Here's the Real Reason Thanksgiving Dinner Makes You Sleepy. It Isn't Just Tryptophan.

In a few days, many of us will be splayed sleepily across Mom and Dad's living room couch, an empty plate that once held swaths of turkey and mashed potatoes not far from our fingertips. Nothing can induce a spontaneous bout of napping like a hefty Thanksgiving feast.

Lore has it that tryptophan, the amino acid found in turkey, is the primary culprit. Tryptophan causes your brain to produce serotonin and melatonin, which make you feel relaxed and sleepy. 

But if that's the whole explanation, why didn't I pass out after every turkey sandwich I ate in high school? And why do we not experience a similar profound sleepiness when we eat pumpkin seeds, tofu and cheese — other foods that contain as much, if not more, tryptophan than turkey? 

Clearly, the tryptophan in turkey can't entirely be to blame. 

The real reason Thanksgiving dinner makes you sleepy: It's not just the turkey. It's the fact that you're also gorging on carbohydrate-heavy foods such as mashed potatoes, stuffing and pie. 

Those foods cause a spike in blood sugar, which your body fights by producing lots of insulin. When insulin and other amino acids team up to regulate your glucose levels, they leave a clear path for the tryptophan to access your brain. 

That leads to increased production of other hormones, such as serotonin and melatonin — "chemicals that will make you drowsy so that you slow down and just digest," Mary Hartley, a nutritionist from Providence, Rhode Island, who blogs at Ask Mary RD, told Mic. 

To simply blame the turkey is to overlook "a constellation of hormones and neurotransmitters — not just tryptophan — [that] have an effect," Hartley said.

And that's to say nothing of the myriad external factors that might make you drowsy around the holidays.

"These biological processes coupled with stress, a busy schedule leading up to the holidays and lots of traveling make it easy to understand why many of us feel tired on Thanksgiving," Alexandra Miller, corporate dietitian at Medifast, told Mic.

So how can you avoid conking out post-feast? Miller suggests making 80% of your meal "lean and green," as she puts it. That means lean proteins such as "white turkey meat, seafood, pork chops or boneless skinless chicken breast that have been baked, roasted, braised or grilled," she said. As for the "green," she said, "fill half of your plate with non-starchy vegetables, such as broccoli, green beans or mixed salad greens."

"The 'lean' part of the meal provides protein, while the 'green' part provides fiber, both of which will help fill you up and keep you satisfied throughout the day," Miller explained. "Lean protein and vegetables are also a rich source of vitamins and minerals, which are needed to keep your immune system strong, spirits high and metabolism working properly."

Miller also gave tips to avoid "mindlessly munching all day." 

"Occupy your hands with a hot cup of unsweetened tea or cold glass of infused water," she said, suggesting people try "new flavors of tea, such as baked cinnamon apple, chai or apricot vanilla crème, as well as different combinations of fruits, vegetables and/or herbs to make infused water, such as cinnamon sticks with slices of apples or oranges or cucumber slices with fresh blackberries."

Chewing on peppermint gum or brushing your teeth after a meal will also remind you to stop stuffing your face.

What if you're stricken by a barrage of sleep-inducing chemicals? Don't resist it. "All it does is cause you to be sleepy so that you rest and digest," Hartley said. It's your body's way of telling you it needs to chill out and process all the food you just consumed.

If you're feeling sleepy, Hartley advises against heading out on that post-meal family jog. "Don't try to divert blood supply from middle of body to periphery when you're trying to digest," she said. 

People need to be OK with giving in to the nap attack. "If they're going to eat a big meal," Hartley said, "it only makes sense to listen to their body."

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