A couple of nights ago, I went for a ride. My destination was only about 4 miles away from my house, and it was a downhill journey. Of course, I had to ride back up many hills to get back home, and didn't stay at my destination very long. The total journey was 8 miles. My bicycle is also a single-speed bicycle, so I didn't don't have the luxury of gears which resulted in a challenging ride.

Anyway, I woke up with a headache and nausea the next morning; this was about a week ago. According to the posts I've have read regarding headaches after cycling, I've come to the conclusion that I must be severely dehydrated because I'm still feeling the symptoms today, just not as much.

I'm just not very disciplined when it comes to sufficiently fuelling my body. I really want to take steps to prevent this kind of issue from happening again. I used to drink 4 litres of a water per day, but the regular trips toilet gave me the impression I was overdoing things when trying to consume 4L in a couple of hours, and so, I got into the habit of drinking when I felt like it which resulted in me drinking much less than 2L per day.

I'd really appreciate some input. Drinking water should be a straight-forward process, but regularly taking small sips like many people have suggested has never worked for me; I end up not drinking as much as I should for my weight of 175lbs/12.5 stone.

I should add that I'm probably in a calorie deficit due to eating 2 small meals per day rather than my usual 3-4 medium to large meals per day. I experienced this issue in the past (many years ago) after weight training (squats and dead lifts) on an empty stomach. A bottle of Lucozade and lying down for a couple of minutes fixed the issue. However, I'm sure many other factors were at play e.g. breathing technique and so one because I trained on an empty stomach years after that and it never happened again.

If the issue has nothing to do with dehydration, then it could be something to do with me not eating enough.

Main question:

  1. What is a common way to hydrate throughout the day at home, but also prior to/after a ride?

I have some additional questions:

  1. After becoming dehydrated, would it be best to rehydrate with water, or use some special kind of energy drink?

  2. Does repeated trips to the toilet when I consume water throughout the day mean I'm hydrating myself incorrectly? I definitely don't have a weak bladder.

  3. Should I be including the water I use in food, i.e. oats, as part of my daily water intake measure, or should I only be measuring water I drink directly?


  • This was in London
  • I consume very little salt. For example, breakfast consists of oats (made with water), crushed almonds, and fruit. The second meal I've been having is eggs, yams or potatoes and various vegetables. Very bland indeed, and definitely lacking salt from what I can see.
  • I've been riding regularly since December 2019, and prior to this, although I drive, I used to ride a lot. This is my first single-speed/fixed gear bike though. All of my previous bikes had gears, and riding up hills was easy, however, it's a totally different experience with a single-speed bike. It's much more work, especially with my gear ratio.
  • At the start of 2020 I was about 187lbs/13.5 stone, but the change of diet and reduced weight training caused me to lose a lot of weight. I wouldn't say my diet is a ketogenic diet though, but I'm starting to believe undereating was the cause of it. I had 4 meals yesterday, a lot of water, fruit and a glass of juice and the nausea and headache have gone. Looks like I really need to pay close attention to my diet.
  • I've been lifting weights a long time and I'd say I'm quite fit. Even when I take time off training, it doesn't take me long to get back in shape, and although the ride up the hills was challenging because I didn't really pace myself, I wasn't knocked out. I recovered quite fast, but the headache and nausea the next day concerned me.
  • 13
    Not sure if this was dehydration. Was this in London as your username suggests? A few miles in winter in England hardly leads to dehydration, the headache might just be from the cold wind.
    – uUnwY
    Commented Jan 3, 2021 at 1:38
  • 7
    4 miles, even with a lot of climbing, is not much. Unless you were hauling a trailer with a few people riding on it, there is no way you dehydrated yourself, and believe your hypothesis is incorrect. Far more likely you are sick or something else is at play. If you are drinking when you are thirsty, you'll be fine. Commented Jan 3, 2021 at 2:19
  • 3
    Alcohol consumption leading up to the 'health event' (Given the time of year, has to be asked) Have you had a Covid19 test?
    – mattnz
    Commented Jan 3, 2021 at 2:34
  • 3
    @Criggie: i think to bonk within 8 miles you'd have to be in such awful physical state that the answer would be self-evident. Commented Jan 3, 2021 at 4:18
  • 3
    If you are actively losing weight, i.e. intentionally eating little, then it's quite possible to run out of Glycogen in 8 miles, I think. That would mean you are on an almost ketogenic diet, but weren't quite over the threshold. Some people do that on purpose, the severe side effects wear off after a couple of days. That being said, I don't think this question is answerable on this site and I voted to close. If the issue persists, i.e. something similar happens again, consult a doctor or maybe dietician.
    – Nobody
    Commented Jan 3, 2021 at 15:19

8 Answers 8


Very unlikely you were dehydrated from such a short ride. If you were dehydrated post ride, you almost certainly started out dehydrated. Humans evolved to the top of the food chain by drinking when thirsty, the advent of the '8 glasses a day, drink all the time' has been popularized in my lifetime (First references appear to be a 1945 FDA recommendation), is controversial and largely debunked.

