It seems so simple: Serve people bigger portions, or use bigger plates, and they'll consume more.

Evidence that size matters – with food and non-alcoholic beverages, anyway – has been accumulating for years. Now the authoritative Cochrane Library has produced what it calls "the most conclusive evidence to date" by combining data from more than 60 independent studies into a meta-analysis.

Putting smaller amounts of food on a plate, or in smaller packages, or using smaller plates and cups consistently led both children and adults  to put less in their mouths. "If an effect of this size were sustained across the whole diet," the Cambridge University researchers wrote, it would reduce caloric intake by 16 percent in the UK—and a whopping 29 percent in the United States.

Change on that scale isn't likely, but the findings suggest a way that parents, chefs, and just about everyone else can cut significant calories from their diet without even feeling that they're dieting:

  • Try buying smaller plates. (It may not be easy – other studies have found that they grew 25 percent in the last century.)

  • Give kids more say around the dinner table. Research has found that children tend to serve themselves less than their parents would give them. (Just eating at home can help, as restaurant portions have ballooned in recent years.)

  • One study suggests the shape of tableware influences behavior—young adults drank less water from shorter, wider glasses than from taller, narrower ones.

A lot of the work on portion size can be traced to Penn State nutrition professor Barbara Rolls, a pioneer in the relatively small academic discipline who has mentored researchers around the country. Among them is Jennifer Orlet Fisher, an associate professor of public health at Temple University whose Family Eating Laboratory has conducted multiple studies in the even tinier field focused on children.

The Cochrane review included research from both of them.

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