Intermittent fasting 101
I recommend two types of fasting depending on a woman’s age + stage of life.
- time-restricted eating: eating during a 8-12 hour food window [taking a 12-16 fast from food]
- caloric restriction: a 24 hour fast where minimal calories are consumed
I recommend time-restricted eating for every woman who comes into my practice as a daily ritual. Not only is this pattern of eating very approachable + easy to follow, it allows the digestive system a time of rest resulting in optimized sleep, improved blood sugar regulation, improved gut health and weight loss. Depending on comfort level, schedule + how each woman’s body feels, their eating window can range anywhere from 8 hours [taking a 16 hour fast from food] to 12 hours [taking a 12 hour fast from food]. As long as women are able to meet their nutrient requirements during whichever eating window they choose [letting hunger cues be their guide], I let their intuition lead them to a place that feels right for them.
Minimal calorie intake during a 24-hour period of time brings the body into a state of light ketosis. This switch from burning glucose as fuel [the body’s preferred energy source] to fat as fuel is a practice in metabolic flexibility [think of it as weightlifting for the metabolism!]. Becoming more metabolically flexible has amazing impacts on metabolism + overall health including:
- increased insulin sensitivity
- reduced inflammation
- weight loss
- increased longevity
- improved microbiome diversity
To optimize the benefits of caloric restriction, I recommend low-intensity [heart rate < 140 bpm] or no exercise in order to reduce physical stress on the body and gain as much as you can from this practice. As long as women are meeting their nutrient needs throughout the week, I recommend caloric restriction 1-2 days per week with a few caveats depending on age + stage of life.
caloric restriction during pre-menopause
For cycling women I recommend fasting 1-2 days per week only during the follicular phase + after bleeding has stopped [roughly days 5-14 of the cycle]. This is when energy levels are higher and the body is more resistant to physiological + environmental stressors. Women may also find their food cravings are diminished during this phase, making fasting more manageable + beneficial.
The luteal phase [roughly day 14 – the start of bleeding] is when the body is preparing the uterine wall to nurture + support a potential baby. Because of this, energy needs are higher + women are slightly more insulin resistant. Fasting during this time not only causes women to be irritable, it puts unnecessary stress on the body and hormones. caloric restriction during perimenopause Fasting is an incredibly beneficial practice for women in perimenopause to increase the body’s sensitivity to insulin + optimize metabolism. However, because cycles + hormones during perimenopause fluctuate often, I always recommend letting a woman’s body be her guide. If cycles are still predictable, I recommend practicing caloric restriction only during the follicular phase and refraining during the luteal phase of the cycle for the reasons mentioned above. If cycles are unpredictable, I encourage women to tune into what their bodies are craving during this time. If fasting in the form of caloric restriction feels stressful, I recommend taking a break and trying again in a couple of weeks. Tracking symptoms in a symptom tracker during perimenopause can be incredibly helpful in deciphering hormonal fluctuations / stages of the cycle to learn when fasting might be the most beneficial.
caloric restriction for post-menopausal women
Women who have entered the sacred post-menopausal stage of life are free to practice caloric restriction 1-2 days per week as often as they would like, making sure to tune into their body for cues on what it needs + craves on a day by day basis.
You may find that fasting is easier // harder during different seasons of the year. In the heart of summer with lots of social engagements + later nights, I lengthen my eating window and take a break from caloric restriction. In the winter where the days are shorter + my social calendar slows down, I lean into a shorter eating window + 1-2 days of caloric restriction per week.
who should not fast?
Because fasting is a form of stress, it is important to reserve fasting for times when your body is in an optimal state [and ready to be stressed]. If you are sick, pregnant, nursing, emotionally fragile, or training for an athletic event, pause from any type of fasting and listen to the gentle nudges of what your body needs during this time.
Above all, be gentle with yourself! Fasting is a way to love, not punish, your body.
what about women on birth control?
For cycling women on birth control, my recommendations mirror those for post-menopausal women [see above]. does fasting impact fertility? Multiple day [extended] fasts DO pose a threat to women’s reproductive hormones and can lead to decreased fertility. Similarly, if a woman is not meeting her nutrient needs throughout the week [even without fasting] OR is metabolically unhealthy, fertility can be impacted. If a woman’s body is under lots of physical [or emotional!] stress, it will be more interested in preserving her life than creating + nurturing another one.
However, if a woman who is trying to conceive incorporates caloric restriction during the follicular phase of her cycle 1-2 days per week, is meeting her nutrient needs throughout the remainder of the week, and is only fasting during times of optimal health, fertility will not be negatively impacted. Instead, caloric restriction is a great way to improve metabolic health so that the needs + life of a future baby can be supported!
- time-restricted feeding and the microbiome
- benefits of metabolic flexibility
- obesity and disruptions of female fertility
- intermittent fasting and reproductive hormone levels
- intermittent fasting and cancer
- intermittent fasting and metabolic health