Intermittent Fasting for Women of Reproductive Age

Benefits of Intermittent fasting

Intermittent fasting has grown in popularity over recent years and for good reason. Intermittent fasting boasts some pretty impressive health benefits. These aren’t just claims by people trying to push certain weight-loss diets to make money, the health benefits actually have some pretty significant scientific backing. We have multiple studies that show us that intermittent fasting can help with weight loss (1), improve insulin resistance and diabetes risk (1), promote detoxification and cellular repair, improve egg quality and decrease reproductive aging in the ovary (6), can reduce oxidative stress and inflammation in the body (4), helps improve brain health and reduces the risk of depression and developing Alzheimer’s disease (2) and even change gene expression and increase lifespan (3).

How Intermittent fasting affects women of reproductive age

For women, in particular, blood sugar balance, insulin resistance and inflammation are often the root causes of many hormonal imbalances associated with the menstrual cycle and infertility so intermittent fasting should be a powerful tool in helping correct some underlying problems and achieve overall hormonal balance. However, as many women of reproductive age (including myself) can attest, intermittent fasting can make hormone balance a lot worse, increase mood swings and irritability and lead to irregular menstrual cycles and even a loss of menstrual cycle over time. Although intermittent fasting can have some positive benefits for women short term, long-term intermittent fasting can be very stressful on the system. When I was in my fertility awareness training, we were presented with various menstrual cycle charts of women who had infertile cycles due to short luteal phase, delayed ovulation, long cycles and absent periods due to intermittent fasting. It is a real and observable thing and it’s also quite easy to observe how ovulation returns to normal once women start to eat breakfast!

So why does this happen when all the science says otherwise?

1. Most scientific studies in the nutrition and exercise space are conducted on men and women in menopause. For decades, scientists have considered the hormonal variations of the menstrual cycle in women to be difficult to account for in studies. Even when studies have been done on women, they have usually occurred only in the mid-follicular phase where women tend to have hormone levels more similar to men. Although there is evidence that intermittent fasting is beneficial for women in menopause, we simply do not have the research to make the same claim for women of childbearing age, and in fact, we know that severe calorie restriction and fasting can be dangerous in pregnancy and lactation (6).

2. Most intermittent fasting regimes that women undertake do not support the normal physiology of the human body or take into account daily and monthly rhythms like the circadian rhythm (daily clock) or infradian rhythm (female monthly clock: the menstrual cycle). The most popular intermittent fasting schedules promote skipping breakfast or having a late breakfast. The morning is the time when our bodies most effectively and efficiently use food as energy. We need adequate energy intake at the beginning of the day to help give us the energy for the activity of the day ahead. We need less energy at night when our bodies are prepping to go to sleep and conserve energy for the night of inactivity that occurs at sleep. For women our calorie needs and insulin sensitivity change throughout the month depending on which part of the cycle we are in, estrogen in particular makes us more insulin sensitive (8) (9) giving us an overall metabolic advantage over men and menopausal women. As estrogen fluctuates women can respond differently to intermittent fasting within one menstrual cycle alone (9).

3. We have one study showing that fasting affects the hypothalamus, pituitary thyroid axis (HPT axis) and can actually have the opposite effect of weight loss in women of reproductive age. Fasting can create a state of stress on the body which can directly affect the thyroid by down-regulating the thyroid response. This slows down metabolism and can actually lead to weight gain (7). Theories as to why this occurs have to do with the female body wanting to store fat as a survival mechanism in times of stress.

4. Intermittent fasting in most cases results in calorie restriction. Calorie restriction has been shown to be detrimental to the female reproductive system. Energy deficiency through restriction of calories or overexercising leads to luteal phase defects (short luteal phase and infertile cycle) or low serum progesterone levels in the luteal phase and delayed ovulation (5) if energy deficiency is extreme such as in women with eating disorders or in overexercise, then we observe suppression of GnRH hormone which directly shuts down ovulation leading to a loss of period and infertility (6).

How do we get all the benefits of intermittent fasting without sacrificing our fertility, menstrual cycle and steady moods?

1. Never skip breakfast. Eating breakfast is one of the best things to do for overall blood sugar balance. It sets the tone for the rest of the day. The body needs and wants energy in the morning to replenish used glycogen stores from the night of fasting, it also needs the energy to help prepare it for the activity of the day.

2. Do not snack throughout the day. This is the gentlest form of intermittent fasting. Digestion requires a good 5-6 hours to process food after it is ingested. Eating well-balanced calorie sufficient meals that are spaced out by large breaks in between meals helps the digestion to work efficiently and digestive hormones adequate time to work and detox waste as well.

3. Keep the evening meal lighter and well before bedtime. In the evening our body starts switching to conservation mode to conserve energy for the long night of sleep with no food. Eating in the evening can actually have double the effect on blood sugar as eating earlier in the day, can lead to weight gain. Evening/night is also the time when digestion is controlled by the parasympathetic nervous system and is therefore in a state of “rest and digest.” Eating during this time arouses our digestive organs to work when they should be resting, therefore digestion is slowed and compromised which leads to poorer detoxification capacity (hello estrogen dominance, difficulty sleeping, PMS and constipation). Skipping the evening meal is a much safer choice for intermittent fasting than skipping breakfast as it works with the body’s natural clock (as long as caloric intake is still sufficient).

4. Eat enough food and don’t restrict calories. Our reproductive years are years of high energy expenditure. The ovary itself requires a lot of energy to do its job (the ovary has one of the highest concentrations of mitochondria -energy-producing organelles in the cell – in the entire body). Pregnancy and breastfeeding are also hugely energy demanding. Intermittent fasting would be a lot safer for women if it didn’t lead to overall calorie restriction. Sufficient calories daily (not too much not too little) are necessary for the proper functioning of our hormonal systems. Women that do well with intermittent fasting are the ones who still manage to eat sufficient calories outside of their fasting window.

5. Keep fasting to nighttime and do not exceed a fasting window greater than 12-14 hours at max. Keeping the fast to nighttime works with the body’s natural clock. Most of the liver’s glycogen stores are depleted at night when we sleep, hence why it is important to eat breakfast to replenish stores early in the morning. Women generally do better with shorter fasting windows than men. While men can go p to 18 hours, 14 hours is considered the maximum for women by many health professionals.

6. Eat according to your menstrual cycle phases. We need an average of 300 calories more in the menstrual and luteal phases than we do in the follicular and ovulatory phases. Similarly, we are more insulin sensitive in the follicular and ovulatory phase and more insulin resistant in the luteal phase. Many women feel better when they practice intermittent fasting in the follicular phase only. It is generally unadvised to try fasting for longer than 12-13 hours overnight in the luteal phase.

All of these tips are explained further in my blood sugar article which you can find here

Who should not do intermittent fasting at all?

Some women are more sensitive to intermittent fasting than others. In general people with anxiety or trauma should not try fasting. Under a state of heightened stress, the glycogen in the liver is depleted more quickly which can lead to blood sugar drops that further trigger more stress. Women with adrenal and thyroid problems are also advised not to fast for prolonged periods of time as the added stress of fasting can worsen the condition. Pregnant and breastfeeding women should not fast and eat as needed and required to support additional energy needs. There are many other medical conditions that may make fasting an unsafe choice, so it’s best to seek advice from a professional if needed and as always keep fasting gentle and mostly confined to the nighttime.