With Thanksgiving rapidly approaching, many families are planning their holiday meal, including stuffing, sweet potatoes, cranberry sauce, pumpkin pie, and, above all, the turkey. Why is turkey so important on Thanksgiving? It is assumed that this tradition originated in an event commonly referred to as the “first Thanksgiving”. There is evidence of a meal shared by the Pilgrim settlers at the Plymouth colony in Massachusetts and the Wampanoag people in late 1621, as described in a letter written by Plymouth colonist Edward Winslow. Winslow’s letter said that the Pilgrims provided wild fowl, while the Wampanoag brought deer to the shared autumn harvest feast. By the turn of the 19th century, turkey had become a popular dish to serve on holidays because it was plentiful, readily available, and big enough to feed a family. In her 1827 novel Northwood: A Tale of New England, writer Sarah Josepha Hale devoted an entire chapter to a New England Thanksgiving, with a roasted turkey “placed at the head of the table” and campaigned to establish Thanksgiving as a national holiday in the United States. In 1863, Thanksgiving was finally declared an official holiday with a presidential proclamation by Abraham Lincoln.
Turkey is noteworthy not only as a symbol of Thanksgiving, but also from a nutritional perspective. It is rich in B vitamins and it is a good source of choline, phosphorous, selenium, magnesium, potassium, zinc, and iron. Zinc, iron, and vitamin B12 can be difficult to obtain in diets free of red meat, so turkey may be an appealing alternative for those who avoid red meat. In addition, turkey is a great source of all amino acids, and especially tryptophan. A three-ounce serving of turkey can provide as much as 264 mg of tryptophan, or about 75% of the recommended dietary allowance.
Tryptophan is an essential amino acid needed by the body to function properly, but the human body cannot synthesize it on its own. It needs to be obtained from dietary sources, including poultry, beef, pork, fish, soy, dairy, eggs, and some nuts, seeds, and grains. It has an important role for several key physiological functions, including nitrogen balance, muscle growth and maintenance, the production of proteins, enzymes, and neurotransmitters, and for healthy growth in infants. Tryptophan also has a supportive role in the endocrine system, as a precursor to serotonin and melatonin, hormones that help regulate the circadian rhythm, appetite, mood, and sleep. A controlled double-blind crossover study (n = 35) found that the consumption of a tryptophan-rich egg protein hydrolysate resulted in an increase in plasma tryptophan uptake into the brain and improved mood and performance under acute stress exposure. Furthermore, tryptophan is utilized by the liver for the biosynthesis of niacin (vitamin B3) and nicotinamide adenine dinucleotide (NAD+), which promote energy metabolism, DNA synthesis and repair, and healthy immune responses.
The supportive role of tryptophan in healthy physiological functions has been widely investigated in a variety of clinical settings. For example, low serum tryptophan in individuals with coronary artery disease has been associated with immune activation and reduced life expectancy. Tryptophan insufficiency may also limit protein synthesis, including hemoglobin production, adversely affecting oxygen supply and increasing the risk of cardiovascular events and anemia. An epidemiological study (n = 231) found that increasing tryptophan consumption for one year was associated with lower cardiovascular disease risk.
A tryptophan-enriched diet has been reported to mitigate age-related decline in hippocampal serotonin (5-HT) production and the associated cognitive decline. This important amino acid has also been shown to modulate serum glucose and insulin levels and mitigate glucose absorption by the intestines, suggesting that tryptophan may support healthy insulin responses. Furthermore, a randomized crossover study (n = 25) reported that a high-tryptophan diet implemented for four days resulted in greater positive effect than a low-tryptophan diet, suggesting that tryptophan consumption may mitigate depression and anxiety symptoms. Finally, a cross-sectional study based on data from the National Health and Nutrition Examination Survey (NHANES) 2001-2002 (n = 29,687) found that tryptophan intake may be inversely associated with self-reported depression and positively associated with sleep duration.
There is ample evidence supporting the importance of tryptophan for optimal health. So when we sit down to enjoy the Thanksgiving feast this holiday season, whether it would be with a traditional roasted turkey or another tryptophan-rich treat, we could consider including this essential amino acid, and all of the important physiological functions it supports, in our gratitude list.
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By Antonia Toupet, PhD
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