Intermittent fasting has become increasingly popular in recent years.
Unlike most diets that tell you what to eat, intermittent fasting focuses on when to eat by incorporating regular short-term fasts into your routine.
This way of eating may help you consume fewer calories, lose weight and lower your risk of diabetes and heart disease.
However, a number of studies have suggested that intermittent fasting may not be as beneficial for women as it is for men. For this reason, women may need to follow a modified approach.
Here is a detailed beginner’s guide to intermittent fasting for women.
Intermittent fasting (IF) describes a pattern of eating that cycles between periods of fasting and normal eating.
The most common methods include fasting on alternate days, daily 16-hour fasts or fasting for 24 hours, two days a week. For the purpose of this article, the term intermittent fasting will be used to describe all regimens.
Unlike most diets, intermittent fasting does not involve tracking calories or macronutrients. In fact, there are no requirements about what foods to eat or avoid, making it more of a lifestyle than a diet.
Many people use intermittent fasting to lose weight as it is a simple, convenient and effective way to eat less and reduce body fat (1, 2).
It may also help reduce the risk of heart disease and diabetes, preserve muscle mass and improve psychological well-being (2, 3, 4).
What’s more, this dietary pattern can help save time in the kitchen as you have fewer meals to plan, prepare and cook (5).
There is some evidence that intermittent fasting may not be as beneficial for some women as it is for men.
One study showed that blood sugar control actually worsened in women after three weeks of intermittent fasting, which was not the case in men (6).
There are also many anecdotal stories of women who have experienced changes to their menstrual cycles after starting intermittent fasting.
Such shifts occur because female bodies are extremely sensitive to calorie restriction.
When calorie intake is low — such as from fasting for too long or too frequently — a small part of the brain called the hypothalamus is affected.
This can disrupt the secretion of gonadotropin-releasing hormone (GnRH), a hormone that helps release two reproductive hormones: luteinizing hormone (LH) and follicle stimulating hormone (FSH) (7, 8).
When these hormones cannot communicate with the ovaries, you run the risk of irregular periods, infertility, poor bone health and other health effects (7).
Although there are no comparable human studies, tests in rats have shown that 3–6 months of alternate-day fasting caused a reduction in ovary size and irregular reproductive cycles in female rats (9, 10).
For these reasons, women should consider a modified approach to intermittent fasting, such as shorter fasting periods and fewer fasting days.
Intermittent fasting not only benefits your waistline but may also lower your risk of developing a number of chronic diseases.
Heart disease is the leading cause of death worldwide (11).
High blood pressure, high LDL cholesterol and high triglyceride concentrations are some of the leading risk factors for the development of heart disease.
One study in 16 obese men and women showed intermittent fasting lowered blood pressure by 6% in just eight weeks (2).
The same study also found that intermittent fasting lowered LDL cholesterol by 25% and triglycerides by 32% (2).
However, the evidence for the link between intermittent fasting and improved LDL cholesterol and triglyceride levels is not consistent.
A study in 40 normal-weight people found that four weeks of intermittent fasting during the Islamic holiday of Ramadan did not result in a reduction in LDL cholesterol or triglycerides (12).
Higher-quality studies with more robust methods are needed before researchers can fully understand the effects of intermittent fasting on heart health.
Intermittent fasting may also effectively help manage and reduce your risk of developing diabetes.
Similar to continuous calorie restriction, intermittent fasting appears to reduce some of the risk factors for diabetes (3, 13, 14).
It does so mainly by lowering insulin levels and reducing insulin resistance (1, 15).
In a randomized controlled study of more than 100 overweight or obese women, six months of intermittent fasting reduced insulin levels by 29% and insulin resistance by 19%. Blood sugar levels remained the same (16).
What’s more, 8–12 weeks of intermittent fasting has been shown to lower insulin levels by 20–31% and blood sugar levels by 3–6% in individuals with pre-diabetes, a condition in which blood sugar levels are elevated but not high enough to diagnose diabetes (3).
However, intermittent fasting may not be as beneficial for women as it is for men in terms of blood sugar.
A small study found that blood sugar control worsened for women after 22 days of alternate-day fasting, while there was no adverse effect on blood sugar for men (6).
Despite this side effect, the reduction in insulin and insulin resistance would still likely reduce the risk of diabetes, particularly for individuals with pre-diabetes.
Intermittent fasting can be a simple and effective way to lose weight when done properly, as regular short-term fasts can help you consume fewer calories and shed pounds.
A number of studies suggest that intermittent fasting is as effective as traditional calorie-restricted diets for short-term weight loss (17, 18).
A 2018 review of studies in overweight adults found intermittent fasting led to an average weight loss of 15 lbs (6.8 kg) over the course of 3–12 months (18).
Another review showed intermittent fasting reduced body weight by 3–8% in overweight or obese adults over a period of 3–24 weeks. The review also found that participants reduced their waist circumference by 3–7% over the same period (3).
