The sweeteners used in low-calorie food and drinks could pile on the agony for slimmers.
With nearly half of men and more than a third of women officially overweight according to government surveys, so-called “diet” foods and drinks have taken the market by storm.
An extensive range of soft drinks, table-top sweeteners and desserts now comes sweetened not with sugar but with intense sweeteners such as aspartame (NutraSweet), saccharin and acesulfame-K. These sweeteners provide the taste of sugar, or an approximation of it, but almost none of the calories, thus offering the promise of sweetened foods and drinks without adding inches to your waistline.
Yet ironically, a desire for sweet-tasting foods could encourage slimmers to eat more, since the effect of a sweet taste on the human palate, whether in the form of sugar or artificial sweeteners, has been shown to provide a short-term stimulus to the appetite.
In carefully designed studies Drs Peter Rogers and John Blundell at Leeds University compared feelings of hunger and food intakes after volunteers ate samples of yoghurt, either unsweetened, sweetened with saccharin or sugar, or bulked with starch.
Raising the level of sweetness, whether with sugar or with saccharin, increased appetite. However, saccharin had a particularly pronounced effect.
Not only did the saccharin group make up for the calories they would have consumed if the yoghurt had contained added sugar or starch, but they also ate significantly more calories as well on average, a further 200 calories that day. Studies have demonstrated the appetite boosting effect of the taste of the other intense sweeteners.
Why should our appetite respond so strongly to sweetness?
The mechanisms that control hunger and appetite are complex, but Dr Rogers, a research psychologist, explains that the look, smell and taste of food will trigger gastric juices ready for digestion.
A sweet taste seems also to stimulate insulin production, in anticipation of the raised blood glucose levels that would normally follow digestion and absorption of sugar. Without the glucose and calories from sugar digestion, as with foods and drinks sweetened with artificial sweeteners, the body can still be left feeling hungry.
Once swallowed, the effects of intense sweeteners on appetite are less clear. Saccharin, Dr Rogers says, appears to continue to stimulate appetite during its passage through the body, although the mechanisms are not fully understood. Aspartame does not share this physiological effect, and intakes of aspartame by capsule, without taste, were not found, in the Leeds study, to increase hunger, food intake or body weight.
The difficult question to answer is what effect the use of artificial sweeteners has on weight control in the long term. Data on the long-term effects of artificial sweetener consumption on weight control are sparse, according to an American researcher, Dr Barbara Rolls, who reviewed what scientific literature there is in the American Journal of Clinical Nutrition in April this year.
“Intense sweeteners can only be expected to help with weight loss through significant dietary changes to restrict food intake. The substitution of only a few foods may not result in a reduction in daily energy intake,” Dr Rolls concluded.
So it appears that just choosing the “diet” version of your favorite drink, or sprinkling low-calorie sweeteners on your cereals, may not make it any easier to lose weight.
The manufacturer of NutraSweet, the trade name of aspartame, agrees that slimmers need to make more substantial changes if they are to achieve lasting weight loss. “There is an element of correctness in that statement,” says NutraSweet’s Nicola Hyde. But she adds: “Aspartame has never been found to cause weight gain.”
So do claims of “diet” on the label mislead?
Any “diet” product in the UK must carry the proviso that it should be used as part of a calorie-controlled diet. But researchers such as Professor David Booth of Birmingham university argue that brand names, health-orientated tags and advertising slogans such as “diet” or “light” do imply special properties, and many people are likely to believe that such products have advantages for weight reduction.
If slimmers think that “diet” food and drinks will automatically help them to control their calorie intakes, then they are more likely to relax controls and eat more, Dr Rolls argues.
“Artificial sweeteners can be useful, but only if you use them wisely,” Dr Rogers concludes. “Don’t assume diet foods will do the work for you.”