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Women Are Not Small Men—Especially When It Comes To Obesity Research

Women Are Not Small Men—Especially When It Comes To Obesity Research

Let’s delve into the nuances of women's health research, particularly concerning investigations into treatments for overweight and obesity.

Obesity and overweight—gender similarities and differences

Let's start with some numbers. By 2022, roughly 8 billion adults globally were grappling with being overweight, and a staggering 890 million were classified as obese.1 Interestingly, slightly more women* are obese compared to men, according to World Health Organization data.1 Regionally, about two-thirds of the Americas’ population is dealing with overweight issues.1 These statistics reflect a concerning trend of increasing body mass index (BMI) over recent decades. In the USA, the Centers for Disease Control reported that in 2022, there were 22 states where at least 35% of adults were obese (BMI of 30 or more), compared to 19 states only a year before that—and no states 10 years earlier!2 When researchers analyzed 60 years of data about overweight, obesity and severe obesity (BMI of 40 or more), they discovered that compared to men, fewer women are overweight (BMI 25-29.9).3 And while women used to have higher levels of obesity compared to men, both sexes are now similar—but severe obesity is more common in women.

Another study demonstrated that over 10 years, US women gained about twice as much weight as men, indicating potential factors such as pregnancy-related weight gains and differences in physical activity levels between genders.4 However, it's worth noting that the impact of hormonal changes on weight gain —for example, during the menstrual cycle or menopause—wasn't thoroughly explored in these findings.

We eat what we are

Could there be other reasons that women are more likely to gain significantly more weight than men over time? It turns out there are: researchers have observed distinct variations between men and women in food cravings, which can affect obesity.5 Women tend to experience stronger and more frequent cravings for food (especially sweet treats like chocolate) compared to men, who lean towards savory cravings. So, it turns out, it’s not just true that “we are what we eat” but it seems we also eat because of what we are.

The role of hormones

Researchers have attributed these differences in cravings (both how much and what we eat) to the changes in sex hormones as they rise and fall during the menstrual cycle. For instance, estrogen reduces appetite in both men and women, (yes, men also produce estrogen). As estrogen levels drop after ovulation, women eat more with strongest cravings just before their period, particularly for sweet foods (notably, chocolate), eating on average almost 250 calories more a day.5,6 Over a year, that could pack on an additional 10-20 pounds (4.5-9 kg)!5 And as they enter menopause, the drop in estrogen accounts for the weight gain that many women experience. Figure 1 shows how hormone levels and food cravings change during women’s menstrual cycles.5

Figure 2: Food craving during menstrual cycle changes as ovarian hormone levels fluctuate. From Hallam, et al, 2016.6 Used with permission.5

Clinical research differences: “women are not small men”7

When it comes to clinical research, there's a notable gap in addressing gender differences. Despite women being more prone to weight gain and severe obesity compared to men, research examining weight loss medications overlooks potential gender-specific effects. For example, in the studies that led to the use of semaglutide (Wegovy/Ozempic) and tirzepatide (Zepbound/Mounjaro) for weight loss, most of the participants were women—yet no information was published in either case about whether these two medications affected women and men differently.8,9 This reflects a broader issue of gender bias in health research, where the male body is often considered the default in scientific investigations.10 What’s more, women’s health concerns are underfunded compared to men—and not just those that affect only women (such as pregnancy or gynecological issues), but also how diseases that occur in both sexes affect women differently.10

Promising developments

However, there are changes afoot from some obesity researchers. Scientists from New Zealand’s Plant and Food Research conducted two separate trials of Amarasate® in fasting men and women. (Amarasate® is the active ingredient in the weight loss supplement, Calocurb®). This was by no means an easy thing to do... knowing that the menstrual cycle has a role in food cravings, the women enrolled had to return on the same day of their menstrual cycle for each stage of the study (and the same day of the week!). But the extra effort was worth it, because the researchers demonstrated that there were gender differences in Calocurb®’s effects. After taking Calocurb® towards the end of the fasting time, the women showed no increase in hunger at 24 hours compared to the starting point, their overall hunger was down 30% and their overall cravings by 40% (compared to placebo).11 Men also showed a benefit, but still had some hunger at 24 hours and their overall hunger reduced by 25%.12 It seems that women were more sensitive to the affects of Calocurb® during a fast. These findings underscore the importance of considering gender-specific factors in obesity research and treatment.

