When you think about Thanksgiving, science is probably not the first thing that comes into your mind. It seems much more aligned with history, and of course, the culinary arts. However, beneath the eating and thanking, there’s a lot to be learned!

Turkey

Turkey is a Thanksgiving cornerstone. It is a common belief that eating turkey makes you sleepy, because of the high levels of tryptophan it contains. Looking at the science, this sounds reasonable at first glance. Tryptophan is a component of the brain chemical serotonin, which is converted to melatonin, a hormone that signals sleep. However, digging a little deeper makes matters less straightforward.

In reality, the tryptophan levels in turkey are nothing impressive. Tryptophan is found in a large number of other foods, including eggs, cheese, and milk. Chicken has similar levels of tryptophan as turkey, and cheddar cheese has even more. There are scientific reasons why people grow drowsy after eating a Thanksgiving feast, but that has more to do with the other foods on their plate than turkey.

Carbohydrates are a dominant component of many favorite Thanksgiving dishes. Eating carbohydrates triggers the release of insulin into the bloodstream. Insulin causes many amino acids to be absorbed by muscles, but not tryptophan. This leads to a higher ratio of tryptophan in the bloodstream compared to other amino acids, which results in more tryptophan being taken into the brain. This creates a rise in melatonin and feelings of drowsiness. However, turkey alone is not enough to create this effect. It is really the carbohydrates that activate this cascading response.

Of course, even people who consume no tryptophan at all may find themselves sluggish after gorging themselves on Thanksgiving. After you eat a large meal, blood is diverted from the brain towards the stomach to aid with digestion. This can easily create lethargy, especially when combined with alcohol.

Pumpkin Pie

The science behind pumpkin pie is not a question of neurotransmitters or hormones. Rather, many pumpkin pies are suffering from a case of mistaken identity. As much as 85% of commercial pumpkin pie filling does not contain any of what we traditionally call pumpkin, Cucurbita pepo. Instead, it contains other squash of the species Cucurbita moschata, such as Golden Delicious, butternut, or Boston Marrow.

Even though it would be hard to mistake a butternut squash for a pumpkin, purees containing only C. moschata are still allowed to be sold under a “100% pumpkin” label. The USDA states that “the distinction between pumpkins and winter squash is culinary rather than taxonomical.” This means that pumpkins and squash are such close enough relatives that the USDA does not consider them separate entities, except in how they are used for cooking.

This beautiful rainbow of squashes are all cucurbits and could be considered pumpkins by the USDA definition. Photo by Harald Bischoff — This beautiful rainbow of squashes are all cucurbits and could be considered pumpkins by the USDA definition.
Photo by Harald Bischoff

Pumpkins and squash are both members of the genus Cucurbita. Genera (the plural of genus) are composed of closely related species. Even though this genus evolved fairly recently, its species are widely diverse. All varieties of squash are cucurbits, from pumpkins to ornamental gourds.

Cucurbits evolved in the Americas and were an important food source for natives throughout the Americas. They were domesticated over 8,000 years ago. Wild cucurbits are small, bitter, and mildly toxic. Domesticated squash are much larger and sweeter, more palatable for both humans and animals. Domesticated squash cannot live in the wild, leaving this bounty of squash diversity dependent on humans for survival.

If you want a truly authentic pumpkin pie, you may have to make your own pie filling from scratch. Just remember that many pumpkin varieties are not as tender and flavorful as their squash cousins!

Being Thankful

Food may take the center stage at Thanksgiving, but it is also a time to reflect on what we are grateful for. There is science to suggest that being thankful actually is beneficial for health. At the University of California, a team of researchers have devoted years to determining how gratitude affects us. They manipulated levels of gratitude in lab, both naturally and by giving participants the hormone oxytocin (which influences social behavior). They discovered that people with higher levels of gratitude also had higher optimism and lower levels of anxiety and depression. Grateful people were more socially connected and less sensitive to rejection.

The hormone oxytocin increases feelings of trust, bonding, maternal behavior, and gratitude. It is sometimes called the "love hormone."

Gratitude changes the body on a biologic level as well. Grateful people have lower blood pressure, both when at rest and under stress. People with more gratitude also have lower levels of bad cholesterol. Grateful people even have better kidney function!

The one downside is that gratitude has been shown to be less beneficial when it’s forced, such as when put on the spot at Thanksgiving. Under these conditions, gratitude researcher Robert Emmons says that “Practicing gratitude becomes a burden rather than a blessing, making life heavier rather than lighter.”

Citing specific sources of gratitude is more effective than sweeping generalizations, such as saying that you are grateful for good health. If you want to make the most out of your Thanksgiving gratitude, consider listing specific things you are grateful for and taking the time to reflect over personal gratitude. Though the foods we eat can be unhealthy, devotion to gratitude is good for both the body and the mind.

- Kate Dzikiewicz, Paul Griswold Howes Fellow