If you are familiar with the women’s health space, you will know that intermittent fasting is generally not advised for women of reproductive age. This is because the vast majority of research on intermittent fasting has been conducted on men or post-menopausal women. This means there is little knowledge on how intermittent fasting effects the physiology of a cycling woman. Anecdotally and in clinic, it is observed that intermittent fasting can cause some negative health consequences for women’s hormones and fertility, especially when engaged in long term. (You can read more about this in my articles on intermittent fasting here) However, many women wish to know how they can get all the benefits of intermittent fasting without the potential negative effects on women’s hormones and fertility. This is where time-restricted eating comes in. While both strategies involve time-restricted eating patterns, they differ in their specific methodologies and goals.
Intermittent Fasting vs. Time-Restricted Eating:
Intermittent fasting revolves around alternating cycles of fasting and eating. Common approaches include the 16/8 method, where individuals fast for 16 hours and consume their daily caloric intake within an 8-hour window, the most popular method involved skipping the morning meal. Another method is the 5:2 method, which involves eating normally for five days and significantly reducing calorie intake for the remaining two days. On the other hand, time-restricted eating narrows the eating window without necessarily affecting overall calorie intake. It emphasises consuming meals within a specific time frame earlier in the day and generally recommends an eating window of 10-12 hours. An example of time-restricted eating that is supportive of female physiology focuses on maintaining an overnight or evening fast, typically lasting 12 to 14 hours. This approach involves consuming breakfast within 1-2 hours of waking up, allowing 4-6 hours between meals throughout the day, and finishing the last meal at least 3 hours before bedtime. By adhering to these guidelines, women can ensure a sufficient overnight fasting period that promotes optimal metabolic function and supports the body’s natural circadian rhythms while also maintaining optimal blood sugar control.
The Benefits of Eating Breakfast:
Time-restricted eating emphasises the importance of eating breakfast. After a full nights sleep, the body has depleted its glucose stores. This means that blood sugar is low. When blood sugar gets low (and no food is ingested) the body increases cortisol production in order to break down muscle and create glucose that can move into the blood. This process is often inflammatory. A recent large study with over 70,000 participants in China found that habitually skipping breakfast lead to an increase in inflammatory markers in the body, most noticeably CRP. For women, the combination of calorie restriction, heightened adrenalin and inflammation in the mornings can interfere with the production of reproductive hormones (read my article on how hormones are affected by intermittent fasting here) Inflammation, calorie restriction and low nutrient intake can in turn also compromise liver and gut function, which contribute to symptoms of estrogen dominance (read my article on estrogen dominance here).
Avoiding Late-Night Eating:
Eating late at night can disrupt natural circadian rhythms and interfere with the quality of sleep. When food is consumed close to bed time, the body focuses on digestion instead of winding down for restful sleep. Additionally, late-night eating has been linked to weight gain and poor metabolic health. Eating late at night can have a significant impact on blood sugar control, as the body becomes increasingly more insulin resistant during this time. In the evening and during sleep, the body’s sensitivity to insulin decreases, making it harder for glucose to enter the cells efficiently. When food is consumed late at night, it can lead to elevated blood sugar levels and a greater demand for insulin production than at other times of the day. This can strain the pancreas and potentially contribute to long-term insulin resistance, weight gain, and the development of conditions like type 2 diabetes. To support healthy sleep patterns and metabolic function, it is advisable to finish the last meal of the day at least 3 hours prior to bedtime. This practice allows ample time for digestion and promotes a more restful night’s sleep.
Time-Restricted Eating Guidelines:
Emphasising the Overnight Fast:
The overnight fast is a critical component of time-restricted eating. By extending the fasting period in the evening as opposed to the morning, the body is allowed to restore, repair and detoxify hormones. During the fast, insulin levels decrease, and the body taps into stored energy reserves (glycogen), promoting fat burning and improved insulin sensitivity. This overnight fast, averaging 12 to 14 hours, offers numerous benefits, including weight management, improved blood sugar control, and enhanced cellular repair processes. This has been specifically noted on women with PCOS, which had better results with lowering testosterone and DHEA levels with an extended evening fast instead of a morning fast.
Aligning with Circadian Rhythms & Infradian Rhythms:
The body operates on a 24-hour internal clock known as the circadian rhythm. Aligning eating patterns with this rhythm can have a profound impact on overall health. Research suggests that consuming the majority of calories during the daylight hours, when the body is more insulin-sensitive and metabolically active, can enhance weight management, improve blood sugar control, and support hormonal balance. This is because the body becomes more insulin resistant at night. For reproductive aged women it is also crucial to tune into the second biological clock called the infradian rhythm. This rhythm is dictated by the menstrual cycle. Calorie needs and insulin sensitivity change throughout the month depending on the phase of the menstrual cycle. For example rising estrogen in the follicular and ovulatory phase makes women more sensitive to insulin, giving women a metabolic advantage over men and post menopausal women. Calorie needs in the luteal phase increase under the action of progesterone and the body becomes more insulin resistant. As estrogen and progesterone fluctuate, women respond differently to fasting within one menstrual cycle alone and therefore shoul adjust eating behaviours to align with the menstrual cycle. You can read more about eating in alignment with the menstrual cycle in my book “Eating for Hormone Balance” which you can purchase here .
Time restricted eating offers a gentle approach to intermittent fasting that is more suitable to the physiology of a woman while still giving all the benefits of intermittent fasting. Based on my understanding “time restricted eating” is a new term used in the scientific literature to help differentiate what appears to be the most beneficial form of eating and fasting for overall health (both men and women). It is important to consult with a healthcare professional before adopting any significant changes to your eating patterns, especially if you have underlying health conditions or are pregnant or breastfeeding.
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