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Key points
- It is important to know whether what we eat for lunch may inadvertently cause our afternoon mental performance to flag.
- It has been found that high-fat food intake was associated with increased daytime sleepiness and decreased alertness.
- A study also found that excessive daytime sleepiness was associated with saturated but not unsaturated fat.
Many of us have experienced a mental/energy slump after eating lunch. The almost irresistible need to lie down and take a nap doesn’t occur immediately. Our heads don’t fall onto the empty dessert plate, and we are usually alert enough to get ourselves back to the office or home.
But about 45-60 minutes after we finished eating that delicious lunch, we wish that our daytime job was testing the softness of mattresses.
Known as the postprandial (after a meal) slump or torpor, the lethargy that envelops us has been attributed to the volume of food consumed during the meal, and if alcohol has been consumed, that also.
Many cultures that used to designate lunch as the main meal of the day followed this meal by a mandatory rest; stores were closed from 1-4 pm, and workers and children went home for their midday meal and then rested or slept until late afternoon.
Woe unto the tourist who expected to be able to shop in the early afternoon and found every store concealed behind a metal shutter. Presumably, remote work should allow for such a work pattern to be reestablished, but that has not happened.
The commonly accepted reason for this diminution in energy is the increased blood flow to the gastrointestinal tract away from the brain, but it is still not understood why sleepiness should result. The urge to nap after the Thanksgiving meal has erroneously been attributed to consuming turkey, and supposedly linked to increased tryptophan uptake into the brain. Since protein prevents tryptophan from getting into the brain, the real reason may be the consumption of considerably larger than normal amounts of food, and/or foods high in fat, and/or alcohol.
Given the absence of workplace forgiveness for napping on the job after lunch, it is important to know whether what we eat for the midday meal may inadvertently cause our afternoon mental performance to flag. Moreover, perhaps we should know whether the surgeon who is operating on us at 2 pm, or the pilot on our afternoon flight, ate a meal that will blur his or her alertness and attentiveness.
Several years ago, a paper was presented at the 27th annual meeting of the Associated Professional Sleep Societies LLC that suggested daytime sleepiness was affected by nutrient intake at lunch. Non-obese men consuming diets high in fat, protein, or carbohydrate were tested for daytime sleepiness and sleep quality at night.
High-fat food intake was associated with increased daytime sleepiness and decreased alertness. The deterioration in alertness was sufficiently great to be a possible deterrent to the performance of specific jobs, according to the author of the study.
Similar results were described in a large Australian study among more than 1800 Australian men. The men, age 35-80, participated in a yearlong study during which their food intake, sleep patterns, and daytime alertness were monitored. There was a positive relationship between mealtime fat consumption and daytime sleepiness, suggesting, as found in the previous study, that alertness may be impaired by the consumption of this macronutrient.
Clearly, breakfasts of cheese omelets, sausage, fried potatoes, and buttered biscuits should not be consumed before taking the Bar exam or presenting a report at work. Lunches similarly loaded with fat such as a Double Whopper with cheese (69g of fat), or Subway's Double Meat Italian BMT foot-long sandwich (70 g fat) should also be avoided, if afternoon activities require alertness or attentiveness.
However, not all fat needs to be avoided. Another study from Australia on excessive daytime sleepiness found an association with saturated, but not unsaturated fat. Avocado toast, tuna salad tossed in olive oil and vinegar marinade (rather than mayonnaise), a chicken stir-fry heated in sesame oil, or salad tossed with a tahini dressing are foods that contain unsaturated fats.
These studies are useful in planning meals that may precede meetings, lectures, fund-raising speeches, and even auditions. If the audience and the presenters are to be at their best, they should not be served food that may influence their postprandial alertness.
Case in point:
Years ago, I was invited to a dinner followed by a talk by a well-known author. The event took place in a private club known for its elaborate cuisine. A pate was followed by a cream soup, followed by a cheese-heavy side dish to the filet mignon. The dessert was fudge cake topped with a dollop of whipped cream.
By the time the speaker had been introduced and stood up to speak, gentle snores were heard around the room, and more than one head was on the tablecloth. Such a menu, I concluded, should be used only if the speaker is known to be very boring.
It is not necessary to dine on boiled chicken, lettuce sprinkled with lemon juice, and steamed rice to avoid a “fat fog’” in your head after the meal. But choosing to consume leaner rather than fattier foods will maintain your mental sharpness and avoid the temptation to sleep through someone else’s presentation.