Worth a read.. but this is just one of thousands saying the same thing. (https://www.med.umich.edu/1libr/Gyn/ObgynClinic/8GlassesWaterMyth.pdf)

Do I need to drink 8 glasses of water a day?

No, you don’t.

Where does the 8-glasses guideline come from?

In 1945, the U.S. Food and Nutrition Board recommended that people drink 2.5 liters (84.5 ounces) a day. Evidently, most who read this then ignored the following sentence, “Most of this quantity is contained in prepared foods.” Whatever “prepared” meant in 1945, all food contains water, especially vegetables and fruits.

So that means you shouldn't drink 8 glasses of water per a day, but should get 8 glasses of water per a day from food and as water.

What I believe has happened is some people have lost the ability to listen to their body and know when its time to drink, and are so used to drinking a measure amount to a clock they now mistake the sensation of thirst for dehydration.

So how much to drink.... Drink when you are thirsty. Use the color of your urine to tell you if you are drinking too much or too little. Personally, if I am about to head out on a long event then I preloading a day or two before - Buts that is mostly because I tend to not drink enough, so the conscious effort is need to ensure I do not start out thirsty.

With all that out the way, say you really were dehydrated, not just hungover (which is mostly dehydrated with toxic by products of metabolized alcohol), had Covid 19 or one of many other medical conditions that cause headaches, what to do...

Rehydrate with water if its mild. If you want to rehydrate quicker, or it is moderate, rehydrate with an isotonic drink. Do NOT consume energy drinks, they use more water than they provide. Drink until you pee, then drink another litre is a reasonable point. You are recovered when your pee returns to normal color.

If the dehydration is severe, then you need medical intervention, likely a saline drip (Speaking from experience, magic, but like any medical procedure, negative side effects are always a possibility so should be avoided whenever possible)

  • 1
    Hi, I'm going to take a look at the document you linked. I actually feel so much better today. The nausea and headache have completely gone. The only change I made yesterday was eat 4 meals, drink a lot of water, eat some fruit, and have a glass of orange juice. I also took some Zinc; not sure if that has anything to do with me feeling better. I've set a reminder that fires hourly to remind me to have a drink if I'm thirsty.
    – LondonGuy
    Commented Jan 3, 2021 at 15:39
  • To be clear, dehydration can be a very serious issue on longer summer rides, and people can easily end up there (or in the effective toxicity of consuming only pure water hour after hour) without understanding that it is what is happening. But indeed, for a short duration ride in winter that seems unlikely to be the issue. Commented Jan 4, 2021 at 19:50

Your symptoms don't sound like anything to do with dehydration. The first and most reliable sign of dehydration is intense thirst. It's a myth that "thirst is too late" or that you need to drink before you're thirsty.

I'm just not very disciplined when it comes to sufficiently fuelling my body.

This usage of "fuelling" is advertising terminology invented by the people who want to sell you Gatorade and Gu. The calories you used for this ride were in the form of glycogen stored in your liver and your leg muscles, probably earlier in the day or even the day before.

If you're hungry, eat. But the food you eat generally takes many hours to be converted into glycogen.

  • 3
    It's important to recognize that beyond the situation of this question, extended hot weather exercise does in fact require electrolytes and sugar, not just water. If you consume only water and sweat it out, you strip your body of essential electrolytes, resulting in confusion, vomiting, and death. Sugar intake is ultimately key to absorption as well (and of course to staving off an eventual "bonk"). That doesn't mean you have to buy these products, but there's a point where what they are commercializing - sodium, potassium, and sugar - are in fact fundamental necessities. Commented Jan 4, 2021 at 20:11

I'll focus on this part of the question:

After becoming dehydrated, would it be best to rehydrate with water, or use some special kind of energy drink?

Normally, I don't recommend energy drinks simply to rehydrate.

