Poor appetite and loss of appetite: causes, red flags and when to seek help

Appetite is controlled by hormones, the gut, the brain and the senses of taste and smell. It dips with almost any illness, because chemical messengers released during infection act on the brain to switch hunger off. That short-lived change is helpful and harmless. A persistent loss of appetite is different, and it matters to distinguish three experiences: not wanting food at all, feeling full after a few mouthfuls, and wanting to eat but being unable because of nausea, pain or difficulty swallowing.

Poor appetite is also not the same as the eating disorder anorexia nervosa, in which a person restricts food because of fear of weight gain. The symptom described here is a loss of the wish to eat, and the two need quite different approaches.

Short-term causes are the commonest: viral and bacterial infections, a stomach bug, constipation, dental or mouth pain, and the effects of heat. Longer-lasting loss of appetite comes from a wider set of causes.

The NHS lung cancer symptoms page lists a cough that is not going away, shortness of breath, coughing up blood, chest or shoulder pain, repeated chest infections, losing weight without trying, not feeling hungry (loss of appetite) and feeling tired all the time. The oesophageal cancer page lists problems swallowing, feeling or being sick, heartburn or acid reflux, indigestion, a cough that is not getting better, a hoarse voice, loss of appetite or losing weight without trying, feeling tired or having no energy and pain in the throat or middle of the chest. The bowel cancer page lists changes in poo, blood in the poo, tummy pain, a lump in the tummy, bloating, losing weight without trying and feeling very tired or short of breath.

Each of these pages stresses that the symptoms are common and can be caused by other conditions, so having them does not definitely mean cancer, but it is important to get them checked, since finding cancer early may make it easier to treat.

The NHS describes the main symptom of malnutrition as unintentional weight loss, though this is not always obvious. It says you could be malnourished if you unintentionally lose 5 to 10% of your body weight within 3 to 6 months, if your BMI is under 18.5 (and a person with a BMI under 20 could also be at risk), or if clothes, belts and jewellery seem to become looser over time. Other symptoms include reduced appetite, lack of interest in food and drink, feeling tired all the time, feeling weaker, getting ill often and taking a long time to recover, wounds taking a long time to heal, poor concentration, feeling cold most of the time and low mood.

In children it can show as not growing or putting on weight at the expected rate, behaviour changes and low energy. If a friend or relative has lost a lot of weight, the NHS encourages talking to them about your concerns and urging them to get help.

See a GP promptly for appetite loss that has lasted more than a couple of weeks, any unintentional weight loss, difficulty swallowing, vomiting that persists, black or bloody stools, drenching night sweats, a lump, jaundice or severe tiredness. The NHS says to see a GP if you have unintentionally lost a lot of weight over the past few months. The NHS oesophageal cancer page says to ask for an urgent GP appointment or get help from NHS 111 if you are being sick for more than 2 days or your poo is black or dark red.

Seek emergency help if loss of appetite comes with confusion, severe abdominal pain, repeated vomiting that stops you keeping any fluid down, signs of severe dehydration or, in a person with diabetes, vomiting. A sudden loss of appetite with severe low mood or thoughts of self-harm needs urgent mental health support.

The doctor will ask how long appetite has been poor, how much weight you have lost and over what time, whether food feels unappealing, you fill up quickly or swallowing is difficult, what you eat in a day, mood and sleep, medicines, alcohol, smoking, and any pain, bowel changes, cough or fever. They will weigh you and calculate BMI, check for dehydration, pallor, jaundice, thyroid enlargement, lumps and mouth problems, and examine the abdomen and chest.

Common first tests are blood tests including full blood count, kidney, liver and thyroid function, glucose, inflammatory markers and coeliac screening, a urine test and sometimes a chest X-ray. Further tests such as endoscopy, scans or a stool test follow the clues.

Little and often usually works better than three big meals. Small snacks or nourishing drinks between meals, favourite foods when you feel able, adding milk powder, butter or cream to meals, and eating when your appetite is at its best, often the morning, help to maintain weight. Gentle activity, fresh air and sharing meals can stimulate appetite. Look after your mouth, since dental or mouth pain reduces eating. A dietitian can provide a personalised plan and prescribe fortified drinks where needed.