Unexplained Weight Gain

Medication — look here first

This is the commonest identifiable cause and the one most often overlooked, because people are rarely warned:

• Antipsychotics — olanzapine and quetiapine in particular, where gain can be substantial
• Antidepressants — mirtazapine and amitriptyline notably; some SSRIs over longer periods
• Diabetes medication — insulin, sulfonylureas such as gliclazide, and pioglitazone. Worth knowing that other diabetes drugs cause weight loss, so the choice may be revisitable
• Oral steroids, which cause both fluid retention and appetite increase
• Gabapentin and pregabalin
• Beta blockers, through reduced energy expenditure
• Some hormonal contraception, mainly through fluid rather than fat

Hormonal causes

• Underactive thyroid — commonly blamed and genuinely responsible for a modest amount, typically a few kilograms, much of it fluid. Easy to test, easy to treat
• PCOS — insulin resistance makes weight gain easier and loss harder
• The menopause — falling oestrogen shifts fat distribution towards the abdomen and reduces muscle mass, so the same habits produce a different result
• Cushing's syndrome — uncommon, but the pattern is distinctive

Fluid rather than fat

Rapid gain over days is fluid. Causes include heart failure, kidney disease, liver disease, and medication including steroids, some blood pressure drugs and NSAIDs. This needs assessing rather than dieting.

Other

• Short sleep and sleep apnoea, both of which raise hunger hormones
• Stopping smoking — typically 4 to 5kg, which is a real effect and still an overwhelmingly worthwhile trade
• Alcohol; reduced activity after injury or illness; and binge eating disorder, which is common, treatable, and rarely volunteered

The purpose of assessment is to separate the small group with an identifiable, treatable cause from the larger group who need weight management — and to make sure a medication effect is not being missed.

The history does most of the work

• Speed and timing — how much, over how long, and what else changed at that point
• A complete medication review, including anything started in the previous six months. This is where the answer most often is
• Diet, activity, alcohol and sleep
• Menstrual pattern, mood, and eating pattern including bingeing
• Snoring and daytime sleepiness

Blood tests

• Thyroid function — the first test in unexplained weight gain
• HbA1c, for diabetes and insulin resistance
• Liver and kidney function, particularly where there is any swelling
• Female hormone profile and testosterone where PCOS is suspected
• Lipids, and a full blood count
• Cortisol testing only where the specific pattern of Cushing's is present — it is not a routine test and produces misleading results when done without indication

Our weight and metabolic panel covers the core set in one visit.

A note on expectations

In the large majority of people, these tests come back normal. That is not a wasted exercise — it excludes the treatable causes properly, and it means the plan can move on to what will actually work rather than leaving a nagging question about the thyroid.

Before your appointment

• Bring a list of every medication, including anything started in the last six months, plus supplements and anything bought over the counter
• Note roughly how much weight, over what period — old photographs or a previous weight from a record are more accurate than memory
• Note any other symptoms, even ones that seem unrelated — cold intolerance, hair changes, periods, mood, snoring

Things worth doing while you wait for results

• Prioritise sleep — seven hours or more. Short sleep raises hunger hormones and undermines everything else
• Protein at every meal, which reduces hunger and protects muscle
• Resistance exercise twice a week. Muscle is metabolically active, and preserving it protects your metabolic rate
• Reduce alcohol — calorie-dense, and it lowers restraint
• Keep a brief food and drink record for a week. Most people under-estimate intake substantially, and this is how memory works rather than dishonesty

What not to do

• Do not stop prescribed medication because you suspect it is causing weight gain. Raise it — particularly with psychiatric medication, where stopping abruptly carries real risk
• Avoid very low calorie diets without supervision, which cost muscle and are followed by regain
• Detoxes, cleanses and fat-burning supplements do not work. Some are harmful
• Do not weigh daily and react to each reading — weekly is more informative

Is my thyroid to blame?

It is worth testing, and it is the first test we do — but expectations should be realistic. An underactive thyroid typically accounts for a few kilograms, much of it fluid, rather than a large gain. Correcting it returns that amount and no more. It is checked because it is easy, treatable and important, not because it usually explains everything.

Could my medication be doing it?

Very possibly, and this is the most frequently missed cause. Several antipsychotics, antidepressants, diabetes drugs, steroids, gabapentin, pregabalin and beta blockers all cause meaningful gain. If it started within weeks of a new prescription, that is the first thing to examine — but do not stop anything before discussing it.

I have gained 3kg in four days. How?

Not as fat — that is physiologically impossible over four days. Rapid gain is fluid, and it points to the heart, kidneys, liver or a medication rather than to diet. It should be assessed rather than dieted away.

Why has my weight changed since the menopause?

Falling oestrogen shifts where fat is stored, towards the abdomen, and muscle mass declines with age unless actively maintained. The result is that the same eating and activity produce a different outcome. Resistance training and protein intake matter more after the menopause than before, and HRT may help with the distribution though it is not a weight-loss treatment.

I stopped smoking and gained weight. Should I start again?

No. The average gain after stopping is around 4 to 5kg and it is real — nicotine suppresses appetite and raises metabolic rate. But the health gain from stopping vastly outweighs the weight gained, and the weight can be addressed afterwards. Never trade one for the other.

My tests were all normal. What now?

Normal tests are useful — they exclude the treatable causes properly. What follows is weight management with realistic goals, and medication if you meet the criteria. Normal tests do not mean nothing can be done; they mean the plan can proceed without an unanswered question hanging over it.

Am I just eating too much?

Almost everyone under-estimates their intake, which is a feature of memory rather than a character flaw. But the more useful question is why appetite is where it is — sleep, medication, hormones, stress and eating behaviour all shift it, and those are addressable in a way that being told to eat less is not.

Should I try a detox or a fat burner?

No. Neither has credible evidence, some contain undeclared or harmful ingredients, and the money is better spent on something that works.