Certainly what we eat affects our weight.

Certainly what we eat affects our weight.

But researchers are finding that when we eat, and with whom, can also have a major impact on our accumulation of pounds.

First there's the timing of meals.

One study, reported recently by scientists at Northwestern University in Chicago, suggests that calories consumed late at night tend to hang around as fat.

They looked at two groups of mice over a six-week period. Both sets of animals were fed the same high-fat diet and got the same level of activity, but one was fed at times when the mice would normally be asleep.

And that group put on twice as much weight as those fed during waking hours.

A number of recent studies have suggested that the body's natural internal clock, whose works include hormones that regulate sleep and appetite, plays a role in how the body uses energy.

Researchers have noted that people with disrupted sleep cycles, like shift workers and college students pulling all-nighters, tend to eat at odd times and often become overweight as a result.

"How or why a person gains weight is very complicated, but it is clearly not just calories in and calories out," said Fred Turek, of Northwestern's Center for Sleep and Circadian Biology. "Better timing of meals could be a critical element in slowing the ever-increasing incidence of obesity."

Along with not eating too late, Barbara Fiese of the University of Illinois-Urbana says in a new report that eating together is crucial both for nutritional and emotional health.

"There are few things that parents can do that are as effective in protecting their families as taking 18 to 20 minutes to eat together and talk with each other three to five times a week," Fiese said.

In a report published in a recent issue of the journal Social Policy Report, Fiese and Yale University's Marlene Schwartz make the case that it should be a matter of public policy at all levels of government to encourage family mealtime.

They note that other research has shown that meals prepared at home tend to be lower in calories and fat than meals eaten out, while shared mealtimes protect children against obesity and older children against eating disorders.

Yet everything from school schedules to local zoning laws to food-labeling laws combine to make it hard for families to eat healthful food at home together.

"Most people don't think of family mealtimes as a policy issue — they think of them as private events," Fiese said. "But sometimes policymakers work against the best interests of families."

Another obesity researcher, Edward Abramson of California State University, Chico, notes that parents improve the odds of kids eating more healthful foods if they see them enjoying the food at home and are involved in preparing it.

"If the child is in the kitchen cooking with Mom or Dad, it's unlikely that he or she will refuse the food they've helped prepare," he said.

Other research shows that the parent-food connection goes back even to the womb.

Rodent studies have shown that when mother rats eat high-fat diets, it produces brain changes in their offspring that stimulates the appetite.

More telling is a study in women who had undergone weight-loss surgery between pregnancies — specifically, a surgery that makes the stomach smaller and bypasses food around part of the small intestine, resulting in less calorie absorption.

The researchers, from New York and Canada, found that children born to the women after the surgery had reduced birth weight and waist circumference and were three times less likely to become severely obese than those born to the women before the operation.

In addition, kids born after the weight-reduction procedure had reduced risk factors for heart disease, such as less insulin resistance and lower cholesterol levels.