As with any type of surgery, a gastrectomy carries a risk of complications. Problems can also occur because of changes in the way you digest food.

Gastrectomies to treat stomach cancer carry a higher risk of complications because most people who have this type of surgery are elderly and often in poor health.

Complications can also occur after a gastrectomy to treat oesophageal cancer. The oesophagus, also called the gullet, is the tube connecting your throat to your stomach.

Possible complications of a gastrectomy include:

• wound infection
• leaking from a join made during surgery
• stricture – where stomach acid leaks up into your oesophagus and causes scarring, leading to the oesophagus becoming narrow and constricted over time
• chest infection
• internal bleeding
• blockage of the small intestine

An infection can usually be treated with antibiotics, but some other complications require further surgery. Before your operation, ask your surgeon to explain the possible risks and how likely they are.

Possible complications of a gastrectomy for obesity include:

• nausea and vomiting – this usually gets better over time
• internal bleeding
• blood clots
• leaking from where the stomach has been closed
• acid reflux – where stomach acid leaks back up into the oesophagus
• infection

It may be possible to treat some complications with medicine, but others may need further surgery. Before your operation, ask your surgeon to explain the possible risks and how likely they are to affect you.

One the stomach's functions is to absorb vitamins – particularly vitamins B12, C and D – from the food you eat.

If your entire stomach has been removed, you may not get all the vitamins your body needs from your diet. This could lead to health conditions such as:

• anaemia
• increased vulnerability to infection
• brittle bones (osteoporosis) and weakened muscles

Changing your diet may help to compensate for your stomach's inability to absorb vitamins. However, you may need vitamin supplements even after changing your diet. The healthcare professionals treating you can advise on this.

Read about recovering from a gastrectomy for more information on diet and supplements.

Immediately after surgery, you may find that even eating a small meal makes you feel uncomfortably full. This could lead to weight loss.

Losing weight may be desirable if you've had a gastrectomy because you're obese, but it can be a health risk if you've been treated for cancer.

Some people who have a gastrectomy regain weight once they have adjusted to the effects of surgery and have changed their diet. But if you continue to lose weight, see a dietitian. They can give you advice on how to gain weight without upsetting your digestive system.

Dumping syndrome is a set of symptoms that can affect people after a gastrectomy. It's caused when particularly sugary or starchy food moves suddenly into your small intestine.

Before a gastrectomy, your stomach digested most of the sugar and starch. However, after surgery, your small intestine has to draw in water from the rest of your body to help break down the food.

The amount of water that enters your small intestine can be as much as 1.5 litres (3 pints). Much of the extra water is taken from your blood, which means you experience a sudden fall in blood pressure. The drop in blood pressure can cause symptoms such as:

• faintness
• sweating
• palpitations
• a need to lie down

The extra water in your small intestine will cause symptoms such as:

• bloating
• rumbling noises
• nausea
• indigestion
• diarrhoea

If you have dumping syndrome, resting for 20 to 45 minutes after eating a meal may help. To ease the symptoms of dumping syndrome:

• eat slowly
• avoid sugary foods – such as cakes, chocolate and sweets
• slowly add more fibre to your diet
• avoid soup and other liquid foods
• eat smaller, more frequent meals

Seek advice from your hospital team or dietitian if you have symptoms of dumping syndrome. For most people, the symptoms improve over time.

After a partial gastrectomy, a small number of people may experience morning vomiting.

Vomiting occurs when bile – a fluid used by the digestive system to break down fats – and digestive juices build up in the first part of your small intestine (duodenum) overnight, before moving into what remains of your stomach.

Because of its reduced size, your stomach is likely to feel uncomfortably full, triggering a vomiting reflex to get rid of the excess fluids and bile.

Taking indigestion medicine, such as aluminium hydroxide, may help to reduce the symptoms of morning vomiting. See a GP if your symptoms are particularly bad.

During a gastrectomy, it's sometimes necessary to cut a nerve called the vagus nerve, causing many people to experience bouts of diarrhoea. The vagus nerve helps to control the movement of food through your digestive system.

Speak to your doctor or nurse if you have diarrhoea, as treatments are available.