Free with today’s Sunday Times, you will find an 80-page GI Guide, the diet that scientists and nutritionists around the world are hailing as the healthiest and most successful route to long-term weight loss. We also have the first of our three-week, pull-out, low-GI eating plans, with delicious recipes.

We are not saying that other diets do not work, they do — if you stick to them. But the point about most diets is that they have built-in flaws, which means that, after a few days, a week or two, or even after six months, most people simply cannot cope with them any longer and return to the old eating habits that made them fat in the first place. This is great for the slimming industry because you become an almost guaranteed repeat customer. It is not so great if you genuinely want to lose weight for good. When you read Style ’s pocket guide, you will learn that following a low-GI style of eating has none of the usual dieting pitfalls, but if you still need convincing, here are some good reasons to choose GI over other diets.

Low fat
Research shows that low-fat eating has a good track record for up to six months. After that, it is really hard to keep low-fat eating palatable and interesting in the long term. Obviously, some people genuinely delight in chomping through endless supplies of rice cakes, but studies show that the yearning for the feel and flavour that fat brings to meals generally gets the better of us.

The GI diet encourages you to eat “good” (ie polyunsaturated and monounsaturated) fats such as olive oil and discourages “bad” (saturated) fats such as those found in butter and fatty meats.

High fibre
The F Plan Diet came out in the 1980s and was a roaring success, partly because, back then, high-fibre foods were pretty straightforward — you ate sugar-free muesli for breakfast, sandwiches made from whole-grain bread for lunch, and pasta or brown rice for dinner. The problem today is that many processed foods, while being able to boast a reasonable roughage content, are also bursting with sugar and fat. A typical 110g flapjack can be labelled high fibre, but can contain 480 calories and 30g of fat. Oat-filled, high-fibre cereal bars may be low in fat, but are often packed with sugar, which sends blood-sugar levels soaring, triggering the release of the hunger-stimulating and fat-storing hormone insulin. Just concentrating on eating high fibre does not take these factors into account.

Fibre is an essential part of a low-GI diet, as its presence slows down the digestive process, which will reduce a food’s GI rating.

High protein, low carb
Wildly successful for the first 14 days, when the total amount of carbohydrate that can be eaten is limited to just 20g a day and weight just falls off. But giving up a whole food group is tough. In this case, it means eschewing all bread, cereals, pasta and rice, avoiding fruit, having just a small serving of broccoli or salad to brighten your plate and existing on high-protein foods such as lean chicken, meat, fish and eggs. Nausea gets the better of some, headaches the better of others and sheer boredom sees others ripping sweets from the hands of minors in a desperate bid for a carbohydrate fix. If you do make it through the initial two weeks, you then move on to a maintenance plan, with carbohydrate intakes rising to between 60g and 100g a day (most of us usually eat about three to four times this). Those who stick to these rules do lose weight and keep it off. However, a lot of people do not do it properly, and slip into a pattern of repeating the first two weeks, stopping, stuffing down the carbs again, doing the first two weeks, stopping, stuffing down the carbs, and so on. This not only sees you losing and gaining the same half-stone, but it is also potentially damaging to your health. After a few months of this pattern, many a high-protein dieter throws in the towel altogether. And even if the proper rules are followed, people fall prey to a new problem: buying manufactured low-carb foods. While low in certain carbohydrates, they are still high in total calories and, when eaten with gay abandon, may actually lead to weight gain.

The GI diet encourages you to devote a quarter of your plate at every meal to protein, as it slows down the digestive process, and a quarter to carbs, which keep you feeling alert and full.

Counting points
Weight Watchers is a slimming club that gets followers to count food as points and go for weekly weigh-ins. On the plus side, lots of people do lose weight initially, because it is very easy to follow, and eating only the number of points the group leader assigns automatically reduces food intake. Some extraordinary stalwarts of the system do follow it for life and keep their weight off. However, many ex-Weight Watcherites I encounter are just normal human beings who are unable to go on ad nauseam seeing a bowl of cereal not as food but as points. They slip off the wagon and pile on the weight. Again. But here is the extraordinary thing: however much weight they have regained, their memory is that Weight Watchers worked and back they trot to counting points and weekly weigh-ins, trapped in this money-spinning merry-go-round of losses and gains.

Thankfully, a low-GI style of eating involves no complicated calculations. All you need to do is use your GI Guide book to check the GI score of the foods you want to eat.

Calorie counting
Even if you carry an encyclopedic knowledge of the calorie content of meals and beverages in your head, in these days of processed foods, hidden calories and confusing labels can catch you out. A ready meal may look low in calories when you read the number it provides per 100g (130 calories per 100g of a spaghetti bolognese ready meal, for instance), but do not forget to multiply it to take account of the serving size you actually eat (a 450g ready-meal serving packs in 585 calories in total). The other problem is knowing how many calories you need to eat in order to lose weight. This usually means that you become obsessed with every morsel you eat, turn into a total diet bore, and eventually get fed up with calorie counting and, once again, give up.

There is no calorie counting per se in the GI diet. However, you do need to keep an eye on portion sizes, as the bigger the portion, the more calories you will be eating.

Times recommends

• It is possible to look stylish while pregnant
• Britain’s tot models
• Who and what benefits from the heat wave?