Brian Wansink of the University of Illinois at Urbana-Champaign said his research, which involved more than 500 people, indicated a person is more apt to pig out if food is readily plentiful and varied.
Colors also make a major difference. Wansink and Barbara E. Kahn of the University of Pennsylvania found people eat far more jelly beans, or M&Ms, for example, if they are offered in many colors than in just a few.
The multiplicity of colors suggests variety, even if they all taste the same, leads to increased consumption, they said.
What all that suggests, Wansink told ABC, is the "hidden persuaders" that compel us down the road to obesity are "incredibly powerful" and "really, really subtle."