How Fasting Effects Hormones

There are several approaches to intermittent fasting (IF), but all options are essentially restricting the times you eat either on a daily or weekly basis. This method of eating shifts your body from running on glucose to utilizing stored fats. Restricted eating has an effect on many hormones, including metabolic, sex, circadian, and stress hormones. See how IF may, or may not be right for you.

Stress Hormones

Cortisol: The adrenal glands release cortisol which rise in the morning and decrease during the day, with surges in response to stress. When blood sugar drops from decreased nutrition, cortisol increases. Research has shown that cortisol increases immediately after a fast, after the fast has ended, and shifts the cortisol peak from morning to when a meal is eaten effecting natural circadian rhythms

What to look for: If you are trying IF, look for changes in increased fatigue, disrupted sleep (especially the 3:00 am wake up), higher blood pressure, gut health, menstrual changes, and weight gain that can be caused by chronically high cortisol levels.

What's different for women: Studies suggest the stress response is higher in women than men. This can be especially relevant in menopause. Low estrogen levels in perimenopausal and menopausal women cause higher cortisol levels, which can further rise with IF. Keep an eye on symptoms that change with ongoing increases in cortisol.

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Sex hormones

Estrogen:  More research is needed to understand how intermittent fasting affects hormones in women. Intermittent fasting may decrease estrogen, this can be impactful if estrogen is already low or possibly helpful in cases of estrogen dominance. If your goal of IF is weight management, keep in mind decreased estrogen can increase appetite and fat storage.  

Low Estrogen Risks: Altered estrogen levels can effect mood, cognition, muscles, digestion, bone formation, and menstruation. Low estrogen increases appetite and fat storage, counteracting some weight management goals of fasting.

Testosterone: Studies have produced mixed results on testosterone levels. One year long study showed "testosterone concentration was significantly reduced after 2 and 12 months of TRE" (time restricted eating).

Generally speaking, lack of nutrients and low fat diets decrease testosterone levels. Pay attention to fatigue, mood changes, weight gain, decreased muscle and bone mass.

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Metabolic hormones

Thyroid hormones regulate metabolism, reaching practically all the cells in your body, converting oxygen and calories in to useable energy.

Research is inconclusive on how thyroid hormones are effected by fasting, but the most significant change seems to be a decrease in T3. Though results are mixed, one study showed a 55% decrease in T3.

T3 is involved with many functions- it helps get oxygen to tissues, increases alertness, regulates reproductive hormones, and enhances gut function. Reduced hormone output might be good news for those managing an overactive thyroid, but dangerous to those with an already sluggish thyroid.

What to look for: If you are doing any kind of ongoing fasting, keep on eye on symptoms that can result from thyroid changes- weight gain, low energy, increased sleep disturbances, menstrual changes, and depression.

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Takeaways

Men and women may have different responses: Based on innate hormone and metabolic differences, woman are more sensitive to stressors. Women show slower metabolism, impaired blood sugar response, and reduced muscle mass compared to men while fasting.

Short versus long term studies: Keep an eye out for new information coming out with long term studies.

Short term studies have shown reduced inflammation, especially in the gut (i.e., IBS, Crohn’s disease) lower inflammatory markers, and break down of damaged cells. 

Long term research showed IF increased risk of dying from heart and circulatory diseases. The American Heart Association shared that IF had a 91% higher risk of dying from heart disease. 

Pay attention to your body: There is a a lot of information on both the benefits and risks of intermittent fasting. If this method is something you are interested in, pay attention to how your body responds. Monitor your emotional and physical health and look for any changes.

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There are many ways to improve energy, manage stress, support metabolism, and enhance overall health. Focus on nourishing your body with quality, whole foods, manage stress, and make sleep a top priority.

Incorporate acupuncture into your healthy lifestyle to help reduce inflammation, balance the nervous system, and support immune function — promoting long-term vitality and well-being.