Study after study has shown that the more people have on their plates -- or in their bags of chips or boxes of popcorn -- the more they're likely to eat. Even the size of a plate (or bowl or spoon) can influence how much people eat. For example, in a study reported by Brian Wansink, then a food psychology professor at Cornell University, in his 2006 book "Mindless Eating," people served themselves more on a bigger plate than on a smaller one. In another study led by Wansink and published in the American Journal of Preventive Medicine in the same year, 85 nutrition experts served themselves more ice cream when given a larger bowl and spoon than when given a smaller bowl and spoon -- and most of them proceeded to eat the full portion.
Not all research in this area points in the same direction, however. Rolls, for example, led a team that found plate size did not influence how much people actually ate whether food was served to them or they served themselves.
The study, published in the journal Appetite in 2007, also found that when people served themselves from a buffet, the ones who were given the smallest plate went back for refills more often than those with bigger plates.
In general, portion-control plates try to make portions equal to serving sizes recommended by the government's Food Pyramid and ones used in product labeling. "We take these nutritional guidelines and translate them right onto the plate," says Carol Jubert, program designer for Portion Doctor made by Portion Health Products in St. Augustine, Fla.
For example, the Portion Doctor plate is divided into three sections -- the largest meant to hold a cup of vegetables, another to hold half a cup of potatoes, pasta or rice, and the third to hold 3 ounces of meat, poultry or fish.
Another product, the EZ Weight plate, distributed by L&L of Luling in Luling, La., is divided into eight compartments: two teaspoon-size, two tablespoon-size, two that hold a cup each, one that holds two-thirds cup and one that holds 6 ounces. It comes with an instruction manual that lists recommended amounts of various foods.
Although people could use scales or measuring cups, "people don't like to," says Laurie Acosta, one of the designers and the dietitian for the EZ Weight Plate. "They want something easier."
Last year, the Archives of Internal Medicine published the first, and so far the only, study of a portion-control plate -- the Diet Plate. Available in male and female versions (the latter intended to yield lower-calorie meals), the Diet Plate is divided into sections for carbohydrates, proteins, cheese and sauces, with the rest of the space for vegetables.
All study participants were obese, had Type 2 diabetes and were required to eat most of their meals at home. Of the original 130, 122 completed the six-month study. The group using the Diet Plate lost more weight overall than the group who didn't use the plate. A greater proportion of those using the plate lost at least 5% of their weight -- an amount that's been shown to have significant health benefits -- and more of them were able to lower the levels of medication they were taking to treat their diabetes.
However, the study also may have revealed some limits on what portion-control plates can do. "This is a population who are highly motivated to lose weight so they can reduce meds, and yet only 17% lost more than 5% [of their weight]," says Roberts of Tufts University. "I know that will have some health benefits, but in terms of the big picture, it isn't a whole lot."
More than serving size
The basic concept underlying portion-control plates -- if you eat less, you'll weigh less -- is beautiful in its simplicity. "And considering what people eat, anything smaller would be better," says Ruth Frechman, spokeswoman for the American Dietetic Assn. in Burbank.
But many experts caution that the concept is a little too simple and that it matters what you have a portion of.
"Calorie density," Rolls says, "has an even bigger effect."
Portion-control plates take density into consideration somewhat. They often come with information about healthful eating, even sample menus. And calorie-dense carbs and proteins are given much less space than low-carb veggies, for instance. But on one of these plates, a piece of steak is equivalent to a piece of white fish if both fit into the allotted room. Steak and white fish are far from equivalent calorically.
"If a person replaced 3 ounces of broiled strip steak [trimmed of fat] with 3 ounces of broiled white fish [prepared without fat] once a day over a year, the calorie savings is approximately 24,000," Gorman says. "A 24,000 calorie deficit over a year can turn into a 6-pound weight loss."
Another problem: Spaces on the plates may be limited, but how high folks pile food into these spaces is often left to their discretion -- which isn't always the better part of dieting.