Why You Really Run Out of Gas Every Afternoon

... and what to do to power past the fatigue.

Posted Oct 08, 2014

Indeed, the fatigue sometimes seems so overwhelming, especially when the work preceding late afternoon has been mentally and emotionally stressful, that our bodies feel as if we've been on a construction site all day. (Maybe we have.) A friend who is a litigator told me that doing a cross examination in a courtroom leave him more exhausted than two days of yard and house chores, even though his courtroom physical activity is limited to standing, sitting, and occasionally walking a few feet away from his chair.

“There is something peculiar about late afternoon,” he told me. “I consider myself a pretty calm guy and able to resist reacting to insults or challenges from other lawyers or a judge. But around 4 pm, I feel myself either feeling suddenly sensitive to the tension in the courtroom, or overcome with profound fatigue.”

A late afternoon slump can descend on anyone—a UPS delivery person, a daycare assistant, or a neurosurgeon—and it is more likely to occur as the days shorten and the light outside no longer feels like midday, but like the start of evening.

Magazines and websites are full of advice about this problem—most of it entirely wrong.

Many assume that this slump is caused by the body’s need for energy, and recommend eating a bigger lunch or snacking to increase low blood sugar. But the cause of this fatigue and mood change resides in the brain, not in the blood.

Is anyone really famished at four in the afternoon? Sure, if someone exercises at lunch but doesn’t eat afterward, he or she will be quite hungry by late afternoon. But the rest of us? Beyond infancy, we do not need to be fed every three, and so even if lunch is over at 1 pm, our bodies really do not have to be fed again three hours later.

But our brains are different.

To understand what lies behind the urge to nap rather than write a report in the late afternoon, we have to see what is going on with serotonin, the brain chemical which attempts to keep us energetic, focused, and in good humor.

Something happens late in the afternoon to the activity of serotonin. There may not be enough of this neurotransmitter, or its activity may slow down; whatever the mechanism, the result is a deadening of mood, motivation, and mobility.

We discovered this en route to studying something else: why many people wanted to eat a sweet or starchy carbohydrate snack late in the afternoon. Volunteers were living in a research residence where snacks where available 24/7. But they never snacked until late afternoon. Why then? They told us they felt their mood deteriorating at that time. They felt depressed, tense, impatient, and tired. They could not concentrate. But they claimed that after they ate some carbohydrates, they felt better.

This was all anecdotal, interesting, but not scientifically valid. We wanted to know: Did they really feel better after eating carbohydrates or just thought they did because they liked to snack?

The truth is, they really did feel better. We know because at one time, we gave them a drink that contained enough carbohydrate to increase the production of serotonin in the brain (serotonin is made only after carbohydrates are eaten, not protein) and at another time, we gave them a drink that did not increase serotonin; it contained protein.

Their moods and fatigue were tested before the drinks and then again an hour or so later. The carbohydrate drink did improve their moods, and they were less tired after having it. But they did not experience the same results after the protein drink.

The volunteers taught us something very useful: If you want to lift yourself out of a slump eat a carbohydrate snack. (This does not apply to baseball.)

With that in mind, here are two suggestions to lift late afternoon mental and emotional fog:

  1. Eat 25 grams of a starchy carbohydrate such as pretzels, popcorn, graham crackers, or a piece of bread. Avoid any starchy food with fat, which will make you feel lethargic and dull. And don’t eat fruit (at least, not for this specific purpose): No serotonin is made after consuming fructose.
  2. Move, vigorously. Swallow your snack, then get up from your chair and do something physical. Find a staircase and climb it a few times. Take 10 minutes to jog around the block. If you're home, find a jump rope, set the egg timer, and jump for 3 minutes. Or if you have a treadmill or bike, run or pedal for 5 minutes until your heart rate goes up.

Your brain will thank you. Now go back to work.