Menstruation and DLW

Last August, we established that energy expenditure doesn’t change over the course of the menstrual cycle (Energy Expenditure and Menstruation). From month to month, your body wants to be as consistent as possible, as dictated by the constrained energy model (Pontzer 2018). Even if RMR increases for a period of time throughout the menstrual cycle, expenditure in other pools will decrease in order to compensate and keep your burn as stable as possible.

Calorify uses double labeled water to measure total energy expenditure and estimate total energy intake, both with gold standard accuracy. The expenditure calculation is as simple as using Calorify’s at-home kit: a sip of water and three urine samples. The intake estimation combines the expenditure measurement with a user-reported trend of weigh ins. This method is superior to traditional calorie counting as it does not suffer from systematic undercounting and underreporting biases (reference). It can, however, be influenced by external factors driving weight change such as salt intake, creatine supplementation, and hydration level, so it’s important to keep these consistent throughout the data collection period.

So, while the menstrual cycle doesn’t impact the gold standard measurement of total energy expenditure, the cycle could impact total energy intake (TEI) and body composition calculations if the effects of fluid retention are particularly noticeable.

In a perfect world, if your weight increases throughout your test, there has been a positive change in your energy stores, and therefore you’ve eaten more than you’re burning. However, fluid retention, or bloating, during menstruation shows up as “weight gain” because your body is holding on to water (so you have more water weight). White et al. 2011 did a study on self-reported fluid retention and found that it was greatest on the first day of flow, and lowest throughout the mid-follicular phase (see introduction to this blog post for more on cycle phases).

Days of the menstrual cycle vs. hormone levels

So, if over the course of a week you start to hold onto more fluid, like leading up to menstruation for example, your weight will appear to artificially increase (I used the word artificially here because while the scale is indeed going up, it isn’t traditional weight gain as in stored energy). TEI will look artificially high then because the calculation is based on change in weight over the course of the test.

Similarly, body composition can be impacted by the increase in water weight, making you appear to have more lean body mass (because water is stored in places like muscle, not fat).

What does this mean for when you should take a Calorify test? The answer is you can still test at any time.

The gold standard measurement of total energy expenditure is not impacted by fluid retention or the menstrual cycle. If you are menstruating and notice that your weight had been increasing over the course of your test, work with your provider to see how your longer term weight trend can be used with your Calorify results to get a better picture of your energy intake. The best way to increase confidence in your TEI is to provide us with as many weights as possible.

For more information, you can always email support@calorify.com!