Women and Fasting: If you’ve been following my work, then you know that I’m a big proponent of both the keto diet and intermittent fasting for their impressive health benefits. More and more research continues to come out daily in support of these lifestyles. However, while some of these studies are centered on women, the majority of the studies examine men. Since men and women are so biologically different, can we extrapolate the same benefits to women? The short answer is yes. But based on what I’ve seen in practice, we often need to make a few adjustments. Let’s take a closer look to see how these diets may affect women differently than men and what modifications we can make to facilitate success.
Women and Fasting: Why are keto and fasting so beneficial for health?
As a quick reminder, intermittent fasting (IF) and keto are two diets that promote the body’s innate biological systems for positive health benefits. Both rely on the concept that small amounts of stress promote a positive adaptation in the body that can lead to weight loss, cognitive improvement, longevity, and more.
Intermittent fasting takes the benefits of extended fasting and packages them into a sustainable practice that can be continued long-term. Fasting is not a new concept and has been around for thousands of years in both religious traditions and for health benefits. When the body is in a fasting state, it can focus on repair and recovery as opposed to anabolism, or building as we see when nutrients are available. The body will always choose cellular growth when in a fed state, but fasting forces the body to pause. Essential biological functions like autophagy, the body’s way of removing cellular waste and debris, can only occur during fasting.
Similarly, ketogenic diets move the body out of a constant insulin-producing, inflammatory state (as can be seen in those who follow a more standard American diet) and into a fat-burning state of ketosis. As with fasting, the removal of certain nutrients (namely glucose) forces the body to adapt and adjust to using fat for the majority of energy, and gluconeogenesis for whatever is remaining. Autophagy can also occur during periods of ketosis.
Ketone bodies can be produced both in periods of fasting, as well as while following the ketogenic diet. They are not only used for fuel when glucose is no longer available but also act as signaling molecules to turn on genes such as brain-derived neurotrophic factor (BDNF). BDNF helps to stimulate new neurons in the brain as well as promote genes that support oxidative damage repair.
Both the keto diet and IF have impressive benefits, including:
- Weight loss
- Cardiovascular improvements
- Improved insulin sensitivity and blood sugar
- Brain and neurological health
- Immune health
However, as mentioned, more research needs to be conducted in female versus male subjects to see how reproductive hormones may affect these changes. Like any diet, results are individualized, and men may respond differently than women, as you will see below.
Women and Fasting: What does the research say about women and keto or fasting?
Because women’s hormones are so beautifully complex, studies done on men can’t always be translated to women’s health in the same way. Blood sugar, weight, nutrients, and sex hormones are all very interconnected. While it’s clear that many women can and will be successful with fasting and keto, some women may need to adjust the way they adopt these lifestyles to make it a healthy, long-term approach.
For example, in a study conducted on male and female mice following the keto diet, men continued to lose weight throughout the study. In contrast, female rats shifted to weight gain. High-fat diets can also increase women’s estrogen levels. This increase can have a downstream effect over time as estrogen in excess can not only suppress the thyroid but also lead to hormonal imbalances that make it difficult to lose weight.
Women’s hormones can also be sensitive to nutrient changes, especially as seen with fasting. A study on IF found women were more likely to experience impaired insulin responses after three weeks of fasting as compared to men. Over time, fasting can move from a positive stress adaptation to a negative one. The body can begin to feel the need to protect itself from what it perceives is a threat of undernutrition.
Reproductive hormones are not considered essential by the body during times of stress. They can even be temporarily downregulated or shut down completely, while stress hormones increase. This downregulation can lead to hormonal imbalances for women with disruptions in menstrual cycles, adrenal fatigue or energy imbalances, and weight gain – the very things you may be starting keto or IF to avoid.
Women and Fasting: How can women adjust keto and IF to work with their biology?
It’s essential to recognize that not all women will have these negative adaptations. Still, given the risk, it makes sense to follow a plan that prevents it from occurring in the first place. The best way to do this is to cycle between the diets, allowing days in between for more carbohydrates or eating in an unrestricted window. This variation enables the body to feel “safe.” The negative adaptations only occur when the body feels it is in danger – perhaps missing out on specific nutrients or when fasting for more extended periods. It will upregulate hormones to protect and conserve resources.
If periods of keto are cycled with days of increased carbs, the body can relax, and the stress hormones will reduce. Similarly, with fasting, instead of practicing IF every day, women may consider alternate days of fasting or fasting only a few days a week. You can see the exact same health benefits when following it this way, while again reducing the risk of the body moving into a protective stress mode.
If you’ve read any of my articles on diet variation, then you know this is a concept I teach for both men and women. There isn’t any research available on the long-term benefits of these diets yet. Still, based on years of work, I’ve seen the benefit of cycling and keeping the body on its toes. As an added benefit, diet variation also helps to avoid the dreaded weight loss plateaus that can also stem from hormonal adaptations that signal hunger to the brain. Plus, the more often you follow this pattern, the quicker you become at fat adaptation as you cycle between keto, fasting, and increased days of carbs.
