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After I finished breastfeeding, I began to engage in what I consider to be 16:8 intermittent fasting (IF) - I eat for an 8 hour window and fast for the other 16 hours. I mostly use IF as a tool to avoid unnecessary calorie intake (I personally tend to eat because of boredom or emotions in the evenings) and to give my digestive system a rest every day.
It turns out there is a lot more to IF, especially for women.
I know a lot of people who rave about the benefits of intermittent fasting that go beyond calorie control, so I decided to do some more research on the topic. I did find many evidence-based benefits of intermittent fasting such as:
Weight loss
Insulin resistance
Inflammation
Heart health
Cancer prevention
Brain health
Anti-aging
However, many of these studies have been conducted on animals and some studies show that intermittent fasting might affect women differently, and more adversely, than men.
Not knowing what to think of this, I checked in with Miami-based dietitian Lucette Talamas, MS, RD, LDN to help me navigate whether intermittent fasting is a good idea for women.
What is intermittent fasting?
Jacqui: What is intermittent fasting? Is there anything to it beyond restricting eating for a number of hours a day?
Lucette: Intermittent fasting (IF) is based on periodic restriction of food, shifting between periods of reduced/no energy intake and periods of unrestricted feeding.
While diets usually dictate what to eat, Intermittent Fasting (IF) is an eating regimen focusing on when to eat. The most common IF regimens are:
Daily time-restricted: restricting food (i.e. fasting) for 12-16 hours. Someone may refer to their time restriction as “16:8” which is a 16 hour fasting window and a 8 hour eating window.
The 16:8 method is a popular regimen where there is 16 hours of fasting, and 8 hours of feasting. Some recommend to start with a 12 hour window, and slowly increase to the 16 hours.
Alternate Day Modified Fasting: alternating days of usual eating with restricted eating (of about 500 calories per day).
The 5:2 intermittent fasting regimen is a popular method where one follows their notmral eating pattern 5 days a week, and then restricts eating to about 500 calories for 2 days.
The theory behind intermittent fasting is understanding that when the body enters fasting mode, there is a physiologic response that seems to positively effect on many areas. A metabolic ‘switch’ occurs 12-36 hours from the last ingestion of calories. During this metabolic ‘switch’, the body uses ketones instead of glucose for energy while also triggering a cascade of other metabolic cellular changes that may impact mental and physical performance as well as prevent certain chronic diseases. This switch can promote improved glucose metabolism, decreased inflammation, decreased blood pressure, improved heart health, and increased resistance of cells to stress and disease in humans. Some new studies in males have found potential benefits of IF on body composition when paired with resistance training. However, it is important to note that most research is done in animals (mice), compared to human studies. The concerns of animal studies is that they are not generalizable to humans. The studies we have on humans mostly focused on Ramadan fasting practices or use small sample sizes with specific populations (so not generalizable to all populations).
Source:
Anton SD, Moehl K, Donahoo WT, et al. Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting. Obesity (Silver Spring). 2018;26(2):254-268. doi:10.1002/oby.22065
Cabo, Rafael De, and Mark P. Mattson. “Effects of Intermittent Fasting on Health, Aging, and Disease.” New England Journal of Medicine 381, no. 26 (2019): 2541–51. doi.org/10.1056/nejmra1905136.
Health Benefits of Intermittent Fasting
Jacqui: I usually use intermittent fasting (16:8) for calorie restriction, but I’ve read that there are a lot of other health benefits. What do you think?
Lucette: These are 2 separate topics/interventions – intermittent fasting 16:8 regimen and calorie restriction. When two interventions are done at the same time, it is not possible to distinguish if the results are attributed to the IF metabolic ‘switch’ or caloric restriction. This is actually one of the caveats of current research of intermittent fasting with calorie restriction. Furthermore, if someone is losing weight while trying IF, we don’t really know if the health benefits seen could be due to the fasting or the actual weight loss. More research is needed in this area.
Interestingly, the idea of intermittent fasting is not as a means to restrict calories, as research does look into the metabolic effects and health benefits of IF without calorie restriction. Therefore, during the ‘feeding’ window, one can be eating their normally allotted daily calorie needs and theoretically still experience the presumed health benefits due to the fasting periods.
Intermittent Fasting for Women
Jacqui: I’ve also read that the research on these health benefits hasn’t really been done on women. What do you think of intermittent fasting for women specifically?
