Is Intermittent Fasting Helpful for Women during Perimenopause?

Most of the research on intermittent fasting has been done on men and very little data exists on women, so I asked the question: is intermittent fasting helpful for women during perimenopause? This blog reviews the research on the impact of intermittent fasting on women’s health, weight and athletic performance during perimenopause.

smiling woman in shallow focus photography

What are Gender Differences in Exercise Physiology?

The unique training response of women throughout their menstrual cycle and into peri and post-menopause has been highlighted by the work of Dr Stacy Sims. The International Olympic Committee Consensus Statement on Relative Energy Deficiency in Sports (REDS) has highlighted the gender differences in the carbohydrate needs of athletes and how this predisposes all female athletes to the development of REDS. While we suspect that women may respond differently to fasting compared to men, there are many aspects to answer the question “Is Intermittent Fasting Helpful for Women during Perimenopause? This article reviews the science on the impact of intermittent fasting on women:

  1. Weight loss and body composition
  2. Exercise performance
  3. Health risks and insulin resistance

Time Restricted Eating in Scientific Studies

Intermittent Fasting is a broad term that includes one meal a day fasting, alternate day fasting, time restricted eating, as well as religious fasts, such as Ramadan. This article is a scientific review of alternate day fasting and Time Restricted Eating (TRE), which includes 16:8 or 20:4, where a person eats from during a 4 – 8 hour window. This summary does not address fasting from dawn to dusk for Ramadan, which has different health effects altogether. While alternate day fasting and TRE are technically subtypes of intermittent fasting, they are the main focus of this article and the research summarized below.

Intermittent Fasting Helps Weight Loss

Intermittent fasting helps women to lose weight.

There is strong research to show that intermittent fasting, more specifically TRE 16:8 is an effective way to achieve weight loss and specifically fat loss in women, at any age. However, intermittent fasting only helps you to lose weight by making it easier to eat less.  The amount of weight loss achieved with intermittent fasting is proportional to the amount of daily calories consumed.

Intermittent fasting works by reducing your Calorie intake.

A randomized control trial proved that intermittent fasting is not as effective as following a calorie restricted diet to lose weight [Templeman et al, 2021]. This study compared three diets for three weeks: a calorie restricted diet, an alternate day fast with caloric restriction, and an alternate day fast without caloric restriction. The calorie restricted diet resulted in more weight loss than both groups of intermittent fasting. Interestingly, the alternate day fasting group without caloric restriction, did not lose any weight.

Intermittent fasting is not as effective as cutting Calories.

Fortunately, a recent scientific review found that adults do not lose muscle while intermittent fasting, especially if they also do strength training. Most studies show that muscle mass is unchanged after
intermittent fasting.

Intermittent fasting does not impact your muscle mass.

The weight loss that is achieved with intermittent fasting tends to be body fat, specifically the deep fat in our tummy area. In fact, one study on a group of post menopausal women lost body fat and maintained their muscle after just 6 weeks of TRE from 12 pm-8 pm. Another study found that TRE between 7 am-3 pm was even more effective at fat loss, than TRE from 12pm-8pm.

Is Intermittent Fasting Effective for Active Women?

Unfortunately, there are no studies on intermittent fasting in active, peri or post-menopausal women. We do have some studies on active 20- to 30-year-old women. One such study found that 27yo active
women who did intermittent fasting combined with HIIT classes reduced abdominal fat after 8 weeks.

Intermittent fasting in active young women reduces waist size, too. Most of the studies on intermittent fasting and women were done on obese and inactive women, so we don’t yet know the impact of TRE on healthy, active middle-aged women. There are no studies on intermittent fasting in active or athletic middle-aged women.

 

How Does Intermittent Fasting Impact Women’s Health?

Almost all the research on intermittent fasting on health outcomes like insulin resistance, cholesterol, and autophagy has been done on obese, inactive men. Only one study [Heilbronn et al, 2012] to date has looked at the effect of intermittent fasting on insulin resistance in healthy, nonobese women aged 20-55 years old. Unlike the men, 3 weeks of intermittent fasting had a negative impact on insulin resistance in healthy, pre and perimenopausal women. However, this study used alternate day 24-hour
fasts for 3 weeks, which is quite different from the usual TRE 16:8. We still don’t know what impact TRE 16:8 may have on insulin resistance in healthy women. Yet this study was able to conclude an important gender difference: men have favorable effects, while women have unfavorable effects on insulin resistance after alternate-day fasting.

Fasting may have an unfavorable impact on insulin resistance, in healthy, non-obese, perimenopausal women.

Why do Perimenopausal Women respond to Intermittent Fasting differently?

As Dr Stacy Sims points out, women going through perimenopause shift to using more fat instead of glucose for energy, which may contribute to developing insulin resistance. Intermittent fasting for 12-16hours forces the body to rely more on fats than carbohydrates for energy. It makes sense that fasting may exasperate this effect in perimenopausal women.

Does Fasting Impact the Athletic Performance of Women?

A Systematic Review of 92 studies on intermittent fasting on sports performance, which was almost exclusively done on men, found that TRE improves power, aerobic performance, insulin sensitivity, and
body fat in men.

Intermittent fasting improves performance and health in men. One study stumbled upon an important gender difference on intermittent fasting. They measured the athletic performance of 20 collegial male and female athletes after an overnight fast or after breakfast. This study found that the fasted workouts seemed to give men an advantage and women a disadvantage on the bike!

Female athletes perform better in workouts after having breakfast. Regardless of gender, fatigue occurs when the body’s fuel stores of carbohydrates run low, reducing speed, reaction time, and muscle strength. Every athlete has experienced this feeling of hitting the wall when your legs turn to noodles and the workout feels so much harder. This is 100% a fueling issue.

As a general rule, athletes need to have a high carb meal 1-2 hours before endurance activity. For more information on how to optimize carbohydrates to fuel performance, read my blog on Everything Athletes Need to Know About Carbs.

What are the Risks of Intermittent Fasting for Perimenopausal Women?

Researchers have yet to test IF on perimenopausal women who engage in athletic training beyond a HIIT class.  However, many mature women are training and competing in endurance running, cycling, triathlons, racquet sports and paddling sports.

Intermittent Fasting has never been tested on athletic mature women.
Although women tend to eat far less than male athletes, our carbohydrate needs are much higher than male athletes. The 2023 IOC consensus statement on Relative Energy Deficiency in Sports (REDS) states that female athletes are at particularly high risk of developing REDs, a dangerous chronic condition that develops from low energy and carbohydrate intake. Female athletes experience symptoms of REDs when they consume less than 30Cal/kg fat-free mass per day, compared to male athletes who do not develop this problem until their intake drops below 10-25Cal/kg fat-free mass per day.

Female athletes need to consume more energy by body weight compared
to men, to avoid symptoms of low energy availability and REDs.

When athletic women compete in endurance sports, they need to ensure they meet their energy needs to avoid the health complications of REDs. Finally, we need to recognize the connection between intermittent fasting and restrictive eating disorder behaviors.

So, Is Intermittent Fasting Helpful for Women During Perimenopause?

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