Intermittent Fasting: Why Women Should Fast Differently than Men
In both men and women, hypothalamic-pituitary-gonadal (HPG) axis — the cooperative functioning of three endocrine glands — is a controller
First, the hypothalamus releases gonadotropin releasing hormone (GnRH) – this tells the pituitary to release luteinizing hormone (LH) and follicle stimulating hormone (FSH).
LH and FSH then act on the gonads (a.k.a. testes or ovaries)
In women, this triggers the production of estrogen and progesterone – which they need to release a mature egg (ovulation) and to support a pregnancy
In men, this triggers the production of testosterone and sperm production (2)
The reason for this, and the problems as a result of fasting are believed to be due to kisspeptin, a protein-like molecule that neurons use to communicate with each other
Kisspeptin stimulates GnRH production in both sexes, and we know it’s sensitive to leptin, insulin, and ghrelin, which react to hunger and satiety.
Females mammals have more kisspeptin than males – more kisspeptin neurons may mean greater sensitivity to changes in energy balance
This may be one reason why fasting more readily causes women’s kisspeptin production to dip, tossing their GnRH off kilter (2)
Female Rat Study – Journal PLoS One (Public Library of Science)
Study included 10 male and 10 female normal-sized rats.
Half the rats ate whenever they wanted; the other half ate only every second day.
In between feeding times, their food was removed and they fasted – this went on for 12 weeks, which is the equivalent of about 10 years in a human life
By the end of the 12 weeks, the fasting female rats had lost 19% of their body weight, their blood glucose levels were lower, and their ovaries had shrunk
Overall, the experiment affected the female rats’ hormones much more significantly than the males
While kisspeptin production went down in both male and female fasting rats, in the females, LH absolutely plummeted, while estradiol, a hormone that inhibits GnRH in humans, skyrocketed to four times higher than the normal level
The appetite hormone leptin was six times lower than in a normally fed female rat.
It only took 10-15 days for the experiment to disrupt their reproductive cycle.
In other words, the female rats’ hormones – both reproduction – and appetite-regulating – were of whack (3)
2 Additional Studies
One study (JAMA Internal Medicine), a year-long, randomized clinical trial, found that fasting didn’t impact obese women any differently than obese men
Alternate day calories – in which subjects ate 500 calories every other day and ate normally on the other days – helped both male and female subjects lose around 6% of their body weight (4)
Another study (Obesity Research) from 2005 suggests that fasting could reduce women’s insulin sensitivity slightly more than men’s, causing their blood sugar to spike higher after a meal
Diminished insulin sensitivity also makes it harder to digest carbs and absorb nutrients, increasing the odds of gaining weight.
However, the study was short and small – it looked at eight women for just two weeks. Concluded that it wasn’t enough time to see how fasting really affects the body (5)
1) Intermittent Fasting For Women, What You Need To Know To Avoid Hormonal Imbalance. (2017, May 17). Retrieved from http://www.collective-evolution.com/2017/05/17/intermittent-fasting-for-women-what-you-need-to-know-to-avoid-hormonal-imbalance/
2) Intermittent Fasting for women: Important information you need to know. (2015, March 25). Retrieved from https://www.precisionnutrition.com/intermittent-fasting-women
3) Intermittent Fasting Dietary Restriction Regimen Negatively Influences Reproduction in Young Rats: A Study of Hypothalamo-Hypophysial-Gonadal Axis. (2013, January 29). Retrieved from http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0052416
4) Trepanowski JF , et al. (n.d.). Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults: A Randomized Cli… – PubMed – NCBI. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/28459931
5) Heilbronn LK , et al. (n.d.). Glucose tolerance and skeletal muscle gene expression in response to alternate day fasting. – PubMed – NCBI. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/15833943
6) Fasting and Thyroid. (n.d.). Retrieved from http://www.drsarasolomon.com/fasting-and-thyroid/