Poor old mangoes and grapes are being left on the shelves as dieters follow the new glycaemic index (GI) diet. Six of the top ten diet books now have the term “GI” in the title, pushing Mr Atkins out of the picture — along with the British subsidiary of the Atkins corporation, the producer of its food range, which announced its closure this week.

GI concentrates on a distinction between “good” and “bad” carbohydrates. But I prefer a new diet based on glycaemic load (GL) — a more sophisticated take on the GI diet — which may soon take its place. In the GI diet “good” carbohydrates such as oats are digested slowly, so providing your body with a steady supply of blood sugar throughout the day. “Bad” carbs, such as the fruits mentioned above, are rapidly digested, causing a quick surge of blood sugar and then of insulin, a hormone which controls the amount of sugar in the blood. The better controlled our blood-sugar levels, the less likely we are to experience reactive hypoglycaemia — when blood-sugar levels fall below normal after a high GI food hit has produced a lot of insulin.

For me, a previous sufferer from panic attacks, this imbalance can trigger unpleasant symptoms: sweating, poor concentration, lethargy, palpitations and feeling weak. When I stay away from “bad” carbs I feel more alert and satiated, so it reduces cravings for more “bad” carbs.

Insulin also promotes the storage, in fat cells, of fatty acids from the blood, so overloading on “bad” carbs can lead to weight gain and ultimately to type 2 diabetes and heart disease. The GI diet also creates an internal body biochemistry that encourages fat burning. It is based on excellent science that has been well respected by nutritionists and doctors for decades, especially with regard to diabetes. However, I have reservations about its scoring system having such a strict effect on food choice.

Foods are rated between 1 and 100 in the GI diet. You are advised to eat foods rated with low numbers — ie, below 50 which are the slowly absorbed carbs — and to avoid those rated over 70 where the carbs are absorbed quickly. Mangoes and grapes are above the 50 cut-off point and although many of the GI diet books say people should not stop eating them because they’ re high in important nutrients — vitamin C, beta-carotene and potassium — I’m sure people do.

The GI value tells you only how rapidly your body converts a carbohydrate to sugar; it doesn’t tell you the quantity of that carbohydrate in a serving of a food. You need to know both to understand a food’s effect on blood sugar. This is why I’m also a fan of the new GL diet, the next big thing, which takes into account the quantity of carbohydrate in a food.

Take two classic foods — carrots and chocolate. On the GI scale they both score a “just healthy” 48. However, GL has a different index, with foods scoring 10 or under being good, and 20 or more being bad. It rates the carrots as a good 3.9 and chocolate a nearly bad 14. This is because although both contain carbohydrates that are digested fairly quickly, you’d have to eat at least two carrots to provide the same amount of fast-releasing carbs you’d get in two squares of chocolate. It is this difference that GL factors in.

It means foods which would be off-limits in the GI diet are fine in GL, such as apricots which rate a high 57 in GI but a healthy 4.9 in the GL.

Give it a try, because unlike many food fads, both these diets can help you to achieve your health goal.

Remember the weight loss a well-balanced GL or GI lifestyle can bring will be much slower than high-protein Atkins-type diets. The weight should stay off — unlike high-protein diets, where as soon as you give up on the bacon breakfasts it can pile back on again.

The GL diet is so new that there aren’t any diet books on it yet, but for an up-to-date list of GI and GL values, see glycemicindex.com.

Jane Clarke answers your questions in T2 on Tuesdays. Send e-mails to Jane.Clarke@thetimes.co.uk; www.janeclarke.com Jane cannot enter into personal correspondence

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