How you could be eating more and not know it

Shari Roan from the LA times reviews some of the key studies which aim to explain nonconscious influences promoting calorie intake:

"People can be influenced to eat unhealthful food, or more food than they should, without even realizing it.

* Advertising matters. One study, published last year in the Journal of Consumer Research, found that people think they are eating healthfully if it's advertised that way. Researchers had people eat Subway meals that contained the same amount of calories as a McDonald's meal, but the people estimated that the Subway meal contained 35% fewer calories.

* Eating is automatic. A 2004 study in the journal Appetite showed that people who are served bigger portions will eat more. Men given large bags of potato chips ate triple the number of chips -- an extra 311 calories -- compared with men given a small bag of chips.

* Visual cues prompt eating. A 2004 study in the Annual Review of Nutrition found that people ate 69% more jelly beans when they were offered in a mixed assortment than a group offered jelly beans sorted by color.

* The setting matters. A 2005 study in the journal Personality and Social Psychology Bulletin found that the more pleasant the environment, the more people will eat. People shown a picture of a smiling person poured more of a drink, drank more and rated the drink more favorably than people shown pictures of a frowning person.

* Portions direct eating. A 2003 study in the American Journal of Clinical Nutrition found that doubling the size of an entree increased overall food intake 25%. The consumers did not compensate for the bigger entree by decreasing the intake of other food on their plates.

* Other people influence eating. A 1992 study in Physiology & Behavior found that food consumption increased 28% when one other person was present and 71% when six or more companions were present.

* Eating is contagious. A study published last year in the New England Journal of Medicine showed that obesity can spread through social networks. A person's chances of becoming obese increased 57% if he or she had a friend who became obese in the same time period. If one sibling became obese, the chance that the other would become obese increased 40%.

* Marketing matters. Several studies published in the 1970s and 1980s show that doubling the shelf space of an item in a grocery store increases sales of the item as much as 40%."