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Take a moment and eat less, even when you're hungry
So many factors outside of ourselves can influence what we eat, when, and how much. Just having snacks around can make you want to eat them (Bite, 9/18/13), and using larger plates or bowls can lead you to eat more, even if you know better (Bite, 10/06/06), the food isn't very good, or you're not even hungry.

Hunger, Blood Glucose, and the Glycemic Index
We don't exactly know how the feeling of hunger is caused in the body. One theory, first formulated in the 1950's, is that low levels of glucose in the brain are a cause of the feeling of hunger and the increase in appetite that goes along with it. More recent theories expand on that theory by speculating that it's the changes in blood glucose levels that lead to the feeling of hunger. 

Appetite and chewing gum
Large-scale, long term studies of total daily food intake show that between 1977 and 1994 the average American's food intake each day increased by about 200 calories. Most of this was in snacking, not regular meals. Other studies indicate that the more often a person eats, the more likely they are to consume more calories than they require and to risk overweight.


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Grocery Shopping While Hungry

Man choosing fruit at a grocery store

You've probably noticed that it's not a good idea to go grocery shopping when you're hungry. It's all too easy to end up buying a whole bunch of things you didn't plan on buying just because it looked good and you were hungry.

Brain scans of people who have been fasting (i.e., are hungry) and are shown pictures of high calorie foods show higher levels of brain activity in those areas of the brain associated with reward. This isn't the case with lower calorie foods, however. Brian Wansink and his colleagues at Cornell University noted this and wondered if shopping while hungry meant buying more food in general, or if people tended to buy higher calorie foods. They performed two studies, one in the lab and one in the field (JAMA Intern Med 2013;173(12):1146-1148).

In the first study, nearly 70 men and women were instructed to avoid eating for five hours before participating in a study in the lab. A randomly chosen half of the participants received a snack of Wheat Thins upon arrival, while the other half did not (so they remained hungry). Then they were asked to shop in a simulated online grocery store in which a higher-calorie item was displayed next to a lower-calorie item.

In the second study the researchers went to a local grocery store and tracked the purchases of over 80 people. Half of the people tracked were shopping when people are less likely to be hungry (between 1pm and 4pm) and half were shopping between 4pm and 7pm, when people are more likely to be hungry.

In the case of the online grocery store, the research team found that people bought about the same number of items whether they were hungry or not. However, those who were hungry bought more higher-calorie items - almost twice as many higher-calorie items than those who were not hungry.

In the real grocery store, those shopping in the early afternoon, when they were not hungry, bought 4 times as many low-calorie items than high-calorie items. Shopping in the evening, however, led people to purchase more high-calorie items, bringing the ratio of low-calorie to high-calorie foods to about 2 and a half.

What this means for you

If you must shop when you're hungry, think ahead and make a list. Then stick to it. Better yet, have a snack beforehand (a piece of fruit or some nuts). The best option, of course, is planning all your meals for the week. You can then do all your grocery shopping on one day, list in hand, and avoid the hazards of shopping while hungry completely.

First posted: May 8, 2013