Why are two out of three Americans overweight? We're moving less and eating more. Food is cheap, at our fingertips, and calorie-heavy.

Restaurant meals typically have at least 1,000 calories, not including dessert or drinks. Three square meals a day has morphed into two or three feasts sandwiched between several meal-sized snacks.

And we're not even aware of it. Brian Wansink, director of the Food and Brand Lab at the University of Illinois, has spent a career studying what consumers don't notice. The size of a package, the shape of a glass, the words on a menu or label, our proximity to food, and other invisible influences can determine how much of what we eat, according to his research.

Here's how to spot--and sidestep--the eating pressure that slips below the radar.

Brian Wansink is the Julian Simon Research Scholar and Professor of Marketing, of Nutritional Science, and of Agricultural and Consumer Economics at the University of Illinois at Urbana-Champaign. He is director of the University's Food and Brand Lab, foodpsychology.com. He spoke with Nutrition Action's Bonnie Liebman by phone.

Q: Why worry about what makes us eat a few extra calories?
A: If we ate 100 fewer calories each day, instead of gaining 10 pounds at the end of a year, maybe we'd lose 10 pounds. Small factors that we're not even aware of add 100, 200, 400 calories. My studies examine when that happens and when it doesn't.

Q: Don't most people watch what they eat?
A: Many of us are reasonably diligent about what we eat but we don't put that much thought into how much we eat. People may decide to eat Chinese food instead of pizza or fruit instead of potato chips because they're healthier. But once they make that initial choice, they tend to not monitor how much they eat. And a pound of grapes isn't calorie-free.

Q: Do larger portions make us eat more?
A: Yes. We went to movie theaters in Chicago and randomly gave people either medium or really large buckets of popcorn. We found out that the people who were given big buckets ate roughly 50 percent more than the people who were given smaller buckets. But if you asked them to estimate how many ounces or calories they had eaten, there was no difference between what the two groups reported.