Most drinks with electrolytes do contain carbs, but in theory that's a separate issue (e.g. Nuun tablets contain electrolytes but minimal carbs). Some simple carbs may (NB: not a nutritionist) help you absorb electrolytes. If you deplete your electrolytes, your power can drop off. Generally, a craving for salty foods will let you know that you've had your electrolytes depleted.

Also, cycling can burn a lot of carbs. If you cycle slowly for a long distance, you are burning a mix of carbs and fat, but you do burn a lot of total calories. If you are cycling intensely for long distance, you burn a ridiculous amount of total calories, the majority of which are carbs. Replenishing those enables you to ride further and, if you desire, faster. However, outside of cycling, I think it's a good general principle that we should limit the amount of processed foods, especially processed sugar. Thus, outside of a ride, I personally stick to drinking plain water to rehydrate. If I need supplemental electrolytes, I get that from my food - keeping in mind that things like frozen dinners and lunch meats have ample sodium already.

I used to stick to plain water even in hot weather. I persistently had mild headaches through the day, until I increased my electrolyte intake during rides and, in my case, my salt intake throughout the day (NB: I believe my sweat is fairly salty, but even if I'm wrong, I ride quite far and fairly intensely). Given the climate in England at this time of the year, though, this might not be the case for you.

I should add that I'm probably in a calorie deficit due to eating 2 small meals per day rather than my usual 3-4 medium to large meals per day. I've experienced this issue in the past after weight training on an empty stomach. A bottle of Lucozade and lying down for a couple of minutes fixed the issue. If the issue has nothing to do with dehydration, then it could be something to do with me not eating enough.

It sounds like you are on a diet. In addition to not being a nutritionist, I'm not even personally familiar with dieting. Normally, a 4 mile ride isn't that strenuous, but you are a new rider, and you experienced this while weight training as well. In a very general sense, it does sound like you may not be eating enough. Again, you do burn carbohydrates while exercising. You may not burn as much calories while weight training, but you do burn some, plus you do want to ensure your muscles get enough protein to repair themselves from that activity. You might want to re-examine your diet while exercising. I am not familiar with how much of a calorie deficit is safe while exercising. I do know that if you want to cycle a lot, you can't run a large calorie deficit.

  • Without knowing OPs general condition, weight, age we don’t know if he’s calorie deficit or not. For someone that’s 70kg two small meals maybe adequate depending on OP variations on small but two meals could be the equivalent of 1500 calories
    – Dan K
    Commented Jan 3, 2021 at 15:24
  • Just seen in OPs question he’s around 80kg so around the same as me
    – Dan K
    Commented Jan 3, 2021 at 15:25
  • I was cycling quite intensely, especially up the hills, but I recovered quite quick whenever the hill's angle levelled out. This gave me time to catch a quick a breath before encountering another hill. I feel my diet is the cause of this issue because yesterday (a couple of hours ago, because I think I posted the question after midnight) I ate a total of 4 meals, drank a lot of water, ate some fruit, and had a glass of orange juice. I also took some Zinc. I woke up feeling better today.
    – LondonGuy
    Commented Jan 3, 2021 at 15:50
  • @DanK I think I've been eating about 1100 calories. My diet and routine really changed this year. I lost a lot muscle and weight training at home just isn't the same. As I ate less food, my appetite changed. Weiwen Ng mentioned craving salty foods could let a person know they've depleted their electrolytes and the day before yesterday I was craving salty foods, but it was too late to eat, so I waited until yesterday. And today, I've woken up feeling better.
    – LondonGuy
    Commented Jan 3, 2021 at 15:58
  • 1
    @LondonGuy 1100 calories would roughly put you in a deficit of 7700 a week, were you aiming to loose around 1kg a week ? That’s an extreme diet. I aim for around 1600 a day and manage ok doing short rides around 10 miles daily. You need to work out why your dieting so much, if your training hard try and maintain your daily allowance probably around 2000 calories, more if your burning more to loose weight. I’m no doctor or nutritionist but 1100 is on the extreme end particularly if training daily also
    – Dan K
    Commented Jan 3, 2021 at 16:12

I often stop at gas station convenience stores when riding to just purchase a drink, finish it, and keep going on. Most places stateside those are open during corona shutdowns. In other years, the time-tested coffee shop or breweries.

