Birth Control Pills and Weight Gain
Do oral contraceptives cause water retention and how much?
Estrogen in high doses is known to cause weight gain especially that due to fluid retention. The more estrogen there is in a pill, the more tendency to gain weight such that a 50 mcgm pill will result in more weight gain than a 35 mcgm pill.
The mechanism of action is probably direct stimulation by the estrogen in pills of kidney substances called renin-angiotensin that cause water retention. The water retention then causes sodium (salt) retention. A lower estrogen level pill, e.g., 20 mcgm, will help reduce weight gain due to fluid retention.
This was confirmed in a more recent study with 30 mcgm pills in which there was essentially no difference in weight gain or weight loss between the placebo group and the oral contraceptive group. Again, however, 30% of these women had a weight gain of more than 1 lb. but the net result was the same in the control group. Those who did have weight gain had increased fat but no difference in fluid retention amounts indicating that fluid weight gain may be less of a problem with the newer, lower estrogen pills.
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