While everyone's girth increases with age, a five-year study of 8 000 young Americans found that people tend to pile on even more kilos once they are married.

"Is it the romantic relationship or the shared environment in the household?" asked Penny Gordon-Larsen, one of the authors of the study carried out by the University of Chapel Hill in North Carolina.

Another co-author Nathalie The says there are "several factors, they exercise less, they have children."

The study found that on average over the five years the women in the study gained seven kilos and men 11 kilos.

But those who were married put on more. The women added a further four kilos, bringing their total to 11 kilos and the men gained three kilos extra, for a total of 13.5 kilos.

Nearly 200 million Americans, fully two thirds of the US population,are considered overweight or obese. And Americans' widening girth is responsible for a host of ailments, including diabetes, hypertension and heart disease. Obesity is now the second-leading cause of death across the United States.

"We should try to use the influence couples can have on each other so they can have positive behaviors and support each other to get a healthy lifestyle," said Gordon-Larsen.

The point was driven home in another study of 357 couples where one of the partners was diabetic and following a strict diet and exercise program found that the other spouse also lost weight.

Meanwhile, the conference organized by the Obesity Society, a body of researchers dedicated to ending what has become one of America's most serious health problems, heard that chewing gum can also help control weight.

The study by Glasgow's Caledonian University in Scotland found that "chewing gum suppressed ratings of hunger, desire to eat and cravings for high energy snacks," said one of the authors Marion Hetherington.

Sixty people asked to chew gum as they prepared a meal had fewer hunger pangs and in fact ate less, reducing their sweet snack intake by 46.5 calories, than those who cooked without chewing on any gum, researchers said.

Several studies have found that chewing food also makes you feel fuller. A chopped up apple provides a better snack than apple juice or apple puree, which fail to completely satisfy rumbling tummies.

"Consuming a whole apple, sliced before lunch, reduced total meal energy intake by 15 percent," said Julie Flood, of the study carried out by University Park in Pennsylvania.

Although apple juice or puree contain the same number of calories as an apple, around 152, people offered a meal after consuming a sliced apple ate less than those who drank the juice or spooned up the puree.