Understanding Water Retention

One of the biggest concerns for women who are on a health and fat loss journey is WATER RETENTION!!

Are you struggling to understand this concept, too?

Good, you’re in the right place…

Let’s begin with the basics of fluid balance in a healthy human being.

Your body is made up of 60-70% of your body weight in WATER, so regulating salt and water is critical to maintaining optimal fluid balance. Optimal fluid balance is important because, without it, your nervous system stops functioning, thus your muscles stop contracting, and your heart stops beating.

So now do you believe me that this mechanism is, indeed, CRITICAL?

Ok, let’s move on…

If you think about it, our intake of salt and water varies pretty widely from day to day, but somehow your body is able to maintain a balance of electrolytes and water.

How so?

Well through an extremely intricate balance of hormones that act on filtration in your kidneys (this was by far the most complex topic in A&P, by the way).

But for simplicity, there are two main hormones responsible for fluid balance:

Aldosterone and Antidiuretic Hormone.

So real quick, Aldosterone is a steroid hormone that regulates the concentration of minerals (sodium, potassium, etc.) by retaining these minerals in the blood if the concentration is too low (or water concentration is too high).

Antidiuretic Hormone (vasopressin) works by retaining water in the kidneys rather than it being expelled through urine.
While these hormones are important, the hypothalamus (a region of your brain often called the “master controller”) regulates these hormones to fine-tune water balance at any given point in time. Even more important, the kidneys are the organs that do all the work of expelling or retaining water and electrolytes as these hormones bind to receptor sites in the kidney tubules.

OK, enough of the physiological background…how does this apply to REAL LIFE?

So let’s say you went to a Chinese restaurant last night and you had an entire plate of rice, vegetables, and chicken full of Yum Yum and Soy sauce. This meal most likely had way more sodium in it than you usually take in during the day. So when you digest and absorb the food and minerals, your brain takes samples of your blood and tests it for the concentration of substrate, in this case, the electrolyte sodium.

After that super-sodium meal, your blood is going to be VERY concentrated with sodium and chloride ions, so your hypothalamus sends a signal to release an Antidiuretic hormone which is going to act on the kidneys to RETAIN water. So you’ll notice after a night of salty foods, the next morning you haven’t gone to the bathroom and you are up 3+ pounds. You might be outraged, but this is your body’s way of managing fluid balance to keep your cells from shrinking or blowing up via osmotic pressure imbalance…pretty important, right?

So again, one of the biggest concerns for women, especially those on a fat loss journey, is seeing the scale fluctuate up and down over the course of the week. Well, now you have begun to understand one of the major players in why that occurs!

Other players include carbohydrate intake and glycogen storage, stress hormones, and estrogen and progesterone.

Side note, studies show that estradiol lowers the operating point for osmoregulation of Antidiuretic hormone. What this means is that blood plasma volume is increased by water retention! So ever notice girls, that when you experience PMS, the scale increases 2-4 lbs that week? Bingo. You might also notice that you are your “lightest” the week right after your period. That is because progesterone, which acts as a diuretic, is at its peak at this time.

Thanks, ladies!

Stachenfeld, Nina S. “Sex Hormone Effects on Body Fluid Regulation.” Exercise and Sport Sciences Reviews. U.S. National Library of Medicine, July 2008. Web. 22 Dec. 2016.
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