1853: Once Per Day

Explain xkcd: It's 'cause you're dumb.
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Once Per Day
I'm not totally locked into my routine—twice a year, I take a break to change the batteries in my smoke detectors.
Title text: I'm not totally locked into my routine—twice a year, I take a break to change the batteries in my smoke detectors.


Many news reports on health recommend the "best" way to perform the processes, such as eating, drinking, exercising, or sleeping, that are required to live healthy. These reports tend to give such factors as a type of food to consume regularly, the amount of a nutrient to consume, or how long to exercise, in terms of what or how much to do daily. A simple example of this is the proverb, "An apple a day keeps the doctor away." Perhaps this kind of advice is overthinking things, but Cueball decides to follow it strictly as explained in the caption.

So when Megan asks Cueball what his plans are, he just lists his routine consisting only of things that the news has told him exactly how often to do.

His list includes the following, which he has to do once per day:

  • Eat an apple - This references the common old wives tale of "an apple a day keeps the doctor away"
  • Eat an egg - One egg would provide protein. This could also be a stand in for "breakfast is the most important meal of the day"
  • Take one aspirin - Aspirin can reduce heart issues. Baby aspirin would contain a lower dose and be safer.
  • Eat a piece of dark chocolate (see also John Bohannon's chocolate study for an example of how bad science can wind up as such "you should do ... daily" suggestions in the media) - Dark chocolate would contain more antioxidants and less sugar.
  • Drink six glasses of water - There is a common, long standing myth that you're supposed to drink X amount of water per day. Some say 6 or 8 cups. A liter or two. etc. etc.
  • Drink one glass of red wine - Always used as a "health can be fun" example. Wine is reputed to contain significant antioxidants, and one glass a day has been advanced as a "safe" amount to drink.
  • Drink a cup of coffee - Coffee is one of those health items that has a new health benefit or loss every week, depending on which media outlet you follow.
  • Drink a cup of tea - Tea's health benefits are a very common subject. There is much media talk about the benefits of different types of teas, usually focused around Green Tea.
  • Get 30 minutes of exercise - Different media outlets give different amounts of exercise to do. Usually, they tend towards 15-30 minutes a day to sound easy and low commitment.
  • Get 8 hours of sleep - An average adult needs 6-8 hours of sleep daily, but this varies per person, and by age.

Several obvious problems arise with these "you should do ... daily" tips. They are often based on population studies, but they may be harmful in the case of some individual persons. This health-related advice would be beneficial in, say, 60 or 70% of the population, but may be ineffective in other 20% of the people, and deleterious in 10%. This especially relates to the suggested daily intake of aspirin.

The second problem is the shaky scientific foundation of this advice. Some of this advice (such as eating and apple a day and drinking six glasses of water) is based on old sayings without any clear scientific backing. Other pieces (such as a daily aspirin, or a glass of red wine), were based on preliminary studies, and subsequent conflicting data has thrown them into serious doubt (the benefits may be smaller or non-existent, and may be outweighed by the negative effects). It is unfortunately common for news outlets to excitedly report on individual studies that show intriguing results, giving the public the impression of scientific consensus, while actually scientists are still cautioning that there's not enough evidence to make clear recommendations.

Moreover, Cueball implies that he only does these things every day. It's not clear whether following all of these pieces of advice take up all of his time, or whether he considers each day to be complete when he's finished his daily tasks (other than sleeping and exercising, the other things on the list shouldn't take up much time). In any case, doing nothing other than those specific routines would be harmful in a variety of other ways.

In the title text Cueball explains that his daily routine is not completely fixed. It is broken twice a year, since he also follows public information campaigns suggesting the replacement smoke detector batteries twice a year. While the US National Fire Protection Association recommends a replacement at least once per year others suggest every time when the clock changes according to daylight saving time, i.e. twice a year. (All such recommendations will likely become irrelevant as citizens of the United States, starting in California, are encouraged to replace their existing smoke detectors with new models containing irremovable ten-year batteries.) This is just another example for official overdone recommendations nobody follows, in this case since smoke detectors make annoying beeps when their batteries run low and thus rarely need routine replacements before then.


