Law of Demand and Diets

Conventional diets often advice keeping food in the pantry, instead of a bedroom. According to the third law of demand, you might actually end up eating more when snacks stay out of easy reach.

The third law of demand states that adding a fixed cost to an action lowers the relative cost of the higher-cost action. The quantity demanded of high-quality goods relative to low-quality goods will increase. Higher quality snacks are snacks that carry higher costs, in health benefit terms (not monetary). They are generally higher in sugar content, calories, or sodium. Eating these snacks imposes a higher cost on health outcomes than more nutritious alternatives.

Fixed Cost on Snacking

Storing food in a pantry adds a fixed cost to snacking. Getting off the couch and ambling into the pantry imposes a fixed cost. All things held equal, you would eat more when you have to put in more effort to acquire the same snack. Personally, if I have to walk out of my room and down the stairs to get chocolate truffles, I’m more likely to eat larger quantities in one sitting. Going downstairs involves more effort (can you tell that I’m lazy?). If I have self-control and discipline, I would eat fewer chocolate truffles if I kept them in my room.

Other theories that may explain why people eat more when food is kept in the pantry rely on biology and psychology. Perhaps they associate the pantry with food, the brain sends a signal to make them feel hungrier. This theory only applies on the margin, removing lack of self-control and biology/psychology as potential confounding factors.

Fixed Cost of “Breaking a Diet”

The third law of demand can also be applied to binge eating. Once the diet is broken, the relative cost of eating a marginal unit of food is minuscule. Breaking the diet imposes a giant fixed cost, at least a subjective one. After the first bite or portion, the cost between eating more and less is negligible. As more units are preferred to fewer, one would eat more food. Thus, one ends up enjoying a larger quantity of food than they would have without restricting food consumption.

If you have good self-control, perhaps you should keep food in your room to enjoy all things in moderation.