If you don't believe me [[http://www.nhs.uk/chq/pages/1862.aspx?CategoryID=51&SubCategoryID=164 here is some info from the NHS website.
Some extracts...
"A food with a high GI will produce a sudden rush in blood sugar, while a food with a low GI will keep your blood sugar levels more stable.
Eating low GI foods will leave you feeling fuller for longer, and will help you to avoid snacking in between meals. Foods that have a low GI include:
apples,
oranges,
pears,
porridge,
beans,
peas,
pulses,
lentils,
bran cereals, and
peanuts.
However, as well as eating low GI foods, sometimes it is necessary to eat high GI foods. For example, after exercising your muscles need to restore their sugar levels quickly, as most of their energy will have been used up. This is when eating a food with a higher GI value, such as a banana, can be beneficial."
Hmm a banana - not a piece of chocolate!
"Fats are divided into two groups - saturated and unsaturated. Eating a small amount of unsaturated fat will help to keep your immune system healthy and can reduce cholesterol levels.
Foods that are high in sugar, such as chocolate, cakes, biscuits, and fizzy drinks, give your body an instant energy rush when you eat them. However, after the initial rush, your sugar levels will drop. As your sugar levels drop, so will your energy levels. As a result, you may find it more difficult to concentrate, or you may feel irritable, tired, and lethargic. As sugary foods are bad for your teeth and high in calories, you should eat them sparingly, as a special treat."