People generally know how much they should eat. Yet, even people with very good nutritional habits can be susceptible to the trap of overeating. In a culture full of diet fads and "thinner thighs in three weeks," a new book, Mindless Eating, by Dr. Brian Wansink of Cornell University, is actually a worthwhile read. Wansink and his colleagues have spent years trying to elucidate the reasons why people do not eat the way they should—or even the way they want to.

A common belief is that with proper education people can be taught to make good, healthy choices. Dr. Wansink's team suggests that education about food is not as effective as changing habits and environment. They studied how plate or bowl size influence portion control—larger container sizes lead to higher caloric intake. This is true for the dinner plates in the kitchen cupboard and for the bowls that movie theater popcorn is served in. It is also true for packets of snacks. In fact, this group was instrumental in the invention of the now ubiquitous "100-calorie packs" available at every grocery store.

One of their most revelatory experiments involved monitoring the snacks eaten by a group of Cornell University graduate students, overall an unusually intelligent and well-educated group. They attended a lecture by Dr. Wansink that centered on how the size of a snack bowl would influence the amount of snacks eaten. It was a very academic presentation, 90 minutes of statistics correlating bowl size to number of calories consumed and explanations on how people could avoid such overeating traps. A couple of weeks later, these same students were invited to a football-watching party. Two rooms were set up for viewing, and one room had small bowls of snacks while the other room had larger bowls of the same snack food. Even after being specifically educated as to the effect of bowl size, the students in the big-bowl room consumed, on average, 53 percent more snacks than those in the small-bowl room. Furthermore, when these randomly selected big-bowl students were asked about why they ate so much, each one had an excuse independent of the availability of the snacks. Rather, they claimed they ate more because they had skipped a meal or were extra hungry.

These researchers also found that people who eat at McDonalds underestimate the calories they consumed in a given meal by about 19 percent. However, people who eat at Subway (considered to provide healthy fast food) underestimated their caloric consumption by 27 percent. They also found that people will eat about 20 percent more calories of a food labeled "organic" than the same conventional food. Organic by no means implies low calorie, but the healthful image seems like a license to overeat.

Some very simple strategies can be employed to discourage overeating. The researchers tested how much candy would be eaten from a workplace desk if the candy bowl was either transparent or opaque, and if it was placed either on the desk or across the office, six feet away. Over the course of a year, people whose candy was placed six feet away in an opaque bowl consumed 125 fewer calories per day. If everything else stays the same, that expands to about 11 pounds per year.

Another phenomenon these researchers studied is how exercise can sometimes lead to weight gain instead of loss. Most people don't have a realistic understanding of the caloric value of food and how many calories get burned off by exercise. A clever experiment involved telling conference attendees that their dinner was delayed and so they would be taken on a mile walk around the campus. One group was led by a staffer who kept exhorting them to keep up a brisk pace and monitor their heart rates. The other was led by a staffer who pointed out historical sites. Both groups actually walked at the same pace. Once dinner was served, those who thought they had been on an exercise walk consumed more calories overall and specifically asked for dessert more than did the people on the history walk. They felt entitled to a reward. The others did not feel entitled because they were not told that they were exercising. It should be noted that people who exercise regularly seem to have a more realistic understanding for this input/output relationship.

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