Losing weight without trying?
See a GP if you keep losing it. The NHS sets no minimum amount. Most people who get checked don’t have cancer. But your age and sex change what’s likeliest.
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How much weight loss without trying is a worry?
If it keeps going, get it checked. The NHS calls it unintentional weight loss when you lose weight without changing your diet or exercise. It says to see a GP just in case.
Doctors often use a rough line: at least 5% of your usual weight in 6 to 12 months. There’s no agreed definition, so treat it as a guide, not a pass mark.
| Usual weight | 5% is | 10% is |
|---|---|---|
| 50 kg | 2.5 kg | 5 kg |
| 60 kg | 3 kg | 6 kg |
| 70 kg | 3.5 kg | 7 kg |
| 80 kg | 4 kg | 8 kg |
| 90 kg | 4.5 kg | 9 kg |
| 100 kg | 5 kg | 10 kg |
Sources: BMJ Best Practice; NHS
Faster is a bigger sign. Losing 5% to 10% or more over 3 to 6 months is one of the main signs of malnutrition, the NHS says.
Your next step: write down your usual weight and today’s. Our weight loss percentage calculator turns them into a %.
What causes sudden weight loss?
Lots of things. It can be a stressful event, a health condition or a mix of things. The other symptoms you have are the best clue.
Write down every other symptom you notice to show your GP.
| Cause | Examples | Clues to look for |
|---|---|---|
| Stress | Divorce, losing a job, a death | A big change in your life lately. |
| Mental health | Depression, anxiety, eating disorders, obsessive compulsive disorder (OCD) | Depression: low mood that lasts, a change in appetite. |
| Gut problems | Coeliac disease (a reaction to gluten), inflammatory bowel disease (IBD, long-term swelling in the gut) | Diarrhoea, tummy pain, bloating, blood or slime in your poo. |
| Hormones | Overactive thyroid, type 1 diabetes | Thyroid: hungrier than usual, fast heartbeat, hot. Diabetes: peeing more, thirsty, tired. |
| Heart | Heart failure | Out of breath, swollen ankles or legs. |
| Eating less | Poor nutrition, losing your appetite | Eating smaller meals or skipping them. |
| Medicines | Some medicines, such as levothyroxine | Ask your GP or pharmacist. |
| Cancer | Several types | Feeling less hungry, sweating a lot at night, a new lump, unusual bleeding. |
Sources: NHS: weight loss; NHS: depression; NHS: coeliac; NHS: IBD; NHS: thyroid; NHS: type 1 diabetes; NHS: heart failure; NHS: cancer
Eating more but still losing weight? An overactive thyroid often causes weight loss despite a bigger appetite. See overactive thyroid symptoms.
Levothyroxine is a medicine for an underactive thyroid. If you take it, never stop or change a prescribed medicine without your prescriber. Tell your GP about the weight loss instead.
Sudden weight loss in women and men: what’s likeliest?
A UK study followed 70,193 people whose GP noted weight loss. In the first year, fewer than 6 in 100 got any one serious disease.
| Who | Most common diagnosis | Share who got it |
|---|---|---|
| Women under 60 | Depression | 3.74% |
| Women 60 to 79 | Depression | 2.46% |
| Men under 60 | Diabetes | 2.96% |
| Men 80 and over | Cancer | 5.28% |
Source: Nicholson et al, 2022
For cancer, a bigger UK study looked at 326,240 adults. 4.8% were diagnosed with cancer within six months. Of those, 96 in 100 were 50 or over.
Source: Nicholson et al, BMJ 2024
NICE’s line for urgent tests is a 3% cancer risk. Risk was above it for men aged 50 or over and women aged 60 or over.
In younger adults the risk was below 3%. But other symptoms alongside the weight loss raised it enough to need tests.
So a low risk is not no risk. Whatever your age, see your GP and tell them every other symptom.
What tests will my GP do?
What usually happens at the GP
- 1
Questions
Your health, other symptoms and how much you’ve lost.
- 2
Blood tests and checks
UK researchers advise blood tests for diabetes and thyroid problems, and checks on mood and memory.
- 3
Checks by age
50 and over: a poo test (FIT). 40 and over and ever smoked, or with a cough, tiredness, breathlessness, chest pain or less appetite: an urgent chest X-ray.
- 4
If still unexplained
NICE advises urgent tests or a fast-track referral.
Sources: NHS; NICE NG12; Nicholson et al, 2022
FIT is a test on a small poo sample. NICE also says GPs should consider tests for ovarian cancer in women with unexplained weight loss.
Some blood results were linked to cancer in the BMJ study. These were a high CRP (a sign of inflammation) and low albumin (a blood protein). High platelets (cells that help blood clot) or white cells (cells that fight infection) were too.
But no normal blood result on its own ruled out cancer. So if you keep losing weight after normal bloods, go back to your GP. More on the tests: diabetes blood test and thyroid blood test.
What can I do before my appointment?
Six things to bring or do before you see the GP
- Weigh yourself once a week, on the same scale at the same time of day.
- Write down your usual weight and when the loss started.
- List any other symptoms, even ones that seem unrelated.
- List every medicine and supplement you take, and when you started each one.
- Note any big stress lately, like a job loss, divorce or a death.
- If you’re eating less, snack between meals and pick foods and drinks high in calories and protein.
Sources: NHS: weight loss; NHS: malnutrition
The snacking tip is the NHS’s usual first advice for poor nutrition. For ideas, see healthy weight gain foods.
Never stop or change a prescribed medicine without your prescriber.
When to speak to a GP
The NHS says weight loss is not an inevitable part of getting older. Book an appointment if:
- You keep losing weight without changing your diet or exercise. See a GP.
- You have weight loss and other symptoms. See a GP as soon as possible.
- You’ve lost a lot of weight without trying over the last 3 to 6 months. See a GP.
- You’re peeing more, very thirsty, tired and losing weight, and think it’s type 1 diabetes. Ask for an urgent GP appointment or call 111.
- Call 999 or go to A&E if you’re peeing more, very thirsty and tired, and it’s getting worse quickly. The same goes if you also have tummy pain, diarrhoea or sickness, feel sleepy or confused, or breathe faster and deeper. These could be signs of diabetic ketoacidosis (a dangerous build-up of acids in the blood), which can be life threatening if not treated quickly.
Worried about someone else, like an older parent? The NHS says to encourage them to see a GP.