Of parents, children, food, and rats

Two recent research studies in rats have enticed scientists and reporters to speculate about how children learn to eat healthy food. Junk food, rich in sugar and fat, and low-calorie diet foods were both separately shown to “program” young rats to overeat.

Applying diet and appetite research to humans could be a key to our health in the future, because the problems of overeating and low activity levels are continuing to grow throughout the world. Nearly one in four Canadian children are among the estimated 11 million Canadians who are overweight. Because weight affects many aspects of health, public health authorities project a massive increase in health spending due to obesity, unless the trend can be reversed.

Unfortunately, our concern with our waistlines may also have negative consequences for many. Eating disorders, such as binge eating, anorexia, and bulimia, affect about 3% of Canadian women and 0.3% of men at some point during their lives.

Clearly, rodent studies don’t teach us everything we need to know about human food consumption. For instance, many obesity treatments that work well in mice have turned out to be ineffective, dangerous, or unworkable in humans. Still, humans and rats have similar signalling systems that remind us to eat when hungry, and stop eating when full. These systems can even adjust to allow us to eat more or less. We get full more slowly if the nutritional value of the food is low, or when our bodies need more energy due to physical activity, a growth spurt, or pregnancy. Hunger is one face of this signalling network and satiety, the sense of fullness that ends a meal, is the other.

Spoiling your dinner with a pre-meal

Some kinds of foods are designed to mislead our satiety systems, often to help us lose weight. But could such diet foods teach children an unhealthy lesson, disconnecting part of the satiety system?

University of Alberta researchers led by sociologist David Pierce found that diet food taught young rats to distrust the taste of food as a gauge of its calories. Working with colleagues from the departments of psychology, nursing, and nutrition, Pierce fed young rats a diet of low-calorie sweetened or salty gelatin cubes. Then the team used a standard ploy of human and rat diet experiments, the pre-meal.

The pre-meal test is built on the observation that most of us, rats included, will eat less at dinner if we have a snack beforehand. Rats eating regular food followed this rule, but others receiving diet food had learned to distrust the sweet or salty taste of the pre-meal, and went on to consume much more rat chow at the main meal. Young lean rats and a strain prone to obesity both suffered the same overeating problem. However, adolescent rats did not learn to distrust flavours and overeat. The researchers suspect that the older rats trusted their earliest experiences and were not deceived by the low-calorie food.

Professor Pierce’s results could help explain several long term studies in humans that have associated more weight gain with diet soft drinks than the sugary versions.

Low-calorie meals certainly could have a place in the diet of adults trying to lose or maintain weight. But Gail McVey, a researcher at The Hospital for Sick Children and director of the Ontario Community Outreach Program for Eating Disorders, points to research indicating that “low-calorie diet food, eaten for a long period of time, can confuse the cues we use to judge hunger and fullness. This can lead to bouts of unhealthy overeating.” McVey suggests parents focus instead on having the family make and eat a meal together around the dinner table. “The family meal is a great influence,” she says, “It’s fresh, it has variety, and children don’t have the distractions of television or video games.”

Apparently these distractions matter, taking our minds off our meals at the very time we should be noticing how full we are. A study by University of Toronto researcher Nick Bellissimo recently found that boys watching TV ate more than a control group enjoying slices of the same pizza without television.

We may also become confused by other kinds of messages. In California, a study  of children between three and five years old found that they preferred food packaged in McDonald’s wrappers over identical items in plain wrappers. The study did not look at whether the children would eat more of the apparently-branded food, which even included baby carrots presented with the familiar golden logo.

Rat food preferences depend on Mum’s diet

Unlike those baby carrots, many fast foods contain more sugar and fat than our daily meals should. Although seemingly the opposite of diet food, such “junk food” could also teach young palates an unhealthy message. UK researchers from the Royal Veterinary College, led by Dr. Stéphanie Bayol, found that feeding mother rats junk food during pregnancy and breastfeeding led to an increased preference for fats and sugars in their offspring. Junk food here has a typically British meaning, according to the researchers: “doughnuts, muffins, chocolate, crisps, cheese, biscuits and sweets,” were on the menu. From a nutritional point of view, cheese is definitely not junk food, but it is quite rich in fat.

Perhaps the biggest surprise here came after birth. Some rat mothers were switched from the junk diet to nutritionally-balanced rat chow and spent their days nursing the rat pups. When they were weaned, those pups did not have the same strong preference for junk food as the pups whose mothers were still eating the junk diet while lactating. The study authors conclude that a mother’s “nutrition during lactation might play a key role in influencing the long-term appetite of the offspring” for junk food.

Model behaviour

According to McVey from SickKids, children need exposure to a wide variety of foods to grow up with a healthy appreciation for all the food groups. “Families should eat a variety of foods, especially fruits and vegetables. No food group is ‘bad’ -- we all need a balance of fats, carbohydrates, and proteins.” This fall, McVey is convening a meeting of researchers and public health professionals from the fields of obesity and eating disorders. They’ll work towards prevention strategies to halt the growth of obesity without sending the message that everyone should aspire to the same body type or feel ashamed of eating a bowl of ice cream. For now, McVey’s message is to talk less about food, diets, appearance, and weight, while eating more home-made food, more variety, and paying more attention to the little voice from your stomach that says: “I’m getting full.” After all, your children learn to eat by watching you.

Resources

AboutKidsHealth: Nutrition during pregnancy

AboutKidsHealth: Fitness and Nutrition columns

Canada’s Food Guide: http://www.healthcanada.gc.ca/foodguide

The Student Body: Promoting health at any size