Chocolate has been singled out as the food of love pretty much ever since people started consuming it.
According to Sophie and Michael Coe's eminently reliable book The True History of Chocolate, a Spanish conquistador reported that the Aztec emperor was given during the course of a great banquet "a certain drink made of cacao, which they said was for success with women."
Later, when chocolate had been brought back to Europe, members of the Catholic Church debated ferociously over whether chocolate was an aphrodisiac, or simply a beverage that refreshed body and spirit. Amusingly, a story was told about St. Rose of Lima being presented with a cup of chocolate by an angel -- surely divine proof that chocolate was no sinful food, but as pure as the messengers of God themselves.
The civilian population was eager to embrace the idea of chocolate as a food that promoted ardor, especially in women. Paul Richardson's wonderful book Indulgence quotes a hilarious poem by James Wadsworth, in which the author insists that consuming chocolate will make even old women feel suddenly youthful and ardent again, "And cause them long for you-know-what, if they but taste of Chocolate."
There's no scientific evidence to support any such claims. True, one study conducted by researchers at the University of Milan (Italy) seems on the face of it to support the idea that women who eat chocolate on a daily basis feel more desire, and enjoy greater pleasure in the act of love. However, those women in the study were also younger than the women who didn't eat chocolate regularly. Once age was factored in, there wasn't much difference between the two groups.
The question remains: why do we think of chocolate as a magically romantic substance? True, it's a natural source of chemical stimulants -- both caffeine and its cousin theobromine (which may be responsible for the euphoria many report experiencing after consuming the treat). But coffee is loaded with much higher amounts of caffeine, and smells just as good in its own way as chocolate does; yet though meeting someone for coffee is a common date, coffee is also a mainstay of business meetings, which aren't exactly known for their exciting, amorous atmosphere.
Maybe it's chocolate's sweetness? Fruits, which are naturally sweet, are often associated with love and loving. But chocolate in its early days was a beverage that wasn't necessarily sweetened, but was quite harsh, and it had just as strong a reputation then as now as being an ingredient for passion.
At any rate, chocolate is now certainly considered the food of love. When given as a gift from a man to a woman, it signifies a serious romantic interest. And it certainly seems to summon a response. Watch a woman's face light up when she receives a beautiful box of chocolates. And that's before she's even had the chance to eat one.
Maybe that's the real source of chocolate's supposed aphrodisiac powers: gratitude. As Jane Austen points out in her most romantic novel, Pride and Prejudice, gratitude can be the strongest inducement to love there is -- and what could make a woman more grateful than a gift of her favorite sweet?