Why Am I Sleepy After Eating Lunch? The Role of Circadian Rhythms

Afternoon Sleepiness Increases as the Circadian Alerting Signal Dips

A sleepy man at work in after lunch may benefit from a short nap, caffeine from a coffee, or simply waiting a few hours
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As you return to your work after eating lunch, you may wonder: Why am I so sleepy in the afternoons? Whether you use words like drowsiness, sleepiness, tiredness, or fatigue to describe this mid-afternoon lull, why does it occur? Is it because of what you ate for lunch? Well, it may actually relate to a natural dip in the alerting signal of the circadian rhythm. Discover how you can get through your afternoon without a cup of coffee or a nap.

Does Sleepiness Occur Due to Food Intake at Lunch?

It is normal to feel a little sleepy after eating lunch. Some people may mistakenly think that it relates to the consumption of food. In particular, some believe that there is a significant shift in blood flow from the brain to the stomach or gastrointestinal tract to aid in digestion. Although this sounds plausible, it doesn’t really make that much sense.

If this were the case, why wouldn’t we feel just as sleepy after eating a large breakfast or after dinner? One would expect the same change in blood flow would occur. The truth is that this sleepiness is unrelated to meals and is due to another cause.

Can Melatonin in Food Lead to Drowsiness?

Others may argue that there are elements within food that cause sleepiness. For example, there are minuscule levels of the hormone called melatonin. Although melatonin has an important role in the timing of sleep, the low levels within food are unlikely to have any significant effect.

There are some other foods that might make you feel a little sleepy, most notably turkey and foods that contain tryptophan. Tryptophan is converted by the body to serotonin, and then to melatonin, and (as noted above) this can enhance sleepiness. The effects are likely modest.

In addition, drinking alcohol may cause drowsiness. It does this because it enhances the effects of adenosine. In most cases, this is not what contributes to feeling sleepy after lunch, however.

The Role of the Circadian Rhythm in Afternoon Sleepiness

In fact, it has little to do with the food eaten (or that eating has occurred at all). Instead, it has more to do with the natural timing of an increased propensity towards sleep. There are two phenomena that contribute to this: the homeostatic sleep drive and the circadian rhythm.

The sleep drive is due to the gradual build-up of a chemical within the brain called adenosine. This reaches its peak right before bedtime, but it is also higher in the afternoon compared to the morning.

The longer a person stays awake, the more adenosine accumulates, leading to an increased desire for sleep.

The second process that contributes indirectly to sleepiness is the circadian rhythm. The circadian rhythm is actually the pattern of an alerting signal. It increases throughout the day to keep us awake and counteract the increasing levels of adenosine. There is a shoulder, or dip, in this pattern in the early afternoon, typically 7 to 9 hours after waking up. When the alerting signal dips, the underlying sleepiness shows itself, and we feel sleepy.

Most people naturally feel sleepy between 1 and 3 p.m. Interestingly, night owls (who may naturally fall asleep and wake later) often experience a delay in the timing of this afternoon lull as well. They may not feel sleepy until several hours later.

A Word From Verywell

Although feeling drowsy after lunch can be explained, there may be times when we are too sleepy. If we experience sleep deprivation, this after lunch sleepiness can be more pronounced. In addition, sleep disorders such as obstructive sleep apnea may make this worse.

To counteract the sleepiness that occurs in the early afternoon, you can try using caffeine or even take a short 10 to 20 minute nap. Each of these can reduce the adenosine levels that contribute to sleepiness. There can be other ways to stay up, too. Fortunately, if you tough it out, this period will pass and you will find that you feel more alert again in a matter of hours as the circadian rhythm revs back up. This normally occurs, even without a cup of coffee or a nap.

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Article Sources

  • Kryger, MH et al. Principles and Practice of Sleep Medicine. Elsevier, 6th edition, 2017.