The Duchess - whose own weight has yo-yoed between nine and 15 stone in the last 10 years - is not alone in her obsession with getting herself - and her daughter - thin. While dieting may be deeply uncool among those in the know, the message has yet to get through to most of Britain, where nearly one third of adults are trying to slim, where 40 per cent of women went on some kind of diet last year - and where the slimming industry reaps a profit of about pounds 1bn annually.
Weight Watchers, which claims it has helped 25 million people lose weight since it was founded nearly 30 years ago, is very much the elderly aunt of the industry, having seen numerous other "miracle" diets - Cambridge and Scarsdale among them - come and go. Its new diet plan, launched last September in a bid to get away from the regimented calorie-counting of the past, includes convenience foods from M&S and Boots sandwiches; the would-be slimmer is allocated a number of points to stick to daily, depending on his or her age, sex, and starting weight. No food is forbidden completely: treats allowed include Tesco's cherry bakewell, Sainsbury's choc ice, a glass of wine and a small bag of tortilla chips. The weekly meeting with a "Weight Watcher leader", and the "weigh-in" (no longer conducted in front of the whole group) are a key part of the Weight Watchers philosophy; the organisation claims it keeps members on the straight and narrow, (although anyone with a pathological aversion to meetings can also follow the WW at-home programme).
Is Weight Watchers a Good Thing? Most nutritionists agree that the organisation is certainly at the more reputable end of the slimming industry and that its advice seems to be sensible. The goal weight decided for each would-be slimmer, for example, is always within recommended guidelines based on the Body Mass Index (BMI); and weight loss (2-3lbs a week at first and then 1.5-2lbs a week) is slow and therefore sustainable, with fat disappearing rather than muscle (although last year Weight Watchers was criticised by the Advertising Standards Authority for using an ad in which one woman lost 8lbs in 14 days).And the new diet, with its stress on plenty of fruit and vegetables and less saturated fat, does appear to promote healthy eating. The organisation also says that it maintains strict rules on children - no members are allowed under the age of 10 and those between the ages of 10 and 16 need parental consent and written permission from their GP before joining.
There seems little doubt that many people are helped to achieve weight loss, at least in the short term: in a randomised controlled trial of about 600 volunteers, published in The Lancet, which compared Weight Watchers with other slimming clubs and other products such as pills, the organisation came out on top, with about 80 per cent most losing about 12-14lbs within a six-week period.
The downside is that although would-be slimmers no longer have to count calories or weigh and measure food, they do have to count how many points they consume each day. According to some dieticians, this type of behaviour leads to an obsession and anxiety surrounding food, especially among women. And most slimming studies show that even if dieting works in the short term, most people who lose weight regain it at some point or another.