Unexplained Weight Gain

Most weight gain comes from taking in a little more energy than you use, day after day, and the gap can be small enough to go unnoticed. The NHS puts it simply: you put on weight when your body turns extra calories from food and drink into fat. A daily snack, a second glass of wine, a desk job after an active one or a few more takeaways a week can each do it.

If you are gaining weight fast, or nothing about your eating or activity has changed, look further. The NHS lists being over 55, perimenopause and menopause, an underactive thyroid, Cushing’s syndrome and certain medicines among the things that make a healthy weight harder to keep. Fluid, poor sleep and stress belong on the list too, and each is covered below.

There is no single cut-off, but the speed tells you a lot about the cause. The British Heart Foundation explains that weight gained through eating habits usually builds over weeks and months, while fluid retention can add as much as 3kg in 1 or 2 days.

So a gain of a few kilograms within days points to fluid, and fluid has a cause that needs finding. The NHS lists sudden weight gain among the symptoms of heart failure and advises an urgent GP appointment or NHS 111 if you have suddenly gained weight.

Gain spread over weeks and months fits the pattern of eating habits, a medicine, sleep or the menopause. A weekly weigh-in and a waist measurement will show its pace.

The causes of weight gain fall into everyday ones and medical ones, and more than one can be at work at once:

• eating and drinking more than your body needs, often in small amounts that add up
• less physical activity than before, through work, injury or a change of routine
• being over 55, as muscle falls and the body uses less energy
• perimenopause and menopause
• an underactive thyroid
• taking some prescription medicines
• fluid retention, from salty food, long spells of sitting or standing, or a heart, kidney or liver problem
• short or disrupted sleep, including sleep apnoea
• stress, through its effect on eating, drinking and sleep
• Cushing’s syndrome, a rare condition caused by too much cortisol

An underactive thyroid causes tiredness and weight gain and is found with a blood test (see thyroid and weight gain). Menopause weight gain often settles around the stomach and upper body (see menopause weight gain).

Some medicines can cause weight gain as a side effect. The NHS lists some prescription medicines among the things that can make it harder to stay a healthy weight.

The clue is timing. If your weight started to climb within weeks or months of starting a new medicine or changing a dose, note the dates and take them to whoever prescribed it. Never stop or change a medicine without speaking to your prescriber first. Many medicines are doing an important job, and your prescriber can weigh the benefit against the side effect and tell you whether anything can change.

Bring a list of everything you take, including anything bought over the counter, to any weight assessment.

Fluid retention adds weight quickly, and it shows as swelling more than as fat. The NHS calls a build-up of fluid in the ankles, feet and legs oedema. It is usually caused by standing or sitting in one position for too long, eating too much salty food, being overweight or thyroid problems, and it can also come from problems with the kidneys, liver or heart.

Signs that extra weight is fluid include puffy ankles, skin that keeps a dent when you press it, and shoes or clothes that suddenly feel tight. A tummy that stays swollen, or keeps growing, needs a GP. The NHS advises an urgent GP appointment or NHS 111 if swelling in your legs comes with swelling elsewhere, such as your face or tummy.

Cortisol is the body’s main stress hormone, and very high levels over a long time cause weight gain directly. That is Cushing’s syndrome, which the NHS describes as rare. Its commonest cause is a prescription medicine taken at high doses for a long time, and its signs are distinctive:

• more fat on the neck, upper back, chest and tummy, with arms and legs that look thin by comparison
• a red, round face
• skin that bruises easily, and stretch marks
• muscle weakness at the top of the arms and legs

If that pattern fits, a GP can check the cortisol in your blood, urine or saliva. Everyday stress works differently. The NHS lists eating too much or too little, sleeping badly and drinking more among the ways stress shows itself, and those habits can move the scales over time.

It can, through its effects on appetite and energy. NHS Tayside notes that adults who do not get enough sleep are more likely to be above a healthy weight, and that lack of sleep increases appetite, especially for foods high in fat and sugar. NHS Better Health adds that poor sleep can leave you too tired to exercise or cook.

Sleep apnoea is worth ruling out if you snore loudly, wake a lot or feel very tired during the day. It is when your breathing stops and starts while you sleep, and the NHS links it to obesity and a large neck. A GP can refer you to a sleep clinic for an overnight test, which you can usually do at home, and losing weight can sometimes treat it.

A standard set of blood tests checks for the medical causes of weight gain that show up in blood:

• thyroid function (TSH and T4), for an underactive thyroid
• HbA1c, for raised blood sugar and prediabetes
• liver and kidney function, because problems with either can cause fluid retention
• a lipid profile, for cholesterol and triglycerides
• a full blood count, as a general check

Cortisol tests for Cushing’s syndrome are arranged by a GP when its signs are present, and sleep apnoea needs an overnight sleep test. Single private blood tests in London cost about £43 to £99 each, and a 22-marker weight panel from OneDayTests costs £125. The terms are explained in the weight management glossary.

See a GP before starting any weight programme if your weight gain comes with any of these:

• weight gain that came on over days or a few weeks
• swelling of the ankles, feet, legs or tummy
• feeling breathless, especially when lying down or during everyday activity
• tiredness, feeling cold and constipation
• more fat on the neck, upper back and tummy with thinner arms and legs
• loud snoring and feeling very tired during the day

If you have swelling and feel short of breath or struggle to breathe, or your chest feels tight, heavy or painful, call 999. If eating or your weight is causing you distress, speak to your GP or contact Beat, the eating disorder charity, on 0808 801 0677.

A first assessment arranged by Medical Weight Loss London at UNTIL Soho starts with the timeline: when the weight came on, what changed around then, every medicine you take and how you sleep. It measures your weight, waist and blood pressure and arranges thyroid function, HbA1c, a lipid profile, liver and kidney function and a full blood count. First assessments at London clinics cost about £150 to £310, with tests on top (what a programme costs).

If the results point to a cause that sits with your GP, the clinician tells you. If they come back clear, a medical weight loss programme builds the plan around what the timeline showed. Ask what to get checked and UNTIL Health Concierge arranges the appointment with a registered clinician.