The Cambridge Diet

Introduced in the States after being clinically tested for eight years at Cambridge University, this is a variation on the very low calorie diet (VLCD), which restricts calories to fewer than 500 a day by using complete meal replacements. After four weeks, a switch is made to two replacement meals and an ordinary meal of 400 calories per day.

Verdict: The weight loss can be dramatic, but in almost starving yourself you lose not just fat but muscle as well, which is medically unwise. To lose heart muscle, for example, is potentially fatal. Also, this diet doesn't change long established bad eating patterns.

F Plan

Introduced in the early 1980s, this diet was based on the idea that high fibre foods pass through our system so fast that the body doesn't have a chance to absorb all the calories from it. Hence, the more fibre in our diet, the more calories would be excreted and the greater our weight loss. This diet includes a recipe for a special high fibre muesli, called "fibre filler", which provides 15 g (1/2 ounce) of dietary fibre daily.

Verdict: The F Plan makes everything pass through the body too quickly, thereby reducing the absorption of valuable nutrients.

High protein/no carbohydrate

This kind of diet, popular in the 1970s and enjoying a comeback in America, was based on eating lots of protein, such as meat and eggs, but no carbohydrate, such as bread, pasta, rice or potatoes. Initial weight loss is good up to 6 kg (1 stone) in the first week but, unfortunately, this is made up of water loss, not fat.

When the body is starved of carbohydrates, it looks for energy in its glycogen stores, and because 4 g (0.14oz) of water cling to every gram of glycogen, it is possible to lose a lot of (water) weight very quickly. It is only when the glycogen stores are depleted that the body starts of dissolve the fat. Because this happens slowly, it seems that the diet has stopped working. These protein only diets can cause an abnormal metabolic state called ketosis because there is not enough carbohydrate stored in the liver for the body to use.

Verdict: A difficulty with these high protein ketogenic diets is that they can bring about changes in fat cells, causing them to accumulate even more fat as soon as the person comes off the diet. They have also caused mood changes, such as tension and irritability, resulting in cravings for carbohydrate rich foods and fatty snacks.

Interestingly, when a diet is high in carbohydrates and low in protein, brain serotonin (the "feel good" hormone) levels increase, thereby improving mood and appetite. In a study of 40 obese woman with a long history of yo yo dieting, a diet of 1,4000 calories derived from a high carbohydrate/low protein diet gave them fewer cravings and better overall moods after several weeks, compared to those on the 1,400 calorie high protein/low carbohydrate diet (Obesity, April 4, 1996: 8).

Hip and thigh type diets

These tend to be very low fat, or even sometimes no fat.

Verdict: It is unwise to go on a diet that eliminates essential fatty acids (EFAs), along with saturated fats. The body cannot produce essential fats, so the only source of these is from what we eat. Totally fat free diets have resulted in joint stiffness, skin problems and mood swings.

Marilyn Glenville