Lucette: As mentioned, since there is limited research in humans (compared to animals), more so less specific to populations like women of certain ages.
First of all, women who are pregnant or breastfeeding should not try intermittent fasting. In addition, it would not be recommended for women (or men) with medical conditions related to blood sugars, such as diabetes or hypoglycemia, to try this. It would also not be advisable for women with a history of an eating disorder to follow IF.
(see more below in #4)
Intermittent fasting while breastfeeding
Jacqui: Is it dangerous (or okay?) to partake in intermittent fasting while breastfeeding? What about while menstruating?
Lucette: It can be particularly concerning for women who are breastfeeding to follow IF. The woman’s body undergoes so many unique change postpartum while at the same time, faces an increased calorie demand to produce breastmilk (about 400-500 calories extra per day!). We don’t really know at this time what can happen to a woman’s milk supply during extended fasting such as in IF (~16 hour fasts). In addition, such regimented routines like IF can be stressful to follow, which there is no need to increase a new mom’s stress. Stress, fatigue, and calorie restriction can decrease milk production. In theory, breastfeeding alone should aid in postpartum weight loss, but there are other factors that also impact weight loss efforts including diet, physical activity, and amount of weight gained during pregnancy.
For women of childbearing age, any diet that promotes restriction can be concerning for certain women, especially those with a history of an eating disorder, disordered eating, or orthorexia. In order to have a menstrual cycle, the body needs to have a certain amount of calories to function properly. Calories are food energy that fuel our health systems- our respiratory, neurological, cardiac, reproductive, digestive systems to name a few. Food calories are found in macronutrients (carbs, fats, protein), along with micronutrients (vitamin and minerals) to keep our body healthy and functioning. Therefore, during IF, women should be eating enough calories and nutrient-rich foods during their ‘feeding’ windows to support a healthy body. Restricting calories too much over a period of time can negatively affect menstruation and even cause it to stop. In addition, there can also be a psychological impact from the extended food restriction time to enter fasting mode. Ultimately, it is not worth sacrificing a women’s health and her healthy relationship with food to try a new diet regimen.
Is intermittent fasting safe for moms
Jacqui: Do you think intermittent fasting is a safe tool for post-baby weight loss after a mother has finished breastfeeding?
Lucette: It could be, but I want to remind women that IF is not for everyone. Extended fasting is not easy for everyone to follow due to each person having a unique ‘metabolic switch’. IF can also have psychological impacts as the diet consists of periods of fasting (restriction) and feeding. We do need more robust research in the area specifically to women’s lifecycle stages.
Concerns about intermittent fasting
Jacqui: Do you have any concerns about intermittent fasting?
Lucette: There is no one-size-fits all approach to eating. While IF seems to have promising benefits in animal studies, it is not yet generalizable for all to follow. My concerns are for those who are not following IF correctly or following it on and off (‘yo-yo’ dieting). Instead, I’d recommend to focus on finding a healthy eating pattern that lasts a lifetime is key. This looks different for each person, depending on their life stage, activity level, medical history, and food preferences vary. A healthy eating pattern is also flexible, and most importantly, includes mindful eating. Any diet, even IF, can impact your relationship with food. A healthy eating plan is flexible and does not cause guilt. If any ‘diet’ causes you to feel guilty, has you overly preoccupied, or has led to unhealthy eating habits such as overeating during times of ‘feeding’, it is best not to follow it.
Lucette’s Recommendation
Jacqui: If you think intermittent fasting is an okay practice, is there a specific outline that you prefer?
Lucette: Bringing the science to real-world practice, I do not think there will be a single diet regimen that will work for everyone, or all women. In regards to IF, there are many factors we reviewed as to why IF should be approached cautiously if someone is thinking of trying it. Instead, I think it’s all about finding a healthy eating pattern that is flexible lifelong.
To keep things practical, I like to advice with these takeaways. Before becoming this new ‘fad’, fasting has been around historically for religious reasons and more commonly with overnight fasting (i.e. sleeping!), which has its benefits. My common sense advice starts by encouraging to get the recommended amounts of sleep each night (7-9 hours for most adults) to support regular overnight fasting, avoiding to eat prior to bedtime (GERD recommendations are 3 hours), and avoiding late night eating which has been associated with increased risk of chronic diseases. Combining these recommendations, people can be “intermittently fasting” for ~12 hours without even knowing it by just following general lifestyle principles.