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- Intermittent fasting may be less effective in women and could disrupt their menstrual cycle.
- However, intermittent fasting may still be beneficial for weight loss and reducing inflammation.
- The best intermittent fasting schedule for women is the 16:8 or 14:10 schedule.
- Visit Insider's Health Reference library for more advice.
Intermittent fasting is a popular, albeit, a different approach to weight loss because it focuses on when you eat instead of what you eat.
In addition to helping people lose weight, numerous studies suggest that intermittent fasting is a promising strategy to protect against cancer, diabetes, and cardiovascular diseases.
But, like every diet, intermittent fasting works differently for everyone. In particular, a handful of studies have found that it affects female participants differently compared to male participants.
Intermittent fasting may be less beneficial for women
Some research suggests intermittent fasting may be less effective for women – but it's worth noting existing studies are small and larger studies are needed to confirm results.
For example, in a 2005 study of eight men and eight women, researchers analyzed the effects of intermittent fasting on insulin sensitivity and glucose response. After three weeks, men saw an improvement in insulin sensitivity while their glucose response remained unchanged. Meanwhile, women saw no change in insulin sensitivity, and their glucose tolerance actually declined. Therefore, fasting may be less effective in women for weight loss and blood sugar management than men.
Intermittent fasting may also affect a woman's menstrual cycle.
That's because fasting for long periods can affect the hypothalamus or the part of the brain that regulates hormones like estrogen that are crucial to menstruation.
Intermittent fasting may also affect a woman's menstrual cycle, as the female reproductive system is sensitive to calorie restriction.
That's because fasting for long periods can affect the hypothalamus or the part of the brain that regulates hormones like estrogen that are crucial to menstruation.
So far, research has found that restricting calories, in general, can also lead to lower progesterone levels, which reduces the chances of ovulation.
That's why, "women who practice intermittent fasting should ensure they have a balanced diet with enough energy to support their needs," Andres Ayesta, RDN, founder of Planos Nutrition.
However, intermittent fasting may actually boost fertility for women with polycystic ovary syndrome.
In a small 2002 study, researchers found that obese women with PCOS who restricted their calories to 1,000 per day for one week, saw increased levels of the luteinizing hormone, which regulates ovulation.
To play it safe, women should try a fasting window no longer than 12 to 14 hours, says Samantha McKinney, registered dietitian and certified personal trainer at Life Time.
Important: If you're trying to conceive, consult with your doctor before trying intermittent fasting.
While evidence on how intermittent fasting affects women is still emerging, there seem to be some general benefits, like:
1. Weight loss
Intermittent fasting helps with weight loss by decreasing the amount of insulin in the body, a hormone that stores fat, says McKinney.
In a 2017 review of 16 studies, 11 found statistically significant weight loss as a result of intermittent fasting. In another 2014 review, participants experienced 3% to 8% weight loss over three to 24 weeks and a 4% to 7% reduction in waist circumference over six to 24 weeks.
Meanwhile, a small 2012 study of obese postmenopausal women found those who restricted calories through intermittent fasting for five weeks saw significant decreases in body weight, waist circumference, and fat percentage compared to those who just reduced calorie intake.
However, other studies say it's no different than just cutting back on calories.
2. Controls blood sugar
"Type 2 diabetes and other metabolic conditions, like prediabetes and insulin resistance, are characterized by blood-sugar imbalance and chronically high insulin," says McKinney. "Intermittent fasting may improve one's sensitivity to insulin, therefore supporting healthy blood sugar levels."
A 2014 review backs this up as it found eight to 12 weeks of intermittent fasting resulted in a 3% to 6% reduction in blood sugar levels and a 20% to 31% reduction in insulin in people with prediabetes.
3. Reduced inflammation
Chronic inflammation has been linked to health conditions such as cancer, heart disease, Alzheimer's, asthma, and type 2 diabetes.
A 2018 review found intermittent fasting can help fight inflammation by decreasing the level of certain inflammatory cytokines, which are small proteins secreted from immune cells that can cause inflammation and pain.
Another small 2019 study found fasting can reduce inflammation and improve chronic inflammatory diseases.
How to intermittent fast
Whether you're a man or woman, there are several different ways to try intermittent fasting. Here are some of the most popular ones:
16:8 fasting (or 14:10): Fast for 16 or 14 hours each day, and then eat within an eight or 10-hour window. For example, this may mean you stop eating at 7 PM and start eating at 11 AM the next day. This is the most popular form of intermittent fasting as you are asleep for the majority of the fast, making it more sustainable, says Ayesta and McKinney.
Alternate-day fasting: This is when you alternate days of regular eating with days of fasting or having just one meal with less than 500 calories. While this is one of the most well-researched strategies for weight loss and metabolic health, Ayesta says it can be too restrictive for some women and requires supervision from a dietitian or nutritionist.
5:2 fasting: This version has you fast for two consecutive days a week, and eat normal meals the other five days. Due to its extreme nature, Ayesta says it should only be adopted under the supervision of a health professional.
One meal a day: Here, you only eat one large meal daily, typically in the evening. However, this method can lead to binging episodes, says Ayesta, and should be implemented with caution - especially for those who are physically active.
Choosing the right method of intermittent fasting will depend largely on your personal goals and lifestyle. However, McKinney advises that women try the 14:10 method as it's less rigid, relatively simple to implement, and still offers enough time between meals to trigger healthy changes.
Insider's takeaway
Intermittent fasting may be helpful for women seeking to lose weight and control inflammation, but some small, preliminary research suggests that it could adversely affect blood sugar levels and fertility.
There are many different types of intermittent fasting, each suited to different preferences and lifestyles, but the 14:10 method is the easiest to implement and sustain for many women.
Check with your doctor before embarking on an intermittent fasting diet, especially if you have a pre-existing condition.