There is a good chance you have heard about intermittent fasting (IF), as the popular diet has created quite the buzz over the last several years. According to a recent study done by HealthReporter, 24% of Americans confirmed they tried this method of eating in 2020, making it the most prevalent diet in the US that year. (1)
And for good reason, several studies have highlighted an array of positive health effects associated with IF, from weight loss and improved metabolic health to lower blood pressure and cholesterol levels. (2) A growing number of people have described experiencing these benefits for themselves, and even celebrities like Kourtney Kardashian and former Twitter CEO Jack Dorsey are weighing in on how IF has helped improve their health. In addition to all the reported health benefits, the big draw to IF is its convenience factor. Unlike most other dietary plans, IF is less restrictive about what you eat and more focused on when you eat it. This is appealing to many people as it gives you the freedom to eat what you want without limiting your intake of certain types of foods. Without having to go through a major pantry overhaul or dropping a fortune on food, you can start IF at any time with what you have in your kitchen right now.
But is this diet right for everyone? As is the case for most diets, the answer is no. Nutrition is highly individualized and what works for someone else may not work as well for you, or vice versa. When it comes to IF, emerging scientific evidence suggests that women may be one demographic that should proceed with caution. Data indicates that, compared to men, women may respond differently to a diet involving fasting or severe caloric restriction. Here’s what you might want to consider if you are thinking about trying out IF for yourself.
Hormonal Changes and Your Diet
While there is still limited research regarding IF, especially when considering its widespread popularity, the developing data regarding the relationship between hormones and fasting indicate some red flags for women. A 2022 study led by Krista Varady at the University of Illinois, Chicago found that women who were on an IF diet for 8 weeks experienced a 14% reduction in a hormone called DHEA.(3) This hormone is important for promoting healthy ovarian function and egg quality, something that women who are interested in getting pregnant likely want to optimize.
And while this data is an important piece of the puzzle, it is also important to note that these women were implementing a so-called “warrior diet,” where research participants were allowed a mere four-hour window to consume calories. If you’re thinking that seems like a pretty short time frame to ingest a day’s worth of nutrients, you would be right. This IF technique, when compared to the commonly used 16:8 or 14:10 methods, where you have eight and ten hours to eat respectively, is severe. As Varady reported to UIC Today, there doesn’t seem to be anything significant or special about timing when it comes to the IF diet. “All it’s doing is making people eat less,” she states. “By shortening that eating window you’re just naturally cutting calories.” (4)
Another study published in Nutrients found that IF could potentially cause a drop in testosterone in both women and men, contributing to negative health effects such as decreased metabolic health, muscle mass synthesis, and libido. (3) It’s not all bad news though, while these drops in testosterone were observed throughout the course of the study, none of the subjects reported any symptoms or negative side effects, indicating that perhaps long-term vs. short-term IF matters. That said, research is limited at this point and more data is needed.
Insulin and Blood Sugar Fluctuations
An increase in insulin sensitivity and improved blood sugar levels are often touted as one health benefit spurred by IF. However, this may not always be the case. One recent study found that insulin sensitivity was actually adversely affected when female subjects engaged in IF. It is still unclear as to why this may be but is something to be cautious of, nonetheless. Again, the research is somewhat murky at this point and more long-term data is needed. (5)
Major blood sugar fluctuations throughout the day can also accompany severely restrictive IF diets. Without regular meals, your blood sugar tends to dip drastically during a fasting period before spiking during and directly after your meals. This constant up and down, rather than a steady flow of glucose availability and thus energy, can cause reduced energy stores in your body. This often leads to increased hunger and fatigue throughout the day. (2)
The Fine Line Between Fasting and Depriving Your Body of Nutrients
The most important takeaway from the current IF data and research thus far is that we still don’t know much. This means that if you are going to try IF, knowing your body and how to fast safely is of the utmost importance. Starting with a more manageable fasting schedule like 16:8 or 14:10 (as mentioned above) is more feasible. With a more lenient IF plan, you will generally be getting enough calories and nutrients to sustain your energy needs and physiological functions throughout the day. IF schedules like the “warrior diet” or 5:2, where you eat normally for 5 days of the week and fast for two full days, can be difficult to manage at best. At worst, you could be wreaking havoc on your body and your hormone levels.
Some women should not consider IF as a viable diet option, as the cost far outweighs any potential benefits. If you know you have a history of an eating disorder or disordered eating, have preexisting health conditions (i.e., thyroid, adrenal, or autoimmune diseases), or are pregnant or trying to get pregnant, your best bet is to focus on eating nutritious, whole foods and not worry about fasting.
Science has yet to settle on a definitive answer concerning the long-term effects of intermittent fasting for women. Those who practice it describe various positive results, but those results remain anecdotal until they are backed up in clinical studies. If you care about your diet and want to make sure that you're doing everything you can to give yourself the best chance at a healthy life, then you might want to think twice before choosing to follow an intermittent fasting regimen. As with all diet plans, it’s a good idea to talk to your doctor or a dietician about any drastic changes you intend to make before you jump in feet first.
1. 34 intermittent fasting statistics and facts, HealthReporter, 2022. 34 Intermittent Fasting Statistics and Facts | HealthReporter Accessed 23 February 2023.
2. Food for thought—September, DrexelNews, 2022. Food for Thought: Intermittent Fasting: Pros, Cons and Why It’s Not for Everyone (drexel.edu) Accessed 23 February 2023.
3. Effects of intermittent fasting on reproductive hormone levels in females and males: A review of human trials, Nutrients, 2022. Effect of Intermittent Fasting on Reproductive Hormone Levels in Females and Males: A Review of Human Trials - PMC (nih.gov) Accessed 27 February 2023.
4. New data on how intermittent fasting affects female hormones, UIC Today, 2022. New data on how intermittent fasting affects female hormones | UIC Today Accessed 14 February 2023.
5. Glucose tolerance and skeletal muscle gene expression in response to alternate day fasting, Obesity Society, 2012. Glucose Tolerance and Skeletal Muscle Gene Expression in Response to Alternate Day Fasting - Heilbronn - 2005 - Obesity Research - Wiley Online Library Accessed 27 February 2023.
