Fat Loss & Libido

Dropping body fat leads to a series of different benefits, but in what way does getting leaner help or hinder sex drive? In this article, we will investigate the evidence on how dropping body weight impacts our sex drive – let’s dive in.

What is Sex Drive/Libido?

Sex drive, also referred as libido, is the urge to have sex or seeking sexual contact [1].

Weight Loss & Sex Drive, Erectile Dysfunction

Losing weight, if you are overweight, or even normal weight and dropping a few kilograms, is largely seen as beneficial to sex drive and erectile dysfunction; as weight decreases, sex drive increases and erectile dysfunction decreases [3][4][5][6][7][11][13]. If you are already at a low body fat (guessing, 8-10%, in men, or lower), there is small amount of evidence that caloric deficits and consequentially more fat loss can decrease sex drive, but the evidence is weak or speculative [2][5][12].

Understanding the 

Physiology

This is a broad topic, as weight loss, caused solely by calorie restriction, can come in a variety of forms (low dietary fat, low carbohydrate, low protein, etc.). Not only that, although the focus is often on endocrine factors, there could be others that could come into play. That said, a few of the primary culprits are, indeed, endocrine in nature. The one that is most discussed is testosterone, but there are a few others to consider – which we will do shortly.

Testosterone does have an impact on libido, and it is changed with caloric restriction leading to weight loss [4][7][8][9][10][11][12][14][16][17]. In some cases, testosterone increases – likely, because those individuals are either overweight or normal weight, but have a higher body fat percentage than desirable. Then, what is it about body fatness that impacts testosterone?

The chief culprit is the hormone leptin, which is often immediately thought of when relating anything to adiposity and energy regulation within the body. Well, the idea is far from farfetched as low leptin levels directly reduce the hypothalamus’ release of gonadotropin stimulating hormone, and reduces the release of luteinizing hormone; this directly impacts sex hormones in the ovaries and testes [20][21][22]. Interestingly, leptin affect on luteinizing hormone may also be more direct by interacting with the pituitary gland, directly [22]. Conversely, adiponectin, another adipocyte centric hormone, in higher concentrations (unlike leptin) also reduces luteinizing hormone release by binding the hypothalamus and pituitary gland [22].

Clearly, leptin likely plays a major role in sexual desire and function, but why would weight loss lead to decreases in libido for some and an increase for others? The answer could be due to increased leptin levels in more overweight individuals to the point that those individuals, even with similar or greater weight loss still maintain higher leptin levels compared to lean or extremely lean individuals; essentially, there is sufficient leptin in circulation to maintain the synthesis and release of gonadotropin releasing hormone, and ultimately, luteinizing hormone [23][24].

 

Alternatively, as cortisol also increases with extreme caloric restriction, this has also been associated with decreased libido and erectile dysfunction [25]. However, there are also instances wherein cortisol stays stable (more long term, moderate deficits), yet free cortisol increases by a function of reduced cortisol binding globulin, leading to more bioavailable levels to act in the body [26]. Cortisol modulates the already poor release of gonadotropin releasing hormone by inhibiting the responsiveness of the pituitary gland to gonadotropin releasing hormone – leading to further decreases in luteinizing hormone and eventual sex hormone synthesis [27].However, how does testosterone (or other androgens) lead to changes in libido?

One of the mechanisms is thought to run through testosterone’s role in increasing the production of nitric oxide in the penis [28]. Another, more closely linked to sexual desire, is an intracrine mediated system wherein the neural cells will generate androgens, acting as a transcription factor in the genes of those same neurons [29][30]. Also, as testosterone is not the primary driver of sexual desire in women; the more abundant hormone estradiol/estrogen may play a more important role in a similar capacity [30][31]. Estrogen likely acts on the central nervous system (in an endocrine and, potentially, as an intracrine), as well as does contribute to vaginal readiness for sex by increasing lubrication [31].

Summary

While we cannot say the mechanisms explained in this article are all encompassing, they do offer some answers as to why some people lose their sex drive when dropping body fat and others gain greater sex drive and sexual function from dropping body fat. One of the main culprits is leptin differences between overweight and lean individuals, its impact on our sex hormones, and how those sex hormones communicate with our sex organs, as well as our brain (exciting it, for example). This is one of several mechanisms implying an endocrine action, but intracrine neuron signaling can also affect sex drive and sexual arousal. Overall, the topic is complex and likely encompasses more variables than those discussed.

