Many factors influence how much one eats at meals and in between—dim versus bright lighting, background music, boredom, plate size, whether the food is served buffet-style or a la carte, and the list goes on.

Now it turns out even the physical appearance of your dining companions can play a role in what—and how much—you eat. According to an experiment by food psychology researchers from Southern Illinois and Cornell universities in the U.S., you’re more likely to take heaping portions of unhealthy foods in the presence of someone who appears to be overweight.

Researchers had 82 people line up, in eight batches, for a lunch of pasta and salad. Each time, there was an actress at the head of the queue, who drew attention to herself by speaking loudly, then serving herself. Sometimes she took a lot of pasta and less salad. In other instances, she took more salad than pasta. Sometimes she wore a “fat suit,” appearing overweight, and other times she didn’t.

When the actress appeared to be “fat,” regardless of whether she took more pasta or salad, all the other people in line indulged in more pasta. “These results demonstrated that people may eat larger portions of unhealthy food and smaller portions of healthy food when eating with an overweight person,” concluded the researchers, who recently published their findings in the journal Appetite.

The probable explanation for this is that seeing someone who is not the perfect picture of health may “dampen” health-related goals—so an individual who aims to make healthy choices at meals may become less motivated to make those choices upon seeing someone embodying the results of opposite behavior.

This effect has been studied before; a 2011 paper in the Journal of Consumer Research described it this way: “Activation of a negative stereotype (the overweight stereotype) is shown to lead to stereotype-consistent goal commitment (low health goal commitment), which partially explains increases in stereotype-conducive behavior (eating indulgent foods).” That paper cited related studies, saying the same thing, from 2010 and 2007.