A.  Chitosan (pronounced KITE-oh-zan) is a type of dietary fibre. It and its precursor chitin have been hailed as 'fat binders' with the power to soak up fat and get rid of it – an instant appeal for anyone struggling to lose weight.

Ads often show a beaker of oil with chitosan being mixed in and then forming 'clumps' of fat – the idea is that it does the same thing in your digestive tract.

The ads claim that the chitosan acts like a 'fat sponge', soaking up any dietary fat consumed which is then excreted via the bowel. If only that were vaguely true!

A 2005 trial of the weight-loss supplement on 24 men and women in the USA was the fifth study to reach the conclusion that chitosan does not work. The volunteers were fed 2.5 grams of chitosan a day (10 capsules) and the researchers detected a mere 1.8 grams of extra fat excreted in the men and no difference in the women.

The researchers concluded that chitosan was a waste of money.

Even if it did work, chitosan could only 'mop up' so much fat. In the laboratory, a gram of chitosan can bind around 3 grams of fat. But with average fat intake somewhere between 80 to 100 grams a day, the amount of fat trapped would be too small to make any difference to fat excretion.

The bottom line

You still need to eat less and do some regular exercise such as walking or swimming. You certainly won't see any results if you don't.