It should be noted that the long-term effects of intermittent fasting on weight loss for women remain to be seen.
In the short term, intermittent fasting seems to aid in weight loss. However, the amount you lose will likely depend on the number of calories you consume during non-fasting periods and how long you adhere to the lifestyle.
It May Help You Eat Less
Switching to intermittent fasting may naturally help you eat less.
One study found that young men ate 650 fewer calories per day when their food intake was restricted to a four-hour window (19).
Another study in 24 healthy men and women looked at the effects of a long, 36-hour fast on eating habits. Despite consuming extra calories on the post-fast day, participants dropped their total calorie balance by 1,900 calories, a significant reduction (20).
Other Health Benefits
A number of human and animal studies suggest that intermittent fasting may also yield other health benefits.
- Reduced inflammation: Some studies show that intermittent fasting can reduce key markers of inflammation. Chronic inflammation can lead to weight gain and various health problems (12, 21, 22).
- Improved psychological well-being: One study found that eight weeks of intermittent fasting decreased depression and binge eating behaviors while improving body image in obese adults (4).
- Increased longevity: Intermittent fasting has been shown to extend lifespan in rats and mice by 33–83%. The effects on longevity in humans is yet to be determined (23, 24).
- Preserve muscle mass: Intermittent fasting appears to be more effective at retaining muscle mass compared to continuous calorie restriction. Higher muscle mass helps you burn more calories, even at rest (25, 26).
Specifically, the health benefits of intermittent fasting for women need to be studied more extensively in well-designed human studies before any conclusions can be drawn (27).
When it comes to dieting, there is no one-size-fits-all approach. This also applies to intermittent fasting.
Generally speaking, women should take a more relaxed approach to fasting than men.
This may include shorter fasting periods, fewer fasting days and/or consuming a small number of calories on the fasting days.
Here are some of the best types of intermittent fasting for women:
- Crescendo Method: Fasting 12–16 hours for two to three days a week. Fasting days should be nonconsecutive and spaced evenly across the week (for example, Monday, Wednesday and Friday).
- Eat-stop-eat (also called the 24-hour protocol): A 24-hour full fast once or twice a week (maximum of two times a week for women). Start with 14–16 hour fasts and gradually build up.
- The 5:2 Diet (also called “The Fast Diet”): Restrict calories to 25% of your usual intake (about 500 calories) for two days a week and eat “normally” the other five days. Allow one day between fasting days.
- Modified Alternate-Day Fasting: Fasting every other day but eating “normally” on non-fasting days. You are allowed to consume 20–25% of your usual calorie intake (about 500 calories) on a fasting day.
- The 16/8 Method (also called the “Leangains method”): Fasting for 16 hours a day and eating all calories within an eight-hour window. Women are advised to start with 14-hour fasts and eventually build up to 16 hours.
Whichever you choose, it is still important to eat well during the non-fasting periods. If you eat a large amount of unhealthy, calorie-dense foods during the non-fasting periods, you may not experience the same weight loss and health benefits.
At the end of the day, the best approach is one that you can tolerate and sustain in the long-term, and which does not result in any negative health consequences.
Getting started is simple.
In fact, chances are you’ve already done many intermittent fasts before. Many people instinctively eat this way, skipping morning or evening meals.
The easiest way to get started is to choose one of the intermittent fasting methods above and give it a go.
However, you don’t need to necessarily follow a structured plan.
An alternative is to fast whenever it suits you. Skipping meals from time to time when you don’t feel hungry or don’t have time to cook can work for some people.
At the end of the day, it doesn’t matter which type of fast you choose. The most important thing is to find a method that works best for you and your lifestyle.
Modified versions of intermittent fasting appear to be safe for most women.
That being said, a number of studies have reported some side effects including hunger, mood swings, lack of concentration, reduced energy, headaches and bad breath on fasting days (1, 18).
There are also some stories online of women who report that their menstrual cycle stopped while following an intermittent fasting diet.
If you have a medical condition, you should consult with your doctor before trying intermittent fasting.
Medical consultation is particularly important for women who:
- Have a history of eating disorders.
- Have diabetes or regularly experience low blood sugar levels.
- Are underweight, malnourished or have nutritional deficiencies.
- Are pregnant, breastfeeding or trying to conceive.
- Have fertility problems or a history of amenorrhea (missed periods).
At the end of the day, intermittent fasting appears to have a good safety profile. Yet, if you experience any problems — such loss of your menstrual cycle — stop immediately.
Intermittent fasting is a dietary pattern that involves regular, short-term fasts.
The best types for women include daily 14–16 hour fasts, the 5:2 diet or modified alternate-day fasting.
While intermittent fasting has been shown to be beneficial for heart health, diabetes and weight loss, some evidence indicates it may have negative effects on reproduction and blood sugar levels in some women.
That being said, modified versions of intermittent fasting appear safe for most women and maybe a more suitable option than longer or stricter fasts.
If you are a woman looking to lose weight or improve your health, intermittent fasting is definitely something to consider.