Sarah Schenker from the British Nutrition Foundation replies: The two most common artificial sweeteners used in food and drinks are saccharine and aspartame. Saccharine is approved for use in the UK but is banned in the US. According to the World Cancer Research Fund there is a possible link between saccharine and bladder cancer. This has been shown in tests on laboratory rats. Controversy also exists around the use of aspartame. Although it has been approved as safe to add to foods through rigorous testing, some experts aren't convinced and independent trials are underway at King's University to see if there is a possible link with brain tumours.
There are a number of different fat replacers used in foods. These may be protein-based or carbohydrate-based and therefore provide energy. Thus, while the overall calorie content of the food is lowered, some (but not all) of the calories lost by eliminating fat from the product are replaced by the fat substitute.
Energy-free fat replacers are being developed for use in foods. These are neither digested nor absorbed and so contribute no fat or calories to the diet. However, there are potential problems. One such energy-free fat replacer, Olestra, has been withdrawn from use in US after reports that its consumption caused anal leakage, among other unpleasant side-effects.