The serving-size habits we adapt as children can continue to influence us through our whole lives. This fat-forming transformation in our eating habits happens between the ages of three and five. You can give a three-year-old a lot of food and they will simply eat until they are no longer hungry. They are unaffected by serving size. By age five, however, they will pretty much eat whatever they are given. If they are given a lot, they will eat a lot, and it will even influence their bite-size.
This has been vividly shown by LeAnn Birch at Penn State and Jennifer Fisher at the Baylor Medical School.[i] When they gave three- or five-year-old children either medium-size or large-size servings of macaroni and cheese, the three-year-olds ate the same amount regardless of what size they were given. They ate until they were full, and then they stopped. The five-year-olds, rose to the occasion and ate 26% more when given the bigger servings. This is almost the exact same thing that happens to adults. We let the size of a serving influence how much we eat.
Serving size is a problem at meal time, but it is also a big problem at snack time. What is a healthy-sized snack? Children tend to think that a serving size is open-ended and up for negotiation – it is pretty much whatever food is available and whatever they can weasel out of their parents. If a candy bar comes in a two ounce package, two ounces must be the correct serving. If the candy bar comes in a four ounce package, four ounces must be the correct serving.
How do we adjust serving size to be more reasonable and less negotiable?
One tricky way is to influence how much children believe is still available to eat. If they believe plenty of the snack is available, the serving size is whatever they can argue for, cry for, and negotiate. Suppose you make a peanut butter and jelly sandwich as a snack and give them half of it. Is the serving-size half the sandwich? Not if the other half of the sandwich is still sitting on the counter. At that point, a serving includes anything that is left that can be eaten. What happens if you bought raisins in bulk and gave them a quarter cup of them. The same thing. A quarter of a cup is not a serving – a serving can expand to include is whatever’s left that they want to eat.
If you buy in bulk to save money, you can use the baggy trick. Remember that none of us really seem to know the amount of a “correct” serving size. We typically look at whatever is wrapped or served and we assume that must be one serving. We can use this notion with our children by giving them their snacks not on a plate, but by putting them in a baggie (or even in a small Tupperware container). In this way, when children get it, they believe it is all they are going to get. There is no more, because this was what was in the container. As long as the extras are out of sight, one serving is whatever they were given.
Children look at cues to determine whether they want more to eat. If they think more is available, they can easily think they are still hungry. For instance, in one of our pilot studies, we gave five-year-olds at a day care center six mini-sized cookies in either a zip-lock baggie or on a plate. After they finished the snacks, we asked them if they thought there were any more cookies. Those children who were given cookies on the plate believed that there were more cookies left in the kitchen and they indicated they wanted them. Those children getting the cookies in the baggies were more likely to believe that the cookies were all gone and that snacktime was over.
[i]Many of these classic studies were conducted at the Child Behavior Labs, when both were at the University of Illinois at Urbana-Champaign. LeAnn L. Birch and Jennifer O. Fisher, “Mother's Child-Feeding Practices Influence Daughters' Eating and Weight,” American Journal of Clinical Nutrition, (2000), 71, 1054-61. LeAnn L. Birch, Linda McPhee, B. C. Shoba, Lois Steinberg, and Ruth. Krehbiel, “Clean up Your Plate: Effects of Child Feeding Practices on the Conditioning of Meal Size,” Learning and Motivation, (1987), 18, 301-317. See also Barbara J. Rolls, Dianne Engell, and LeAnn L. Birch, “Serving Portion Size Influences 5-Year-Old but Not 3-Year-Old Children's Food Intakes,” (2000), 100, 232-234. Jennifer O. Fisher, Barbara J. Rolls and LeAnne L. Birch, “Children’s Bite Size and Intake of an Entrée are Greater with Large Portions Than with Age-Appropriate or Self-Selected Portions,” American Journal of Clinical Nutrition(2003), 77, 1164-1170.
For 30 years my Lab and I have focused on discovering secret answers to help people live better lives. Some of these relate to health and happiness (and often to food). Please share whatever you find useful.
This video of one of my post-docs gives a flavor of one type of research that we've done: