Are you a woman looking to try a fasting diet? How can you fast based on your hormonal cycle?
In Fast Like a Girl, Mindy Pelz suggests that you can establish and maintain hormonal balance by following her fasting schedule. She recommends a schedule that’s divided into four phases based on your cycle.
Check out Fast Like a Girl‘s schedule that’ll help women fast safely.
Align Your Fasting Schedule With Your Hormonal Cycle
If you have a regular menstrual cycle, start Fast Like a Girl‘s schedule on your first day of bleeding and follow it until your next period. If your cycle is irregular or nonexistent due to factors like birth control, stress, or menopause, start when you want and follow a 30-day continuous schedule. (Shortform note: Some nutritionists have raised concerns about Pelz’s fasting advice due to its lack of supporting research and references. Further, these critics warn that Pelz oversimplifies hormonal health, which could inadvertently lead her followers to compromise their health. Follow her advice at your own discretion.)
Pelz divides the hormonal cycle into four phases, providing fasting and dietary advice for each. Let’s explore the specifics of each phase.
Phase #1: Days 1 to 10
On day one of your hormonal cycle, when bleeding begins, estrogen, testosterone, and progesterone levels are at their lowest. Your body starts building its estrogen stores to prepare for a new round of ovulation.
Pelz says that estrogen supports the production of:
- Collagen, which helps maintain the connective tissue that supports skin, teeth, bones, cartilage, and organs
- Pleasurable neurotransmitters such as serotonin and dopamine that help you feel calm and positive
(Shortform note: Estrogen also impacts cholesterol levels, circulation and blood flow, and the ability to focus. Symptoms of consistently low estrogen levels include breast tenderness, vaginal dryness, brittle bones, night sweats, irregular periods, headaches, fatigue, sleep problems, and depression. Signs of consistently high estrogen levels include weight gain, irregular periods, heightened premenstrual symptoms, and decreased sex drive.)
Estrogen production improves when blood sugar and insulin levels are low. Pelz suggests that you can keep these levels low and support the production of estrogen by following the following fasting routine: On days one to four, fast for 13 hours; on day five, fast for 15 hours; and on days six to 10, fast for 17 hours.
(Shortform note: While Pelz asserts that estrogen production thrives when blood sugar and insulin levels are low, research paints a mixed picture. One study aligns with her argument, suggesting that higher blood sugar levels alter hormone metabolism, resulting in decreased estrogen production. However, some nutritionists argue that the relationship is the other way around: Higher blood sugar and insulin levels generate more fat cells—and fat cells secrete estrogen—therefore, increased blood sugar and insulin levels can increase estrogen levels.)
During each of these days, consume a maximum of 50 grams of complex carbohydrates (to keep blood sugar and insulin levels low) and up to 75 grams of protein. Pelz also suggests that more than 60% of your food should be in the form of “good” fats, specifically those naturally high in cholesterol.
(Shortform note: Pelz refers to this diet as “ketobiotic,” the term she coined for her adaptation of the standard ketogenic diet. While maintaining the high-fat, moderate-protein, and low-carb principles, she distinguishes her version of the diet by including complex carbohydrates and prebiotic foods that support a healthy gut microbiome—a component not typically prioritized in the standard ketogenic diet. Yet, while Pelz recommends eating “good” fats high in cholesterol, she doesn’t specify what these are. According to experts, you need to aim for monounsaturated fats (sources include nuts, nut oils, avocados, and olives) and polyunsaturated fats (sources include seeds, walnuts, fatty fish, fish oil, soybean, soymilk, and tofu).)
Phase #2: Days 11 to 15
During days 11 to 15 of your cycle, when ovulation occurs, your estrogen levels reach their peak and your testosterone levels elevate. Testosterone supports muscle growth and increases motivation and energy. According to Pelz, testosterone production thrives when you feel calm; therefore, removing potential stressors from your life helps maintain healthy levels. (Shortform note: Research supports the beneficial effects of testosterone that Pelz describes. However, while Pelz suggests that stress reduction leads to healthy testosterone levels, studies show that individual reactions to stress vary, with some women experiencing increases in testosterone levels and others experiencing decreases.)
