At the Institute of Food Research in Norwich, England, food expert Peter Wilde and colleagues are developing foods that slow down the digestive system, which then triggers a signal to the brain that suppresses appetite.
"That fools you into thinking you've eaten far too much when you really haven't," said Wilde. From his studies on fat digestion, he said it should be possible to make foods, from bread to yogurts, that make it easier to diet. While the research is preliminary, Wilde's approach to curbing appetite is one that some doctors say could be key in combating the obesity epidemic.
"Being able to switch off appetite would be a big help for people having trouble losing weight," said Steve Bloom, a professor of investigative medicine at London's Imperial College, who is not connected to Wilde's research.
Controlling appetite a challenge
Scientists in North America and elsewhere in Europe are also trying to control appetite, including through chemical injections or implantable devices that interfere with the digestive system. Bloom said that regulating appetite through modified foods is theoretically possible. Other mechanisms in the body, like cholesterol production, are already routinely tweaked with medicines.
But Bloom warned that controlling appetite may be more challenging. "The body has lots of things to prevent its regulatory mechanisms from being tricked," he said.
For instance, while certain hormones regulate appetite, the brain also relies on nerve receptors in the stomach to detect the presence of food and tell it when the stomach is full.
Wilde's research hinges on the body's mechanisms for digesting fat. Fat normally gets broken down in the first part of the small intestine. When you eat a high-fat meal, however, the body can only digest the fat entirely further down in the intestine. That sparks a release of hormones that suppress appetite.
Wilde's approach copies what happens with a high-fat meal: he coats fat droplets in foods with modified proteins from plants, so it takes longer for the enzymes that break down fat to reach it.
That means that the fat isn't digested until it hits the far reaches of the intestine. At that point, intestinal cells send a signal telling the brain it's full.
Approach similar to diet drugs
Even though the body hasn't had a high-fat meal, it suppresses the appetite as if it has. If the fat had been digested earlier in the intestine, no such signal would be sent. Wilde said the technique should work with any foods that contain fat, like dairy products, pre-cooked sauces, mayonnaise, breads and pastries, and that taste would probably not be affected.
If all goes well, products could be on shelves within a few years, he said. In another technique, scientists at the University of Newcastle have been testing a seaweed extract called alginate that reduces fat absorption by cutting the level of glucose digested by the body before it gets broken down in the large intestine.
That is somewhat similar to how some diet drugs work, such as orlistat, marketed as Xenical by Roche Holding AG, and Alli by GlaxoSmithKline PLC. Orlistat blocks fat absorption, but can result in side effects like gas and diarrhoea. Scientists think that those side effects could be avoided if fibre intake were increased.
In taste tests by several dozen people, participants found that alginate-enhanced bread tasted as good as or even better than regular bread, said molecular physiology professor Jeffrey Pearson, who is leading the Newcastle research.
"It would be very helpful to reduce people's calorific levels by stealth, so they don't notice there's been a change," Pearson said. "People don't want to completely change their lifestyle and stop eating. ... This lets them indulge again."
Concern over control of diet 'magic bullet'
Food companies and pharmaceutical firms are also exploring ways to tinker with appetite. In 2004, Unilever bought the rights to a South African plant traditionally chewed by tribesman to ward off hunger.
A small study found that people given the plant extract, hoodia gordonii, for 15 days, slashed their food intake by 1 000 calories compared to people on a placebo. A Unilever spokesman said the extract would be added to a food or beverage and could hit the market within a few years.
Not all experts are convinced appetite-stopping foods will be a cure-all for obesity. "Humans are a very messy group to control," said Alice H. Lichtenstein, a nutritionist at Tufts University. People are motivated to eat for various reasons, from taste to price to childhood nostalgia, she said.
Other experts worry about how such foods might be regulated once they are available. "If you have this magic bullet, how do you control who gets it? What do you do about anorexics or female adolescents?" asked Peter Fryer, a chemical engineer at the University of Birmingham who also researches modified foods.
But experts agree that foods that cut appetite could be an effective tool against obesity. "Dieting is an awful bore and most human beings are very gullible," Bloom said. "We need all the help science can provide." – (Sapa, October 2008)