BY: Jessica Baker, PhD
Date: August 31, 2015
New research suggests that the genetic influence on emotional eating—defined as eating in response to negative emotions—changes across the menstrual cycle.1 This follows up research findings that have already established that: 1) eating disorders are biologically-based disorders, with genetic factors influencing risk and 2) eating disorder symptoms fluctuate across the menstrual cycle.
Before diving more into these exciting research findings, it’s important to provide a bit of background. As mentioned, research has established that genetic factors (i.e., one’s genes) influence the risk for eating disorders—specifically 40-60% of the risk for eating disorders is due to genetic factors.2 Interestingly, these genetic effects only appear after puberty! This means that genetic factors may be minimally important for the development of an eating disorder prior to the onset of puberty but that after puberty, genes play a significant part in eating disorder risk. Even more interesting is that this finding parallels the increase in estrogen that occurs at puberty in girls. This has lead some to hypothesize that estrogen at puberty ‘turns on’ the genes responsible for eating disorders.3
Eating disorder behaviors such as binge eating and self-induced vomiting also fluctuate across the menstrual cycle.4 These behaviors tend to be more frequent during phases of the menstrual cycle when estrogen is low or progesterone is high. This fluctuation of eating disorder behaviors across the menstrual cycle is not all together surprising given that estrogen and progesterone play a role in regulating eating behavior. Specifically, estrogen decreases food intake and meal size and advances the onset of feeling full while progesterone increases food intake. However, unlike estrogen (which directly impacts food intake), progesterone seems to have an indirect impact on food intake such that it only increases food intake in the presence of estrogen by stopping estrogen from doing its job and limiting food intake (suggesting an interaction between estrogen and progesterone).
So, we know that genes play an important role in determining who may develop an eating disorder after puberty and that eating disorder behaviors fluctuate across the menstrual cycle in girls, but we don’t know whether the genetic influence on eating disorder behaviors changes across the menstrual cycle.
Because of the background just described, Dr. Kelly Klump and her colleagues embarked on a mission to examine whether the degree to which genes influence eating disorder behaviors changes across the menstrual cycle. To do this, Dr. Klump gathered information daily (for 45 days) from female twins including questions about eating behaviors and menstruation, and saliva samples to get estrogen and progesterone levels.
Why twins? Well, it is from twins that we are able to assess whether a trait is influenced by genetic factors. This is done by comparing traits in identical twins (who share 100% of their genes) and fraternal twins (who only share 50% of their genes—the same as non-twin siblings). If a trait is 100% genetic, then you’d expect both identical twins to have the trait and to be exactly the same on the trait because they share 100% of their genes. If identical twins are any less then 100% the same on a trait or both twins don’t have the trait, this means that non-genetic, twin-specific environmental factors (e.g., one twin experiences a trauma and the other does not) are important in influencing risk for the trait. We need fraternal twins as a comparison because being a twin comes with a lot of other experiences (having a sibling the exact same age as you) and events (being in the uterus with someone else) that non-twin siblings do not have. Additionally, if identical and fraternal twins exhibit a trait in the same way, this means that environmental experiences shared by the twin pair (e.g., parental divorce) are important in the risk for the trait.
By obtaining all of this information in a sample of female twins, Dr. Klump was able to assess whether the genetic risk for emotional eating changes across the menstrual cycle. And, as mentioned at the outset of this blog, the degree to which genes influenced emotional eating did in fact change across the menstrual cycle. Specifically, the genetic risk for emotional eating during pre-ovulation—when estrogen levels are high and progesterone levels low—was low, estimated at 20% whereas at post-ovulation—when estrogen levels are low and progesterone levels are either high or low—the genetic risk for emotional eating doubled to 40%. This also means that non-genetic/environmental factors were important in the risk for emotional eating during pre-ovulation.
After reading this, you’re probably asking yourself why is this important? Well, most importantly, this provides insight into why we see a fluctuation in eating disorder symptoms across the menstrual cycle. For example, pre-ovulation is the phase of the menstrual cycle when eating disorder behaviors are least frequent. Dr. Klump suggests her findings may indicate that the risk for emotional eating during pre-ovulation is lower because genetic factors are low. This information can also be useful in regard to treatment. Treatment providers may be able to pinpoint specific days of peak risk for these behaviors, allowing for more “menstrual phase-specific” individualized treatments. However, this is the first study of its kind and we need follow-up studies to confirm these results and to further address how we can use this information to better prevent and treat eating disorders.
- Klump, K.L., et al., Changes in genetic risk for emotional eating across the menstrual cycle: a longitudinal study. Psychological Medicine, 2015: p. 1-11.
- Trace, S.E., et al., The genetics of eating disorders. Annual Review of Clinical Psycholology, 2013. 9: p. 589-620.
- Klump, K.L. Puberty as a critical risk period for eating disorders: a review of human and animal studies. Hormones and Behavior, 2013. 64(2): p. 399-410.
- Baker, J.H., S.S. Girdler, and C.M. Bulik, The role of reproductive hormones in the development and maintenance of eating disorders. Expert Review of Obstetrics & Gynecology, 2012. 7(6): p. 573-583.