Intermittent Fasting: Will It Affect Your Hormones?

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  • Research has found that short-term body changes occur while performing intermittent fasting.
  • Intermittent fasting may affect hormone levels in both men and women.
  • Intermittent fasting is not a “one-size fits all” diet.
  • Long-term effects of intermittent fasting are not yet fully understood.

What is Intermittent Fasting?

Intermittent fasting has been popular in diet culture over the past few years. But what is intermittent fasting? And what does it do to your body?

Intermittent fasting is a strategic eating pattern where you have alternating periods of eating or fasting. This is different from calorie restriction diets because you do not focus on what or how much you eat, only when you eat.

A great example of intermittent fasting can be seen in Islamic culture. During this holy month, Muslims around the world observe a fast from sunrise until sunset, refraining from food, water, and other indulgences. Beyond its spiritual significance, Ramadan serves as a beautiful illustration of discipline, community, and self-reflection.

In the past, conflicting evidence has been published about how intermittent fasting affects your body. Luckily, over the last few years, thorough scientific reviews have been published. Scientific reviews are articles that assess hundreds of research studies to make meaningful recommendations.

These reviews have found that intermittent fasting could lead to short-term effects like:

– Blood pressure reduction
– Fat mass reduction
– Improvements in insulin sensitivity
– Changes in hormone secretion
– Changes in metabolic function

However, different types of intermittent fasting may cause different changes to your body.

Types of Intermittent Fasting

Many types of intermittent fasting have been studied. In each section below, we will:

1) Describe the type of intermittent fasting
2) Review the findings of intermittent fasting studies
3) Uncover how each type of intermittent fasting may affect your hormones

Time-Restricted Feeding

Time-restricted feeding is a form of fasting that will last 12-20 hours each day.

A key review assessed 19 studies on time-restricted feeding. Ten of the studies assessed healthy populations. Nine assessed populations with metabolic disorders.

According to the review, time-restricted feeding reduced fat mass in all populations. More importantly, time-restricted feeding appeared to be effective at treating metabolic disorders. In people with metabolic disorders, time-restricted feeding caused short-term effects like reductions in:

– Fat mass
– Weight
– Systolic Blood Pressure
– Triglycerides

This leads us to our next question. Does time-restricted feeding affect hormones?

There is little research about how time-restricted feeding affects hormones in any population.

In one study, time-restricted feeding reduced testosterone and insulin-like growth factor 1 in men. Despite this, muscle mass did not decrease.

Another study assessed if time-restricted feeding helps women with polycystic ovary syndrome (PCOS).

Women with PCOS produce a high amount of male sex hormones, like testosterone. Long and painful periods are one crippling symptom of PCOS.

In that study of women with PCOS, testosterone was reduced with time-restricted eating. Eleven out of fifteen women experienced improvements in length and amount of pain during menstruation.

Although the number of participants was low, this study suggests intermittent fasting could benefit women with hormone imbalance.

More research is needed to understand if time-restricted feeding can effectively treat or prevent disease.

5:2 Intermittent Fasting

One study defines “5:2 intermittent fasting” as spending 5 days of the week eating normally and restricting calorie intake on 2 non-consecutive days. For the 2 days of “fasting”, people restrict their diet to 500 or 600 calories. Another method of 5:2 fasting is where the “2” means 2 non-consecutive days of full fasting.

In a 2021 study, 300 adults took part in a randomized controlled trial. Many found it hard to complete one year of 5:2 fasting. Nearly 70% of participants stopped the diet before the 6-month mark.

For those who continued the diet for up to one year, most saw weight loss of 5%. Another study found that 6 months of 5:2 fasting reduced blood pressure, cholesterol, and body weight.

Now, does 5:2 fasting affect your hormones?

There are only a few research studies that assess how 5:2 fasting affects hormones. But one key study in premenopausal women reported some interesting findings.

In premenopausal women, 5:2 fasting for 6 months reduced:

– Insulin levels
– Leptin
– C-reactive protein.

However, it did not appear to affect testosterone or other sex hormones.

It is important to note that this study only looked at healthy women. More research is needed to understand if 5:2 fasting could benefit women or men with hormone imbalances.

Alternate Day Fasting

Alternate Day Fasting

Alternate-day fasting is a form of intermittent fasting that alternates between 24 hours of fasting and 24 hours of eating freely.

One scientific review found that, in the short-term, alternate-day fasting reduced:

– Cholesterol
– Blood Pressure
– Triglycerides
– Fat Mass
– Weight

There were no studies directly reporting the effects of alternate-day fasting on hormones. However, one study reported that fasting for 24 hours can change the levels of thyroid hormones present in your body.

More research is needed to understand how alternate-day fasting can affect your body’s hormones in the long term.

Who Should Avoid Intermittent Fasting?

Intermittent fasting is not for everyone.

It is recommended that some avoid intermittent fasting altogether. These populations include:

– Women who are pregnant or breastfeeding
– Children and teens under 18 years of age
– People with Type 1 Diabetes
– People with a history of eating disorders
– People with seizure disorders
– Those taking medications that must be taken with food

Intermittent fasting is not for everyone. Be sure to listen to your care providers about their recommendations for your diet and lifestyle.

Conclusion & Future Intermittent Fasting Research Needs

The published research discusses the short-term effects, and there may be several. Studies have found that intermittent fasting can:

– Decrease blood pressure, weight, fat mass, and triglycerides
– Decrease hormone levels of testosterone and insulin-like growth factor-1

It is important to know that these effects were reported while people were performing intermittent fasting. It is unclear if these effects will continue if intermittent fasting is stopped.

We do not have a good understanding about whether there are beneficial or harmful long-term effects of intermittent fasting. Most studies assessed intermittent fasting for 3-6 months. Intermittent fasting for years may have other positive or negative effects that we are unaware of.

The National Institute on Aging reported that intermittent fasting could improve metabolic disorders. But it may not benefit normal, healthy adults.

The National Institute on Aging reported that the longest study on intermittent fasting was for 2 years.

This tells us that the long-term effects of intermittent fasting are unknown, and more research is needed before we know if long-term intermittent fasting has positive or negative effects.

Future research of intermittent fasting should assess:

1) Long-term effects on major organs like the brain, liver, heart, and more
2) If intermittent fasting could effectively treat hormonal imbalance
3) How stopping intermittent fasting affects the body
4) If one type of intermittent fasting works better than others

Always be sure to check with your doctor before making a lifestyle change like this one. It is not advisable to begin without ensuring that it is a safe choice.

You can learn more about the science of intermittent fasting and the potential effects on hormone imbalance at the Fast Like a Girl Summit. More than 40 experts in nutrition were interviewed by Mindy Pelz, DC, and Kashif Khan. Don’t miss out on these unique and informative interviews!

DrTalks Video Resources about Intermittent Fasting

About the Author – Daniel Chantigian

Dive into the world of chronic diseases and other health conditions with writings by Daniel Chantigian, MS. Discover groundbreaking research and enlightening disease summaries through his works on our blog:

Intermittent Fasting References

Moon, S., Kang, J., Kim, S. H., Chung, H. S., Kim, Y. J., Yu, J. M., Cho, S. T., Oh, C. M., & Kim, T. (2020). Beneficial Effects of Time-Restricted Eating on Metabolic Diseases: A Systemic Review and Meta-Analysis. Nutrients, 12(5), 1267. Read it here.

Moro, T., Tinsley, G., Bianco, A., Marcolin, G., Pacelli, Q. F., Battaglia, G., Palma, A., Gentil, P., Neri, M., & Paoli, A. (2016). Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males. Journal of translational medicine, 14(1), 290. Read it here.

Li, C., Xing, C., Zhang, J., Zhao, H., Shi, W., & He, B. (2021). Eight-hour time-restricted feeding improves endocrine and metabolic profiles in women with anovulatory polycystic ovary syndrome. Journal of translational medicine, 19(1), 148. Read it here.

Hajek, P., Przulj, D., Pesola, F., McRobbie, H., Peerbux, S., Phillips-Waller, A., Bisal, N., & Myers Smith, K. (2021). A randomised controlled trial of the 5:2 diet. PloS one, 16(11), e0258853. Read it here.

Harvie, M. N., Pegington, M., Mattson, M. P., Frystyk, J., Dillon, B., Evans, G., Cuzick, J., Jebb, S. A., Martin, B., Cutler, R. G., Son, T. G., Maudsley, S., Carlson, O. D., Egan, J. M., Flyvbjerg, A., & Howell, A. (2011). The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomized trial in young overweight women. International journal of obesity (2005), 35(5), 714–727. Read it here.

Cui, Y., Cai, T., Zhou, Z., Mu, Y., Lu, Y., Gao, Z., Wu, J., & Zhang, Y. (2020). Health Effects of Alternate-Day Fasting in Adults: A Systematic Review and Meta-Analysis. Frontiers in nutrition, 7, 586036. Read it here.

Basolo, A., Begaye, B., Hollstein, T., Vinales, K. L., Walter, M., Santini, F., Krakoff, J., & Piaggi, P. (2019). Effects of Short-Term Fasting and Different Overfeeding Diets on Thyroid Hormones in Healthy Humans. Thyroid : official journal of the American Thyroid Association, 29(9), 1209–1219. Read it here.

Hear from 40+ Experts to Discover How Fasting and Diet Variation can Boost Your Energy, Power Up Your Brain, and Achieve Your Weight Loss goals at the Fast Like a Girl Summit!

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Daniel Chantigian
Daniel Chantigian, MS
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When it comes to complex scientific or medical topics, Daniel can successfully communicate with any audience via writing, social media, lecturing, and one-on-one discussions. Over the past decade, he developed these skills as a researcher at the University of Minnesota and the Mayo Clinic, as a lecturer at the University...

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