If you are just getting started on your keto or fasting journey, it can seem counterintuitive to promote days of increased carbs, or larger windows of eating. But this process will not only make you more efficient at burning fat and moving into ketosis, but it will also keep you healthy long-term. Diets only work when they become sustainable lifestyle changes. Diet variation helps to make this a realistic concept, especially when it comes to supporting women’s health while following keto or IF.
1. Longo, Valter D, and Mark P Mattson. “Fasting: molecular mechanisms and clinical applications.” Cell metabolism vol. 19,2 (2014): 181-92. doi:10.1016/j.cmet.2013.12.008
2. De Cabo, R., & Mattson, M. P. (2019). Effects of Intermittent Fasting on Health, Aging, and Disease. New England Journal of Medicine, 381(26), 2541–2551. doi:10.1056/nejmra1905136
3. Chen, Xihang et al. “Autophagy in Stem Cell Biology: A Perspective on Stem Cell Self-Renewal and Differentiation.” Stem cells international vol. 2018 9131397. 21 Jan. 2018, doi:10.1155/2018/9131397
4. Hyde, Parker N et al. “Dietary carbohydrate restriction improves metabolic syndrome independent of weight loss.” JCI insight, vol. 4,12 e128308. 20 Jun. 2019, doi:10.1172/jci.insight.128308
5. Anton, Stephen D et al. “Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting.” Obesity (Silver Spring, Md.) vol. 26,2 (2018): 254-268. doi:10.1002/oby.22065
6. Puchalska, Patrycja, and Peter A Crawford. “Multi-dimensional Roles of Ketone Bodies in Fuel Metabolism, Signaling, and Therapeutics.” Cell metabolism vol. 25,2 (2017): 262-284. doi:10.1016/j.cmet.2016.12.022
7. Bueno NB, de Melo IS, de Oliveira SL, et al. Very-low-carbohydrate ketogenic diet v low-fat diet for long-term weight loss: a meta-analysis of randomized controlled trials. 2013. In: Database of Abstracts of Reviews of Effects (DARE): Quality-assessed Reviews [Internet]. York (UK): Centre for Reviews and Dissemination (UK); 1995-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK138038/
8. Hyde, Parker N et al. “Dietary carbohydrate restriction improves metabolic syndrome independent of weight loss.” JCI insight vol. 4,12 e128308. 20 Jun. 2019, doi:10.1172/jci.insight.128308
9. Fontana, Luigi et al. “Extending healthy life span–from yeast to humans.” Science (New York, N.Y.) vol. 328,5976 (2010): 321-6. doi:10.1126/science.1172539
10. de Cabo, Rafael, and Mark P Mattson. “Effects of Intermittent Fasting on Health, Aging, and Disease.” The New England journal of medicine vol. 381,26 (2019): 2541-2551. doi:10.1056/NEJMra1905136
11. Longo, Valter D, and Mark P Mattson. “Fasting: molecular mechanisms and clinical applications.” Cell metabolism vol. 19,2 (2014): 181-92. doi:10.1016/j.cmet.2013.12.008
12. Gano, Lindsey B et al. “Ketogenic diets, mitochondria, and neurological diseases.” Journal of lipid research vol. 55,11 (2014): 2211-28. doi:10.1194/jlr.R048975
13. Cheng, Chia-Wei et al. “Prolonged fasting reduces IGF-1/PKA to promote hematopoietic-stem-cell-based regeneration and reverse immunosuppression.” Cell stem cell vol. 14,6 (2014): 810-23. doi:10.1016/j.stem.2014.04.014
14. Comitato, Raffaella et al. “Sex hormones and macronutrient metabolism.” Critical reviews in food science and nutrition vol. 55,2 (2015): 227-41. doi:10.1080/10408398.2011.651177
15. Sex Differences in the Response of C57BL/6 Mice to Ketogenic Diets JESSE COCHRAN, PAUL V. TAUFALELE, KEVIN D. LIN, YUAN ZHANG, E. DALE ABEL Diabetes Jul 2018, 67 (Supplement 1) 1884-P; DOI: 10.2337/db18-1884-P
16. Santin, Ana Paula, and Tania Weber Furlanetto. “Role of estrogen in thyroid function and growth regulation.” Journal of thyroid research vol. 2011 (2011): 875125. doi:10.4061/2011/875125
17. Heilbronn, Leonie K et al. “Glucose tolerance and skeletal muscle gene expression in response to alternate day fasting.” Obesity research vol. 13,3 (2005): 574-81. doi:10.1038/oby.2005.61
18. Rooney, Kristin L, and Alice D Domar. “The relationship between stress and infertility.” Dialogues in clinical neuroscience vol. 20,1 (2018): 41-47.