I've been talking about hydration a lot recently. Both with my clients and in day to day conversation, which is kinda weird. Also, the topic isn't exactly dinner party conversation, but as a registered dietitian, I find myself talking about strange things with strangers all the time; it becomes normal to me!
There are many different opinions on how much one should drink in a day, and also where those fluids come from, and it's hard to find someone walking around these days who isn't holding a water bottle. Hydration is hip. But how much fluids do we need in a day? Where should those fluids come from? Doesn't caffeine dehydrate you? I'm glad you asked.
Everyone's fluid requirements are different, therefore, it is difficult to give a stock answer. The old '8 glasses a day' is too generic to be of any help, since my glasses are likely not the same size as yours (however, I did buy my glasses at Ikea, so it's likely most of the planet have the same glasses as I do). That statement is good, in that it encourages people to think about how much they drink, but it's not much good for anything else. Your daily fluid requirement is multifactorial. It depends on your weight, your activity during the day, how much you sweat, how dry/moist the air is where you live, and what food you eat. So an athlete who works out twice a day will need much more fluids than someone who weighs the same and sits at a desk all day. Also, someone who weighs 170 lbs will need much more fluid than someone with the same activity who weighs 90 lbs. So how do you know how much you need? We'll talk about that in a little bit, stay tuned.
Fluids can be obtained from whatever source you like. Water is great, simply because it's low (zero) calorie and what your body needs, but for those people who don't like water or enjoy other fluids, mix it up! Drink what you like! If we're talking only about fluid, we don't have to be too picky on what we put in our mouths. However, nothing in life is that simple. Most fluids (juice, coffee, milk) contain calories, so you need to watch you're not drinking too many calories during the day. Remember also that food has fluid within it. Most foods contain some fluid, at that counts towards your daily intake, but it can get tricky to figure out how much is in every kind of food. Generally speaking, fruit and vegetables have lots of fluid (think watermelon or celery) and prepared foods like soup obviously contain a lot of fluid, but they all count! So a big salad will provide quite a bit of fluid - that's less you need to drink! Typically, I encourage my clients to not worry about the fluid content in food, I suggest they aim to get their needs through drinking stuff, and count the fluid from food as bonus, but that doesn't always matter (it'll make more sense once I talk about that other thing I mentioned earlier).
Next up, caffeine! Everyone loves to hate it, or at least feel bad about loving it. Almost every time I ask a client about their coffee/tea intake, they look at me sheepishly while admitting they drink '3, maybe 4 coffees a day'. I don't understand why people feel so bad about drinking caffeine! Anyway....caffeine is a diuretic, meaning that it causes your kidneys to excrete more fluid than they would without it. We used to suggest that people should drink 1 glass of water for every caffeine-containing beverage to 'break even'. Meaning that they would have to drink 2 glasses of water for every caffeine-containing beverage to make headway in their hydration. Now, at least in certain populations we've stopped saying that and count caffeine-containing beverages towards total fluid intake. The best answer I give about caffeine is that it's not quite the diuretic we once thought it was, but it should be limited in the diet for other reasons. If taken in excess it can cause cardiac arrhythmias (irregular heart beats), also the other stuff you put in your coffee (double double) can really add up calorically. So keep the caffeine-containing beverages occasional but enjoy them from time to time, or switch to decaf midday.
So, after all of this vague talk, it's time for the good stuff; how do you tell if you're adequately hydrated. You now know it depends on your size, activity, the food you eat and a million other factors, and that 8 glasses a day isn't an appropriate recommendation, but what is?
It's super simple. It's the colour of your urine! It's real-time feedback on how you're doing with hydration, and can help you fine tune it.
So, every time you use the washroom, take a look before you flush. Aim for a light yellow colour (2-3); clear (1, you can't tell you've peed) means you're over-hydrated and can take a break from drinking for a little while, dark yellow to brown (4-7) means you're dehydrated and need to drink something right away. It's as simple as that! No crazy equations, no looking up the fluid content of your favourite foods, no arguing whether your cup of coffee counts towards your daily fluid intake and certainly not worrying about how many standard-sized glasses you've drank in a day! Just take a look before you flush, and adjust.