Q: I know we have two kidneys, but what exactly do they do again?
A: Your kidneys are amazing. They do many things, but in short: they filter your blood. Check out the picture below. Blood enters your kidney "dirty" (think about how your motor oil gets dirty), is passed through a series of microscopic filters called glomeruli, and is separated into two products: clean blood and urine. The clean blood goes back to the rest of your circulation, and your urine heads to your bladder until you get a chance to pee. You're kidneys also keep your salt/electrolyte balance in check, as well as your total body water volume (dehydration versus swollen states). This in turn has a significant effect on your blood pressure. Here's a fun fact: your kidneys filter 180L (about 48 gallons) of fluid every day!! That's nearly 5 Miata tanks worth of gas every day!
Q: Is decaffeinated coffee a diuretic?
A: Not exactly. It is the caffeine in coffee that makes it a diuretic, so decaffeinated coffee wouldn't technically be considered one. Of course, large volumes of any liquid can be considered a diuretic because of the resulting increase in volume loss (i.e., you pee a lot).
Q: Will drinking a whole lot of water before going to bed counteract the effect of drinking a little too much alcohol in the evening (no headache in the morning)?
A: To some extent, yes. First, let me introduce you to our friend, anti-diurectic hormone, ADH (aka vasopressin). This is a hormone in your body that comes to your rescue when you are dehydrated. It comes from your brain and heads down to your kidneys where it essentially makes them more effective sponges - that is, it helps your kidneys hang on to as much water as possible and make your urine very concentrated. One of the major effects of alcohol is that it blocks ADH. Without the ability of your kidneys to suck up extra water, you end up just peeing our very dilute urine - this is dehydrating, and one of the reasons why you have a headache in the morning. I'm not sure about other things in alcoholic beverages that might contribute to the hangover, but certainly feeding your body some water before you go to bed is a good start!
Q: How can a long-distance runner know how much water is enough to drink, and how much is too much?
A: This is a great question. Previously, people were concerned about long distance runners becoming dehydrated. Now, there is a great concern that runners are over-hydrating. Drinking too much water results in hyponatremia - that is, the relative concentration of sodium (Na) in your system is too low. This may not seem like a big deal, but a 28-year old woman died in 2009 in a radio-hosted water drinking contest to win a Nintendo Wii.
You can read about it here. I'm not sure that there is any conclusive advice, but my impression was that it's recommended that runners pay attention to their own thirst, and let that guide their water intake. Also, for experienced long-distance runners it can be informative to weigh yourself before and after long runs when you're training - that way you know if the amount of water you're drinking during your run is causing you to gain weight (which you shouldn't be).
Q: How bad is it to have consistently foamy urine?
A: Firstly, it's normal to have a few bubbles. This is caused by protein in the urine. The filtration system of your kidney is very good at preventing proteins from escaping in your pee (you don't want to lose your protein!) but very, very small amounts can pass through. The proteins act like a detergent, which is why you sometimes see bubbles. What might be of concern is if the bubbles are significant (like when you flush, there are still bubbles clinging to the inside of the toilet). When a significant number of proteins are coming through your pee (this is called proteinuria) it often suggests that the filtration barrier has been upset in some way. This is no bueno, and I would encourage asking your physician about this. Proteins passing through the filtration system is incredibly damaging and taxing on your kidneys - it doesn't always result in irreversible damage, but it certainly can.
Q: Why does it seem like I gain weight after eating a salty meal?
A: Because you do! Your body is excellent at maintaining specific concentrations of salts in your blood and in your tissues - it has to in order to keep you alive! If the concentration changes, your body will adjust to accommodate. For instance: if I head to my local Brazilian steakhouse, have a beer, then pound a solid serving of ice cream, I'm going to be REALLY thirsty. So I'll drink lots of water. First and foremost, your body wants to make sure that the salt concentration stays the same, so it will hang on to the water that followed the salty intake (thus, the extra pounds on the scale). When you stop consuming the salt, your body will eventually catch on and realize that it's hanging on to extra water (and salt), and you'll let go of it. This is why patients with high blood pressure are asked to follow a low-salt diet - high salt intake = high fluid intake = high volume and blood pressure.
Q: Is it true that more and more younger folks are suffering from kidney stones? What's causing it? Is there anything a person can do besides getting them taken out by a doctor?
A: It is true that kidney stone prevalence is on the rise, and while the cause is not entirely known, it's thought that the obesity epidemic (in adults and children) is one of the major culprits. There is something about being overweight that changes the content of urine, making it more susceptible to forming stones (sorry for the vague answer - I wasn't able to determine a more conclusive stance). The bad news is that there aren't any at-home treatments; the stones will not just disintegrate on their own. Sometimes if they're small enough they may not cause problems and just pass in time, but there is also a risk that they will continue to grow and cause problems (painful problems). It's interesting, apparently not many people have looked too closely into kidney stones - the lecturer was recruiting big time. I guess kidney stones just isn't as sexy?
Q: With all of the different advertisements regarding what we should be drinking…well… what should we be drinking?
A: Water! This is a fairly difficult question to answer - many people will have different opinions (which reminds me - whenever you get advice from someone, ask for disclosures - you never know when someone is getting paid to say certain things). When you're not sweating, water is a perfectly excellent beverage to sip throughout the day. If, however, you're in a situation where you may be sweating bullets on a regular basis (competitive sports, combat, etc), then you may want to drink something with some electrolytes. Gatorade used to be pretty high in salts (this is good) but that meant it was loaded with sugar so that it tasted okay (this is not good). They have since tapered both ingredients now. The nephrologist that I spoke with said a watered down gatorade would be better than water in high-stress/sweat situations. As far as coconut water goes, it is very high in potassium (some are 15% of your daily recommended value). Potassium, like other electrolytes, is critical to health, but also results in devastating effects if it strays too high or too low (heart attack and death in serious extremes). Having a coconut water isn't going to kill you, but guzzling them to "replenish" what you've lost through sweat isn't a great idea. And on top of that, not all sweat is created equally - different levels of effort/stress result in different amounts of salt loss in your sweat (going for a brisk walk will produce less salty sweat than deadlifts and bench presses for 3 hours.