While changes are being made in acknowledging gender differences in obesity research, there's still much ground to cover. Increased funding and attention towards women's health research, as demonstrated by recent initiatives in the USA,13 offer hope for a more inclusive and effective approach to combating obesity and related health issues. Hopefully that means more researchers will acknowledge that women are indeed, not just small men! Here's to a healthier future for all of us!

*For the purposes of this article, women include cis women and people assigned female at birth; men include cis men and people assigned male at birth.

- Written for Calocurb by Dr. Tracey Lambert

References:

  1. Obesity and Overweight. www.who.int. Published March 1, 2024. Accessed March 7, 2024. https://www.who.int/news-room/fact-sheets/detail/obesity-and-overweight#:~:text=In%202022%2C%201%20in%208
  2. CDC Newsroom. CDC. Published September 21, 2023. Accessed March 7, 2024. https://www.cdc.gov/media/releases/2023/p0922-adult-obesity.html
  3. Fryar C, Carroll, M, Afful, J. Prevalence of Overweight, Obesity, and Severe Obesity among Adults Aged 20 and Over: United States, 1960–1962 through 2017–2018. NCHS Health E-Stats; 2020. Accessed March 7, 2024. https://www.cdc.gov/nchs/data/hestat/obesity-adult-17-18/obesity-adult.htm#1
  4. Tucker LA, Parker K. 10-Year Weight Gain in 13,802 US Adults: The Role of Age, Sex, and Race. Papadia FS, ed. Journal of Obesity. 2022;2022:1-10. doi: https://doi.org/10.1155/2022/7652408
  5. Hallam J, Boswell RG, DeVito EE, Kober H. Gender-related Differences in Food Craving and Obesity. The Yale Journal of Biology and Medicine. 2016;89(2):161-173. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4918881/
  6. Buffenstein R. Food Intake and the Menstrual Cycle: A Retrospective Analysis, With Implications for Appetite Research. Physiology & Behavior. 1995;58(6):1067-1077. doi: https://doi.org/10.1016/0031-9384(95)02003-9
  7. Pérez L, Francis T. “Women Are Not Small Men”: The Global Economy Will Miss Out on $1 Trillion Annually by 2040 if We Don’t Close the Gender Health Gap. Fortune. Published January 17, 2024. Accessed March 3, 2024. https://fortune.com/2024/01/17/women-global-economy-will-miss-out-on-1-trillion-annually-by-2040-gender-health-gap-perez-francis/
  8. Wilding JPH, Batterham RL, Calanna S, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity. The New England Journal of Medicine. 2021;384(11):989-1002. doi: https://doi.org/10.1056/NEJMoa2032183
  9. Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide Once Weekly for the Treatment of Obesity. The New England Journal of Medicine. 2022;387(3). doi: https://doi.org/10.1056/nejmoa2206038
  10. Ellingrud K, Pérez L, Petersen A, Sartori V. Closing the Women’s Health Gap: A $1 Trillion Opportunity To Improve Lives and Economies. McKinsey. www.mckinsey.com. Published January 2024. Accessed March 6, 2024. https://www.mckinsey.com/mhi/our-insights/closing-the-womens-health-gap-a-1-trillion-dollar-opportunity-to-improve-lives-and-economies
  11. Walker, E.; Lo, K.; Gopal, P. Gastrointestinal Delivery of Bitter Hops Extract Reduces Appetite and Food Cravings in Healthy Adult Women Undergoing Acute Fasting. Preprints 2023, 2023090416. https://doi.org/10.20944/preprints202309.0416.v1
  12. Walker E, Lo K, Tham S, et al. New Zealand Bitter Hops Extract Reduces Hunger During a 24 h Water Only Fast. Nutrients. 2019;11(11):2754. doi: https://doi.org/10.3390/nu11112754
  13. Superville D. Jill Biden Announces $100 Million for “Life-Changing” Research and Development into Women’s Health. AP News. Published February 21, 2024. Accessed March 4, 2024. https://apnews.com/article/jill-biden-research-womens-health-arpah-shriver-149bf923d666bb980631185c0626a50e