References
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[12] Strauss, R. H., Lanese, R. R., & Malarkey, W. B. (1993). Decreased Testosterone and Libido With Severe Weight Loss. The Physician and Sportsmedicine, 21(12), 64-71. doi:10.1080/00913847.1993.11947613

[13] Moyad, M. A., & Park, K. (2012). What do most erectile dysfunction guidelines have in common? No evidence-based discussion or recommendation of heart-healthy lifestyle changes and/or Panax ginseng. Asian Journal of Andrology, 14(6), 830-841. doi:10.1038/aja.2012.82

[14] Ramasamy, R., Schulster, M., & Bernie, A. (2016). The role of estradiol in male reproductive function. Asian Journal of Andrology, 18(3), 435. doi:10.4103/1008-682x.173932

[15] Słuczanowska-Głąbowska, S., Laszczyńska, M., Piotrowska, K., Grabowska, M., Grymuła, K., & Ratajczak, M. Z. (2015). Caloric restriction increases ratio of estrogen to androgen receptors expression in murine ovaries - potential therapeutic implications. Journal of Ovarian Research, 8(1). doi:10.1186/s13048-015-0185-8

[16] Cangemi, R., Friedmann, A. J., Holloszy, J. O., & Fontana, L. (2010). Long-term effects of calorie restriction on serum sex-hormone concentrations in men. Aging Cell, 9(2), 236-242. doi:10.1111/j.1474-9726.2010.00553.x

[17] Helms, E. R., Aragon, A. A., & Fitschen, P. J. (2014). Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. Journal of the International Society of Sports Nutrition, 11(1). doi:10.1186/1550-2783-11-20

[18] Van Anders, S. M. (2012). Testosterone and Sexual Desire in Healthy Women and Men. Archives of Sexual Behavior, 41(6), 1471-1484. doi:10.1007/s10508-012-9946-2

[19] Mazur, A., Mueller, U., Krause, W., & Booth, A. (2002). Causes of sexual decline in aging married men: Germany and America. International Journal of Impotence Research, 14(2), 101-106. doi:10.1038/sj.ijir.3900833

[20] Odle, A. K., Akhter, N., Syed, M. M., Allensworth-James, M. L., Beneš, H., Melgar Castillo, A. I., … Childs, G. V. (2018). Leptin Regulation of Gonadotrope Gonadotropin-Releasing Hormone Receptors As a Metabolic Checkpoint and Gateway to Reproductive Competence. Frontiers in Endocrinology, 8. doi:10.3389/fendo.2017.00367

[21] Watanobe, H. (2002). Leptin directly acts within the hypothalamus to stimulate gonadotropin-releasing hormone secretionin vivoin rats. The Journal of Physiology, 545(1), 255-268. doi:10.1113/jphysiol.2002.023895

[22] Sam, A. H., & Dhillo, W. S. (2010). Endocrine links between fat and reproduction. The Obstetrician & Gynaecologist, 12(4), 231-236. doi:10.1576/toag.12.4.231.27614

[23] Verdich, C., Toubro, S., Buemann, B., Holst, J. J., Bülow, J., Simonsen, L., … Astrup, A. (2001). Leptin Levels Are Associated with Fat Oxidation and Dietary-Induced Weight Loss in Obesity. Obesity Research, 9(8), 452-461. doi:10.1038/oby.2001.59

[24] Al-Sultan, A. I., & Al-Elq, A. H. (2006). Leptin levels in normal weight and obese saudi adults. Journal of family & community medicine, 13(3), 97–102.

[25] Kobori, Y. I., Koh, E., Sugimoto, K., Izumi, K., Narimoto, K., Maeda, Y., … Namiki, M. (2009). The relationship of serum and salivary cortisol levels to male sexual dysfunction as measured by the International Index of Erectile Function. International Journal of Impotence Research, 21(4), 207-212. doi:10.1038/ijir.2009.14

[26] Yanovski, J. A. (1997). Differences in Corticotropin-Releasing Hormone-Stimulated Adrenocorticotropin and Cortisol before and after Weight Loss. Journal of Clinical Endocrinology & Metabolism, 82(6), 1874-1878. doi:10.1210/jc.82.6.1874

[27] Breen, K. M., & Karsch, F. J. (2004). Does Cortisol Inhibit Pulsatile Luteinizing Hormone Secretion at the Hypothalamic or Pituitary Level? Endocrinology, 145(2), 692-698. doi:10.1210/en.2003-1114

[28] Breen, K. M., & Karsch, F. J. (2004). Does Cortisol Inhibit Pulsatile Luteinizing Hormone Secretion at the Hypothalamic or Pituitary Level? Endocrinology, 145(2), 692-698. doi:10.1210/en.2003-1114

[29] Melcangi, R. C., Garcia-Segura, L. M., & Mensah-Nyagan, A. G. (2007). Neuroactive steroids: State of the art and new perspectives. Cellular and Molecular Life Sciences, 65(5), 777-797. doi:10.1007/s00018-007-7403-5

[30] Melcangi, R. C., Garcia-Segura, L. M., & Mensah-Nyagan, A. G. (2007). Neuroactive steroids: State of the art and new perspectives. Cellular and Molecular Life Sciences, 65(5), 777-797. doi:10.1007/s00018-007-7403-5

[31] Cappelletti, M., & Wallen, K. (2016). Increasing women's sexual desire: The comparative effectiveness of estrogens and androgens. Hormones and Behavior, 78, 178-193. doi:10.1016/j.yhbeh.2015.11.003


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