WASHINGTON, DC—”Take all you want, but eat all you take,” is an age-old instruction, repeated for generations by cost-conscious parents to their children. It is also, in today’s era of fast, cheap, and calorie-rich foods, a recipe for obesity.
Prevention of obesity requires a careful examination of many attitudes and cultural customs related to food and eating, said Benjamin Caballero, MD, PhD, at a conference on obesity sponsored by the Food and Drug Law Institute.
Obesity is clearly on the rise among children and adolescents, and has been for roughly 20 years. “This is true in every ethnic, racial and demographic group,” said Dr. Caballero, director of the Center for Human Nutrition, Johns Hopkins University, Baltimore. The “causes” of the problem are multifactorial, and include genetic predispositions, widespread availability of high-calorie, low-nutrient foods, and reduced physical activity.
At the core, though, is the question of how the human organism regulates food intake. This, it turns out, is strongly influenced by psychosocial factors.
Somewhere during the transformation from infancy to adolescence, most individuals shift away from regulating intake based on caloric content and toward regulating intake based on volume. This is a profound change, said Dr. Caballero, one that scientists have known about for roughly 30 years. But it is a complex issue, embedded in psychological and cultural factors. Unfortunately, the significance of this change has been largely overlooked.
In a landmark experiment conducted in 1975, Samuel Fomon, a pioneer in infant nutrition research at the University of Iowa, compared the daily formula intake and weight gain in two groups of newborns: those fed low-caloric density formulas versus those fed high-caloric density formulas. The babies showed clear patterns of intake based on energy need. Those receiving the low-density foods ate greater volumes than those on the high-energy density diets, and the amount of weight gained was more or less equivalent between the two groups. This was true for infants between 8 and 41 days old, as well as for those 42 to 111 days old (Fomon SJ, et al. Acta Paediatr Scand. 1975; 64(2): 172–181).
“The babies consumed food based on caloric content,” Dr. Caballero said. “We, humans, can indeed regulate appetite based on energy needs rather than volume. This is an innate capacity.”
In 1998, EA Bell and colleagues, of the Department of Nutrition, Penn State University, studied consumption patterns of adults, who were randomized to low, medium and high caloric density diets for several days. For all three groups, the mean amount of food consumed at meal times as measured by weight, was nearly equivalent for all three groups (Bell EA, et al. Am J Clin Nutr. 1998; 67(3): 412–420). “The curves are super-imposed. The adults consumed the same volumes regardless of caloric density.” However, those individuals on the high-calorie diets were taking in far more calories per meal than those on the low-density diets.
Studies of portion size bear out a similar pattern. Penn State researchers studied eating behaviors among children aged 3–4 and found that these kids consumed, on average, the same total amount of food per meal (by weight) regardless of whether they were given large, medium or small portions. This amount was consistent at around 50 grams per meal.
Adults, on the other hand, tend to finish whatever is on their plates. Among adults, food intake by weight correlates directly with portion size: adults given large portions consume more per meal than those given smaller portions. Those in the large portion group consumed nearly 200 grams more per meal than those given smaller portions.
“We’ve assumed that human beings will automatically eat more food if more food is offered. But this is actually an acquired tendency, something we learn,” said Dr. Caballero. “Somewhere along the way, we shift out of regulation based on energy density to regulation based on volume: the more that is offered, the more we consume. We eat based on external cues rather than energy need.”
In other words, we are not born with eyes bigger than our stomachs; we learn to eat more than we need to. There are many factors that drive this shift, among them the “clean your plate” message that many children receive from their parents. This dynamic is found across cultures and racial groups, and it reflects a mindset based on food scarcity.
For most of our history as a species, food was relatively scarce and precious. The “Waste not, want not,” ethos made complete sense in that context. However, translated into our modern environment, where supplies of calorie-rich foods are easily available and seemingly limitless, the “clear your plate” edict can prove deadly over the long term, especially when it is reinforced by food marketing practices that push a constant “eat more” message.
When working with families in which obesity is a problem, it can be extremely helpful to try and find out a little bit about the family’s perceptions and attitudes about eating, particularly as regards the children. Many families unwittingly encourage their kids to overeat, and few parents understand that children—and humans in general—have the natural capacity to regulate intake based on caloric need.
