful — because it explains a great deal that has previously felt like personal failure.
Most people who come to this clinic have lost weight before. Often a great deal of it, more than once. What follows is not a story about effort.
Why doctors treat weight as a medical condition
Not because of how it looks. Because of what it does — and because carrying extra weight around the middle in particular sits at the centre of a cluster of problems that feed one another.
That cluster has a name: metabolic syndrome. It is the combination of excess weight around the abdomen with raised blood pressure, raised blood sugar and disordered cholesterol, and having it raises the risk of type 2 diabetes, heart disease and stroke well beyond what any one of those problems would do alone. The reason it matters clinically is that the components move together — and when weight comes down, they tend to move together in the other direction too.
The effects show up in four broad areas. Metabolically, as insulin resistance, a rising HbA1c, type 2 diabetes, and fat stored in and around the liver — which is reversible and often overlooked. In the cardiovascular system, as raised blood pressure, disordered cholesterol, and increased risk of heart disease and stroke. Mechanically, as load on the knees, hips and lower back, and as obstructive sleep apnoea, breathlessness and the tiredness that follows a night of interrupted sleep. And over the longer term, excess weight is linked to at least thirteen types of cancer, to reduced fertility, and to low mood and a poorer quality of life day to day.
None of this is said to alarm anyone. It is said because the same list read backwards is what improves, and improves fairly quickly, once weight starts to come down.
Where the weight sits matters more than what the scales say
Two people can weigh exactly the same and be at quite different risk. What separates them is usually where the weight is carried — and a tape measure tells a doctor more about that than the scales do.
Fat stored around the abdomen, packed in among the organs, behaves differently from fat stored under the skin on the hips and thighs. It is metabolically active. It is the fat most closely tied to insulin resistance and to raised blood pressure, and it is also the fat that responds first when weight starts to come down — which is why blood results often improve before the difference is obvious in a mirror.
Current UK guidance measures this as a waist-to-height ratio — your waist measurement divided by your height, in whatever units you like, as long as both are the same. NICE classifies a ratio of 0.4 to 0.49 as healthy, with no increased health risks; 0.5 to 0.59 as increased central adiposity, indicating increased health risks; and 0.6 or more as high central adiposity, indicating further increased health risks.
Which comes down to one sentence: keep your waist to less than half your height. It needs no chart and no calculator, it applies to almost everyone, and it is the measure NICE recommends for exactly that reason. Someone 5 ft 8 in tall — 68 inches — is aiming for a waist under 34 inches.
This is also why BMI on its own is a blunt instrument. It cannot tell muscle from fat and it cannot tell where fat sits. It is useful as a starting point and no more, which is why your waist is measured at every assessment here.
BMI thresholds are not the same for everyone, either. NICE advises that people with a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background are prone to central adiposity, and that their cardiometabolic risk occurs at a lower BMI. Lower thresholds therefore apply: overweight from a BMI of 23 rather than 25, and obesity from 27.5 rather than 30. If that applies to you, it is taken into account at your assessment.
Why willpower is the wrong thing to measure yourself against
Your body treats the weight it has reached as the weight it should be, and it defends that level actively. Lose a meaningful amount and a set of changes begins that pushes back — all of them measurable, none of them under conscious control.
The hormones that drive hunger rise. The ones that signal fullness, including the body's own GLP-1, fall. Food occupies more of your attention than it did. At the same time, energy expenditure at rest falls by more than the smaller body alone accounts for, so the same diet that was working stops working. The weight returns — not because effort stopped, but because the pressure to eat rose and the energy used fell, at the same time.
And these changes persist. For a year or more after the weight is lost, not for a few weeks.
What that means is that the hard part is not losing weight. Almost anyone can lose weight. The hard part is that the body responds to having lost it by making it very difficult to keep off — and that response is stronger, not weaker, in people who have more weight to lose.
Medication works on exactly this mechanism rather than around it. It does not remove the need to eat well or to move — it makes doing both possible, by turning down the appetite signalling that would otherwise overwhelm the effort. That is the whole argument for treating weight medically.
What actually changes when weight comes down
Far less than people expect, and far sooner. The number most patients have in their head is the weight they were at twenty-five. The number that changes their health is much smaller than that.
At five per cent of your starting weight, blood pressure begins to fall, blood sugar and HbA1c improve, triglycerides come down, fat stored in the liver reduces, and insulin starts working better.
At ten per cent, all of that more so — and sleep apnoea often improves, knee, hip and back pain eases, the cholesterol profile improves, fertility can improve, and mood and energy usually lift.
At fifteen per cent and beyond, remission of type 2 diabetes becomes a realistic goal for many people whose diabetes is recent, longer-term cardiovascular risk falls meaningfully, and mobility and day-to-day function change noticeably.
For someone weighing 100 kg, five per cent is five kilograms. It is not a transformation and it will not be the number anyone celebrates — but it is enough to move a blood pressure reading and an HbA1c, and those are the things that determine what happens over the next twenty years.
These are the effects seen consistently across weight-management research and reflected in UK clinical guidance. What any individual experiences depends on their starting point, their existing conditions and their medication, and none of it is guaranteed. What is realistic in your case is something to discuss at an assessment rather than to read off a page.
On being told to eat less and move more
Most people who come to this clinic have been given that advice, usually more than once, often by someone who meant well. It is not wrong exactly. It is just an instruction rather than a treatment, and it takes no account of a system that is actively working against the person following it.
The effect of hearing it repeatedly is that people stop asking for help. Research on weight stigma is consistent on this point: people who feel judged about their weight are less likely to attend appointments, less likely to raise it with a clinician, and more likely to put off seeking help for problems unrelated to weight altogether.
Nobody is weighed here to be judged. They are weighed because it is a clinical measurement, like blood pressure, and because it is difficult to treat something you have not measured.
If willpower were the treatment, nobody who had ever tried would still be carrying the weight. Most patients here have more of it than they have ever been given credit for.
Where to go next
Weight loss assessment and treatment — the full pathway.
A detailed consultation, blood tests where they are needed, a plan built around your history, and medication where it is clinically appropriate.
Work out your BMI — a starting point rather than an answer. Useful alongside your waist measurement.
Everything we offer — every route into the clinic, whether you are starting out, already on medication, or thinking about coming off it.
Sources
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NICE. Overweight and obesity management. NICE guideline NG246, January 2025. — waist-to-height ratio classification, BMI categories, and the lower BMI thresholds by family background. nice.org.uk/guidance/ng246
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Cancer Research UK. How does obesity cause cancer? — "Overweight and obesity increases the risk of at least 13 different types of cancer." cancerresearchuk.org/about-cancer/causes-of-cancer/obesity-weight-and-cancer
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Sumithran P, et al. Long-term persistence of hormonal adaptations to weight loss. New England Journal of Medicine, 2011. — the appetite hormones remain altered a full year after weight is lost. doi:10.1056/NEJMoa1105816
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Magkos F, et al. Effects of moderate and subsequent progressive weight loss on metabolic function and adipose tissue biology in humans with obesity. Cell Metabolism, 2016. — 5% weight loss improves multi-organ insulin sensitivity and beta-cell function. doi:10.1016/j.cmet.2016.02.005
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Lean MEJ, et al. Primary care-led weight management for remission of type 2 diabetes (DiRECT): an open-label, cluster-randomised trial. The Lancet, 2018. — remission of type 2 diabetes following substantial weight loss. doi:10.1016/S0140-6736(17)33102-1