  • 1
    I'm going to make sure I bring a water bottle with me next time. I most likely won't do strenous hill riding on an empty stomach after being in a calaroie deficit the previous day.
    – LondonGuy
    Commented Jan 3, 2021 at 15:42
  • 2
    Here in Austria cemeteries or soccer fields often have drinking water which is great to refill your water bottle. Keeps the stop short and you don’t have to pay for water. With 2*1ℓ bottles I generally only have to refill in summer.
    – Michael
    Commented Jan 3, 2021 at 15:49

Now you're pre-warned with some of the symptoms and results, consider doing the same ride again and see how you go.

Perhaps pace yourself a little better on the uphills, carry a full water bottle and sip from it periodically. Stick a banana, a sweet thing, or a gel in your pocket for just-in-case.

Personally I feel ratty riding if I'm low on sleep/tired too. Make sure you're getting enough quality rest.

And do take a rest day occasionally. We're not built to do the same work day after day, a rest day is beneficial.


Monitor urine color. (pee in an empty clear bottle) If darker than light apple juice, drink more water. Brown apple juice is too dark.

I drink 2 to 3 ounces of water per mile. Maybe 0.5 to 1 ounces of Gatorade type drink per mile - on the high end on hot days. I sweat most of that out on 100 mile bike rides. I rarely stop to pee.

I have tried almost everything for food. Chocolate is always a mess. I rode 200 miles on peanut butter and jelly sandwiches. Felt great. My favorites are bags of cookies. I did 100 miles on two bags of cookies. Better than Clif bars.

30+ years of long distance riding


This looks much more like overheating of the head. I suggest checking your helmet, for a slow (climbing) and hot summer ride it must be well ventilated and not black.

  • So you're suggesting heat stroke more than dehydration?
    – Criggie
    Commented Jan 20, 2022 at 10:56
  • 1
    I think yes. I agree with other posts here does not look like dehydration. On rough terrain, he may not had adequate speed for cooling by front wind.
    – nightrider
    Commented Jan 21, 2022 at 7:51

The answer for hydration for any sport is almost always "drink when you are thirsty."

That's it.

Headache that long after a modest effort is not likely to be dehydration, and there are too many other possibilities to list. Humans have developed over millennia a very good system to avoid dehydration -- thirst. There's an entire book on the development of the dehydration myth in sports (by Tim Noakes) and he goes into great detail about how it came about -- TL/DR the sports drink industry pushing the idea that performance is related to keeping your water topped off.

Salt is another confounding variable -- it was originally added to gatorade to help the solution clear the stomach, not to "replace" what was lost in sweat. (Again, see Noakes. The human body reduces salt output as necessary during heavy sweating.)

Urine color isn't an indicator, nor is urine volume. (Dangerously over-hydrated people suffering from hyponatremia often stop urinating!)

I'm surprised there's still such a paranoia about dehydration as (awful) experiments from long ago (army soldiers left in the desert with no water) showed that they do not dehydrate for days. True, they stop doing any work, and they don't feel great, but it's not the life-threatening condition everyone makes it out to be during a heat wave.

The life-threatening condition is heatstroke, and drinking cannot help there. Drinking doesn't cool you down (and if it's hot enough, neither will sweating). Shade or cooling your body are the only help for that. During super hot weather here, I always run alongside a creek in case I need to drop into it for a cool off.

I read the research (and Noakes) intensely on this issue a few years ago when I was regularly running marathons (15 or so per year) and ultra marathons, most of them in very hot and humid weather. The answer was always, drink when thirsty, and eat along the way. I would regularly lose 5-8% of my body weight in a day of hot mountain training (10-15 pounds) despite having drunk as much water, soda, and gatorade as I wanted. (refilling water at creeks and stopping at country stores when possible).

Losing a ton of water (and spent energy, which is stored with water in cells, IIRC) without any performance penalty is not an unusual occurrence, and again Noakes' book notes that high performance runners generally don't drink all that much -- just to thirst. And years ago, they drank even less. (Those that skipped calories entirely often fared worse, however.)

Hydration's easy. Sip from that bottle. Buy a soda. Do not force hydration -- hyponatremia is life threatening, immediate, and once it hits, it can require medical attention to reverse. (Worst of all, the symptoms are similar in many ways to heat exhaustion, so the casual first responder may tell you to drink, or stick an IV in you. Medics have killed people this way, which is why blood tests are now standard for dizzy participants at the end of hot-weather marathons.)

Food can be harder. The working body doesn't digest well, and everyone's preferences and tolerances are different. (That's why the food tables at an ultra-marathons look like a crazy junk-food buffet.)

In my own experience, it took a much longer time to build up a sufficient glycogen base that I could run an entire marathon without eating and without bonking. I was never able to push that to 50k without eating.

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