“I just ate a big lunch, and I’m so sleepy!” Chances are, you’ve heard this from others or said it yourself. Most adults have experienced this post-lunch lull, which makes us feel fatigued and saps our productivity.
But why does lunch always take the blame? After all, you don’t often feel sleepy after a big breakfast or dinner.
Actually, the fluctuations you experience in sleepiness and alertness throughout the day are symptomatic of the intricate sleep/wake machinery hard at work in your brain. Here’s why your sleepiness fluctuates throughout the day, and how this can be used to your advantage.
Why Am I Tired in the Afternoon?
There are two main processes that determine how sleepy you feel. The first process is called the homeostatic sleep drive. The longer you are awake, the more chemicals build up in your brain and send a signal to make you feel sleepy. The chemicals are cleared while you sleep. The buildup while awake explains why someone who has been awake for 24 hours feels very sleepy, and someone who has been awake for 48 hours can barely keep their eyes open.
Even though the homeostatic drive makes sense, you might reflect on your average day and think “I’m not increasingly sleepy as the day goes on.” You tend to feel very sleepy after lunch, and not so sleepy after dinner, even though you’ve been awake longer by then. Why is that? It’s all thanks to the second process in your brain that helps keep you alert. It’s called the circadian rhythm.
The Role of Your Circadian Rhythm
The circadian rhythm is an internal clock that works to keep your brain feeling awake at specific times of the day and at other times makes you feel sleepy. Your circadian rhythm takes a dip around 1-3 p.m., which most of us attribute to lunch.
However, it’s not your lunch that's making you sleepy, it’s a decrease in alertness from your body clock. You then get a strong signal to keep you awake as the afternoon and evening proceed, and you are particularly alert just prior to bed. This is why it can be very difficult to go to sleep earlier than your typical bedtime and why the hour leading up to your bedtime is often dubbed the “zone of forbidden sleep.”
Thankfully, as bedtime hits, the circadian rhythm quickly decreases its alert signal and allows you to fall into a deep sleep. The chemicals from your homeostatic drive are broken down and disappear while you sleep. Then the process starts all over again the next morning.
When you combine homeostatic sleep drive and the circadian rhythm, you realize that the times you are the most alert and awake tend to be mid to late morning, as well as early evening. These are ideal times to spend working on activities that require attention and vigilance. It’s best to perform boring, mindless activities and chores around the afternoon lull from 1-3 p.m. — as long as you can keep yourself awake.
So the next time someone at the office tries to blame lunch for their sleepiness, tell them the truth: It’s not lunch’s fault after all.