[Megan and Cueball are standing together, facing each other.]
Megan: Got any plans for the day?
Cueball: I'm going to eat an apple, an egg, one baby aspirin, and a piece of dark chocolate, drink six glasses of water, one glass of red wine, a cup of coffee, and a cup of tea, then do 30 minutes of exercise.
Cueball: Then back to sleep for another 8 hours!
[Caption below the panel:]
I only do things that news stories have specifically told me to do once per day.


  • Fire alarms were also the subject at 1794: Fire.
  • Drinking six glasses of water per day has been the subject in 1708: Dehydration, and earlier, when it was more common to say eight glasses per day, in 715: Numbers.
  • If Cueball actually did all these things once per day, then he would have to stretch out the eating and drinking over 15 hours and 30 minutes.

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At 60 calories for an apple, 157 calories for the red wine, 74 calories for the egg and assuming 6-7 ounces of dark chocolate, one could take 10 years to starve to death on this diet. But you ain't going to be exercising on only 1300-1400 calories per day.Seebert (talk) 16:22, 21 June 2017 (UTC)

Depends on the type of exercise. He could mean exercising his mind. But the total time it takes to accomplish all of that (including sleep) means that his "day" would last at most 11 hours. His circadian rhythm is going to be all sorts of messed up. OldCorps (talk) 17:56, 21 June 2017 (UTC)

I've tried improving the explanation but in my opinion, it's still quite rough. Feel free to edit phrasing. ~AgentMuffin

Randall get out of my head! This morning like EVERY working day I took the train to the World Trade Center walked up 130 steps from the platform to the street and another 15 minutes to work. Sat down to eat my daily breakfast of oatmeal plus a spoon of dark bakers cocoa, a hard boiled egg and a cup of coffee. For lunch I will eat a plain Greek yogurt, two pieces of whole grain bread and two fresh fruits (an apple and something else) and at the end of the day I will walk another 15 minutes and down the stairs to the train stop to go home and set the timer to get my healthy 8 hours of sleep. I'm a living Cueball (except I have hair). Ouch! This is no joke. Rtanenbaum (talk) 14:30, 22 June 2017 (UTC)

I take issue with the statement that "adults require 6-8 hours of sleep". (Yes, I'm nitpicking, but nitpicking is an ExplainXKCD staple, so nyah! LOL!) As someone who has suffered from sleep issues all his life, I've always paid attention when the subject has come up, and literally EVERY recommendation has been 8 hours for adults, with children requiring more. In recent years I've heard that suggestion adjusted to say less can be okay (but still at least 6), as long as it's once in a while, and the adult usually gets 8 hours. So 6 hours on weeknights isn't enough, 8 hours weeknights and 6 weekend nights would be fine. :) NiceGuy1 (talk) 04:40, 27 June 2017 (UTC)

I added in most of the explanations. There is a reason I said an "average" adult requires somewhere in the range of 6-8 hours, varied by person by age. I know adults who are fully functional on 6 and some(like me) that requires 8. And while anecdotal evidence isn't evidence at all, I phrased it more vaguely to be inclusive. This comic is in general makes fun of the fact that these recommendations are always so specific but would affect people in different ways. Zazathebot (talk) 21:57, 10 August 2017 (UTC)

The latest researches suggest that any amount of alcohol intake would have a negative impact on health. Drinking wine is no longer considered a healthy practise if you are a teetotaler. Dousha99 (talk) 13:39, 30 March 2021 (UTC)

Please check the Recent Changes page at least ****** times per day.[citation needed] ClassicalGames (talk) 12:05, 3 May 2023 (UTC)

I think that the egg has less to do with protein and breakfast and more to do with the good cholesterol in it. There's both good and bad cholesterol, with bad cholesterol clogging up blood vessels and good cholesterol knocking the bad cholesterol out of the way which clears up the blood vessels again. Please note, I'm not a nutritionist. Look up this information for yourself before quoting me. Kapten-N (talk) 11:46, 13 March 2024 (UTC)