Ironically, preliminary research suggests that some dietary protein — such as that from eggs — may have a bigger effect on mood than carbohydrates, Fernstrom says.
Sugar takes the edge off pain.
This old wives' tale does get some support from science, Pelchat says. Studies have shown sugar to relieve pain in infants, which is why nurses give newborns sugar water before performing a heel stick, and rabbis give baby boys sweet wine before their bris. A meta-analysis published this year in the Archives of Disease in Childhood found that just a few drops to half a teaspoon of sugar takes the sting out of immunizations for babies up to the age of 12 months.
However, a study published in September in the journal Lancet cast doubt on this widespread belief. British researchers concluded that sugar merely inhibits babies' ability to register pain in their facial expressions; the brain activity of newborns as their heels were pricked was actually the same whether they were given sweetened or sterile water.
Any pain-relieving effect of sugar is difficult to demonstrate in adults because they have more complex palates, Pelchat says.
Chocolate brings good feelings.
Whatever mood boost chocolate gives you is all in your head, and that's OK, says Pelchat, who has been researching the relationship between chocolate and mood for nearly 20 years.
Chocolate contains many components with the potential to enhance mood, but the chemical effect of each of them is small. "It does have low levels of stimulants, but you can get a lot more from other substances," she says. "The caffeine content is very low, so coffee is better for that kind of kick. The sugar might give a temporary lift, but it's subtle. And the phenylethylamine that people say is supposed to make you feel in love — well, many foods, including salami, are much higher in phenylethylamine."
In North America and parts of Europe, women tend to crave chocolate around their menstrual periods, but in other countries, women crave black licorice. To Pelchat, that suggests that "chocolate is more of a cultural phenomenon than a physical one."
The other reason it may lift mood is because it's really delicious. "Anything we find delicious is part of a system that triggers the reward cascade in our brains," she says. "But what causes that cascade for one person doesn't necessarily do it for another."
Turkey makes you sleepy
People have often heard that foods rich in tryptophan — an amino acid plentiful in turkey and milk — will make them sleepy because it has a calming effect on the brain. But each molecule of tryptophan has to compete with many other amino acids to get into the brain, says Elizabeth Somer, a registered dietitian and author of "Eat Your Way to Happiness." A Thanksgiving feast will make you groggy, but tryptophan isn't the reason.
"Eating any big meal, especially if you also drink alcohol, is likely to make you feel sleepy," Kanarek says.
Omega 3 fatty acids found in fish help depression.
At the NIH, Hibbeln has spent two decades studying the effects of omega-3 fatty acids on depression and other mood disorders. The evidence that eating fish high in omega-3s can help is strong, he says.