Why do some women gain weight on BC yet weight gain is due to excess calorie intake

264 viewsBiologyOther

Hello! as to why some women gain weight when they go on hormonal birth control?

I’m a big fitness person and believe that calories in v calories out is what makes you put on weight. If someone is still working out and their diet hasn’t changed but they began hormonal birth control, why are they putting on weight? How does this happen?

I’m genuinely curious and would love some insight. Thank you.

In: Biology

12 Answers

Anonymous 0 Comments

This is an issue of no simple explanation is entirely accurate with regard to weight.

Calorie in vs calorie out is mostly correct… in regard to weight based on stored fat. But there are other ways that people can gain weight.

Water retention is a real thing. Your body has systems in place that determine how much water you maintain in your body. Hormones and high salt intake can cause your body to store more water.

Birth control pills can cause a person to retain more water and thus put on weight.

Anonymous 0 Comments

Calories out are partly based on your metabolism. If your BMR goes down, you burn fewer calories passively.

Anonymous 0 Comments

The primary mechanism is that people aren’t accurately measuring or estimating the amount of food they eat.

Anonymous 0 Comments

I suppose it could be changing BMR. It’s likely that their calorie intake changed but changes in hormone might be impacting appetite and cravings.

Anonymous 0 Comments

It’s still calories in vs. calories out, but what you’re not seeing is that the “Calories Out” side of the equation is mostly driven by your metabolism, not your exercise routine (with the obvious caveat for someone who is exercising multiple hours every day).

All animals burn a certain number of calories every day just to stay alive. For warm-blooded big-brained animals, that number is quite high. For an average-sized woman, probably 1400-1800 calories per day are consumed just to maintain body temperature, brain activity and basic functions. These activity levels are largely controlled by your hormones.

When you go onto hormonal BC, this disrupts the natural ebb and flow of hormones that accompanies the menstrual cycle. This, in turn, impacts the baseline metabolism of the woman in question, so her body is no longer burning as many calories just to keep her alive. So if she doesn’t adjust either her activity level or her diet, she’ll still have the same “Calories In” value, but her “Calories Out” value will drop.

It’s the same reason that it’s more difficult for people with certain medical conditions (hypothyroidism, for example) to lose weight, especially if we’re not medicated properly. Our bodies don’t burn enough calories, so it’s harder for us to reach a calorie deficit. We’re not more efficient with our calories or anything like that – we just don’t burn enough of them. It’s like trying to run a car with an undersized engine.

Anonymous 0 Comments

More than likely it affects appetite. Just like appetite often increases in pregnancy or people get cravings for sweets during their period, any hormonal change can affect appetite. Unless they are meticulously weighing their food, Someone may think that that their diet hasn’t changed at all, but they’re actually taking a bigger portion at dinner or eating a little more chocolate than before, and it adds up.

Anonymous 0 Comments

I retained water weight on BC. As soon as I stopped, I would look like I lost five pounds. Nothing changed. I was also a size 2 and ran daily for most of my adult life and was always at the gym on my days off.

Anonymous 0 Comments


Anonymous 0 Comments

Medications don’t cause you to gain weight(body fat). They can cause you to retain more water which can seem like weight gain. They can also cause lethargy which can lower your caloric expendature. In the second case you’re eating the same or more calories, but moving less.

Anonymous 0 Comments

“Weight gain is due to excess calorie intake” is an oversimplification. It’s true, more or less, but it doesn’t capture the nuances of nutrition and the human body. Even my explanation below isn’t close to complete, just focused on resolving your question.

So let’s start with the absolute basics. Why do you eat? Overthink it and you might say that you eat because your body needs food to function, but that’s too far removed from the question. I didn’t ask why humans eat, I asked why *you* eat. And the answer to that is obvious: because you’re hungry.

Question number two: Why are you hungry? Because the balance of chemicals in your body has shifted, and your stomach and brain interpret that to mean you need food. Maybe even a certain type of food. And as you build habits in both what and how you eat, your body responds by adjusting its baseline. Eat an apple and you’ll feel more “full” than if you eat the equivalent volume in Jolly Ranchers. And after that apple, you’ll take longer to feel hungry again. But with the candy, not only will you feel hungry sooner, you’re training your body to *expect* that rapid infusion of calories. Do it often enough and you’ll have a physiological urge to eat more sweets. Its habit forming. Literally. And it’s driven by your body’s hormones.

Question the third: How are those calories stored in your body? Obviously there’s a division between fat and muscle, but how does your body decide which to build and where? Cardio to burn calories. Weights to build muscle. Sit on your ass to get fat. But how does your body know when to do each one? Again, hormonal signals drive the response. Someone with more of one hormone might add muscle mass more quickly than someone with less of it, even if you’re working out the same amount. And between those two people, the excess calories go to fat. Is it subcutaneous or visceral fat (under the skin or around the organs)? Hormones drive it.

Question IV: Now that we know why you’re eating a lot, and choosing unhealthy foods when you do… why don’t you burn it off with exercise? Well once again, hormonal cues can affect how active a person is. Are you sitting still when you’re sitting down, or moving around? When you have free time, do you feel like moving or relaxing? Like with eating, it’s easy to say that you can “choose” one or the other, but your body has a lot of weight on the scale (heh). You might *know* that exercising is good for you, but knowing something doesn’t necessarily translate to action. Again, hormones can push you one way or the other. Building up good habits helps regulate those hormones and prompt you to keep it up, but that can go haywire because of how we answer…

The final question: How does birth control work? It shifts the balance of hormones in your body. Shifting that balance can, depending on what you’re taking and how your body accepts it, affect your hunger, what you’re hungry for, how your body processes that food, where it stores fat, and your own baseline energy levels. Shift the levers wrong and you’ll gain weight.

*Can* you stay skinny despite all that? Sure. It’s just a whole lot harder, and the people shouting “calories in:calories out” are making things harder by ignoring how the human body actually functions. It’s not a simple machine with a fuel gauge and a meter to measure output. People struggling with weight aren’t having issues with *math*.