People often say they are addicted to chocolate, but few studies have ever shown any evidence for true addiction to this widely craved sweet.

Rather, chocolate is irresistible partly because we know we're not supposed to have too much, says Peter Rogers of the University of Bristol in England.

Presenting his idea Tuesday at the annual BA Festival of Science held at the University of York, also in England, Rogers noted that people readily label themselves chocoholics, with the assumption that chocolate has mood-enhancing ingredients.

• Click here to visit FOXNews.com's Human Body Center.

There is little evidence to support that idea, Rogers said. The stuff in chocolate said to be pharmacologically significant — serotonin, tryptophan, phenylethylamine, tyramine and cannabinoids — exist in higher concentrations in other foods with less appeal than chocolate.

"A more compelling explanation lies in our ambivalent attitudes towards chocolate," Rogers said. "It is highly desired but should be eaten with restraint (nice but naughty). Our unfulfilled desire to eat chocolate, resulting from restraint, is thus experienced as craving, which in turn is attributed to 'addiction.'"

Milk chocolate and chocolate-covered candies, the most popular forms of chocolate, contain less cocoa solids, and therefore a lower concentration of potentially psychoactive compounds, than dark chocolate.

So, Rogers argues, chocolate's appeal and its effects on mood are likely due mainly to its main ingredients, sugar and fat.