Soft drinks and fast food are not good for the waistline: that would seem to go without saying. So when researchers at two prestigious institutions — Harvard School of Public Health and the University of Navarra in Spain — tracked the consumption of these products among 7,000 people, it came as no surprise that those whose diets contained the highest proportion of “American” foods gained the most weight.

But what was new was the researchers’ conclusion that the weight gain was a reaction to the “decreased satiating quality” of fast foods and soft drinks.

While the glycaemic index is still monopolising the conversations of slimmers, the latest buzzword among weight management experts is satiety — and its measure, the Satiety Index.

At its simplest, satiety is a measure of how long the consumption of a particular food will stop you feeling hungry again. Foods high on the satiety index, such as steak and potatoes, keep hunger pangs at bay longer, while those low on the scale, such as white bread and biscuits, will have you tripping to the pantry sooner.

Satiety involves various mechanisms that influence appetite, with more emerging as the research develops. But it started with data from a very simple set of tests. In 1995 (shortly before the Glycaemic Index was originated) scientists at the University of Sydney ran tests on volunteers to ascertain the satiating effects of a list of common foods. White bread was taken as the median and other foods were scored on their comparative ability to satisfy hunger. The longer a food did so, the higher it ranked.

These were then graded into a Satiety Index, which produced some surprising results, even for the experts: muesli and bananas were no more filling than white bread, while popcorn and oranges were more satiating than cheese or cornflakes. But the results, though enlightening and published in the European Journal of Clinical Nutrition, were not formulated into a diet programme or promoted.

“Obesity was getting to be high on the agenda when we did our original work, and we just weren’t specialists in that area when plenty of people were, so we didn’t pursue or publicise it,” explains Professor Jennie Brand Miller, one of the team of researchers.

Meanwhile GI took off, attracting medical attention primarily because it held promise for treatment of diabetes and heart disease, and SI sat on the backburner.

“It’s surprising that the index was overlooked, given that if you’re dieting — which many people are at any given time — satiety is your key concern,’ says Professor Peter Rogers, a food psychologist at the University of Bristol. “If you don’t feel sated you get hungry and tend to snack or overeat more readily, it’s that simple.”

However, this compelling rationale — and the increasing obesity rates — have sent researchers back to satiety principles, and various satiety-based approaches, inspired by the Sydney data, are now gaining currency.

“Satiety has started to become a buzzword in discussions on obesity,” says Barbara Rolls, Professor of Nutrition at Penn State University. “Glycaemic index is a factor in satiety, but it’s not a reliable measure because it is so variable. It is affected by cooking methods, ripeness of fruit, heat of the food, to name a few. In an experiment (done by Brand Miller and colleagues) the effect of the glycaemic index on satiety was minimal.”

This may explain why the GI and SI rankings of foods — both ostensibly measures of the healthy nutrition — are sometimes contradictory. While the low SI ranking of, for example, peanuts and crisps gives them a nutritional black mark, they score well on the GI measure. Conversely, potatoes, white rice and cornflakes score positively on the SI rating, but negatively on GI.

Rolls suggests that, while the original satiety ratings were not an exact science, they are a better reference point for evaluating foods for weight control than GI. “A compendium of influences affect satiety, but GI is not a major one. With satiety, it’s the energy density and portion size that count.”

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