Intermittent fasting is not a diet per se, but rather an eating pattern that alternates between periods of eating and fasting. This cyclical approach taps into the body’s natural metabolic processes, promoting various physiological changes. The primary methods of intermittent fasting include the 16/8 method (16 hours of fasting and an 8-hour eating window), the 5:2 diet (two non-consecutive days of very low-calorie intake), and the eat-stop-eat method (24-hour fasting periods once or twice a week). The most common pattern is the 16/8 method. 

What happens when we fast?

It’s important to point out that fasting can have various effects on the body at different time intervals. Individual responses may vary, and these generalizations may not apply to everyone. 

Fasting zero-to-one-hour results in the post-prandial state, with elevated blood sugar levels. Insulin is released to help the cells take up glucose for energy storage. By hour three, the blood sugar and insulin levels have begun to decline. The body transitions from using sugar for energy to using stored glycogen from the liver. During this time you may begin to feel hunger sensations. At the fifth hour, glycogen stores in the liver are depleted, leading to a more significant reliance on fat for energy and insulin levels continue to decrease. Around the seventh fasting hour, fatty acids are released from fat cells and transported to the liver for energy production. Ketone production begins because of fat metabolization. During the ninth hour, ketosis continues, and insulin sensitivity may improve. After twelve hours of fasting, a cellular clean-up process called autophagy begins while insulin levels are low, promoting fat breakdown. At sixteen hours, ketosis and autophagy are still occurring with improved blood sugar levels and insulin sensitivity. After twenty-four hours of fasting, autophagy continues, and growth hormone is released. There is a significant shift towards fat metabolization currently and this is typically when the sensation of hunger starts to dissipate. After thirty-six hours, the cellular repair process is enhanced, and more ketones are being produced through ketosis. At the forty-eight-hour mark of fasting, enhanced mental clarity is reported by some individuals as cellular repair and autophagy continues. 

Breaking Down The Science Behind Intermittent Fasting

‣ Cellular Repair and Autophagy

During fasting, the body initiates autophagy, due to a lack of nutrients. Autophagy begins with the formation of autophagosomes, which engulf old cells, misfolded proteins and damaged cells. This is the process of cellular repair. The autophagosomes will combine with another repair cell, the lysosome, which contains enzyme for breaking down the cells components. This process releases fatty acids and amino acids which are recycled and used to generate more energy or contribute to the formation of new cells.  This process occurs throughout the body and isn’t limited to a single tissue type. 

‣ Insulin Sensitivity

Intermittent fasting helps regulate blood sugar levels by enhancing insulin sensitivity. Fasting leads to a decrease in blood sugar levels which in turn reduces the need for insulin secretion by the pancreas. With lower insulin levels, cells become more sensitive to the hormone when it is eventually released. Also, during fasting, as cells become more reliant on fat for energy, they become more responsive to insulin’s signals making it easier to uptake the sugar into the cells. The reduced levels of fats in the muscles and liver are also associated with improved insulin sensitivity. 

‣ Hormonal Changes

As discussed above, fasting improves insulin sensitivity. It also has a positive impact on human growth hormone. Elevations in human growth hormone has been shown to improve lean body mass and fat metabolism and can support the preservation of muscle mass and stimulate the breakdown of fat for energy. Norepinephrine is a hormone and neurotransmitter that plays a role in the body’s fight or flight response. It is released in response to stress or low blood sugar. During fasting, levels of norepinephrine will increase to mobilize energy resources, including the breakdown of fat for fuel. This elevation can also give the sensation of feeling over stimulated or jittery when you first begin fasting. Another hormone affected by fasting is cortisol, our stress hormone. Short-term fasting will increase cortisol temporarily, long-term fasting results in lower cortisol overall. Adipoenctin is also increased during fasting, and higher levels are associated with improved insulin sensitivity, increased fat metabolization and anti-inflammatory effects. 

The Benefits of Intermittent Fasting for Women

Intermittent fasting can be a practical approach for weight management, as it often leads to reduced calorie intake and improved fat metabolism with preservation of lean muscle mass. Many women note a decrease in weight when they begin to fast. IF may also support hormonal balance in women by positively influencing insulin sensitivity and reducing levels of insulin-like growth factor 1 (IGF-1). Fasting has also been shown to enhance brain function.

The Potential Detriments of Intermittent Fasting for Women

Some women may experience irregular menstrual cycles or disruptions in hormonal levels, especially if intermittent fasting is pursued excessively or without proper nutritional support. Excess stress, nutritional deficiencies, and changes in body weight (especially rapid weight loss) are associated with fasting and can impact the reproductive hormones, menstrual irregularity, and fertility. During perimenopause and menopause, hormonal fluctuations are already occurring. Fasting may exacerbate symptoms such as hot flashes, mood swings, and sleep disturbances. Fasting, especially if it leads to nutrient deficiencies, may impact bone density. Energy levels and mental and emotional well-being may also be affected by fasting due to the hormonal changes and possibility of nutrient deficiencies. 

A Tailored Approach To Intermittent Fasting for Women

Women should adopt intermittent fasting with a personalized approach, considering factors such as age, reproductive status, overall health and the goal or intention of intermittent fasting. Focusing on nutrient-dense foods during eating windows to ensure adequate intake of essential vitamins and minerals is essential for successfully intermittent fasting. Before embarking on an intermittent fasting journey, women should consult with healthcare providers, especially those with pre-existing health conditions or concerns related to reproductive health.

Conclusion

Intermittent fasting can be a powerful tool for women’s health when approached mindfully and with consideration for individual differences. While it offers numerous benefits, it’s essential to acknowledge potential drawbacks and tailor fasting methods to suit the unique needs of women.