On these days, Pelz recommends that you help your body metabolize the hormones it has been producing. This ensures your cells effectively assimilate these hormones and prevents the accumulation of unmetabolized hormones in your tissues—which, according to Pelz, is the primary cause of uncomfortable premenstrual symptoms like mood swings, weight gain, night sweats, and sore breasts.
(Shortform note: Research clarifies why it’s important to metabolize hormones. When hormones are not properly metabolized, they don’t exit the body. Instead, they recirculate in the bloodstream and gradually accumulate in various tissues. This accumulation can overstimulate hormonal receptors, creating hormonal imbalances that can lead to a variety of health issues—from the premenstrual symptoms Pelz describes to more severe conditions such as fertility problems and hormone-dependent cancers.)
Two organs responsible for hormone metabolism are the liver and gut. Therefore, Pelz recommends prioritizing foods that nourish these organs, such as root vegetables and fruits. Stick to a daily allowance of 150 grams of complex carbohydrates (the increase allows for more fruit and vegetables), 50 grams of protein, and as much “good” fat as you want.
(Shortform note: Your liver and gut play a key role in many bodily functions, including hormone metabolism. Dieticians clarify that root vegetables such as beets and carrots contain plant flavonoids and antioxidants that support your liver and gut by reducing cell damage and inflammation. Meanwhile, fruits such as grapefruit and blueberries are high in vitamin C and polyphenols, which help to neutralize toxins and protect cells.)
Additionally, Pelz advises against fasting for longer than 15 hours on each of these five days. (Shortform note: While research on how fasting impacts hormone metabolism is in the early stages, existing studies indicate that fasting can disrupt hormonal circadian rhythms, which might interfere with hormone metabolism. Therefore, limiting the duration of fasts during this phase may help maintain these rhythms and support hormone metabolism.)
Phase #3: Days 16 to 18
During days 16 to 18 of your cycle, your hormone levels dip, which might cause your energy levels to drop. Pelz suggests that you fast for 15 hours each of these days, and follow the dietary guidelines provided for Phase #1. (Shortform note: In medical terms, this phase of the menstrual cycle is commonly referred to as the early luteal phase. During this time, insulin sensitivity starts to decrease. Therefore, Pelz’s nutritional and fasting advice should keep your blood sugar in balance, preventing blood sugar spikes that decrease energy levels even further. Additionally, experts note that your body temperature may be high from ovulation—they recommend reducing your exercise intensity to prevent overheating.)
Phase #4: Day 19 Until Bleeding Begins
On day 19 of your cycle, your body begins producing progesterone. This hormone prepares your uterus to receive a fertilized egg. If fertilization doesn’t occur, progesterone and estrogen levels decrease as your uterus readies itself to shed its lining and start menstrual bleeding (the beginning of the next cycle).
Pelz emphasizes that insufficient progesterone can lead to uncomfortable symptoms, such as irregular menstrual cycles, spotting, heightened irritability, and sleep difficulties. (Shortform note: It’s worth noting that the same symptoms can also signify excessively high progesterone levels.)
To support healthy progesterone levels during this phase, she recommends that you avoid fasting until your next cycle begins (or, if you don’t have a cycle, until the 30 days are up). There are two reasons for this. First, stress decreases progesterone levels (fasting creates hormetic stress). Second, progesterone thrives on higher blood sugar and insulin levels, which fasting tends to decrease. Additionally, she suggests that you follow the dietary guidelines provided for Phase #2.
(Shortform note: While research in this area is limited, dieticians tend to agree that it’s best not to fast during this phase to prevent stress and encourage progesterone production. They also caution against restricting calories, as that too can create stress that disrupts progesterone production. Therefore, when following Pelz’s dietary guidelines, ensuring you don’t drastically cut your calorie intake might help keep your progesterone levels in balance.)
