What is Intermittent Fasting?
Intermittent fasting has become quite a common practice for health and well-being. It involves restricting energy consumption to certain periods, so that you have alternating periods of fasting and normal food consumption within either a day or a week.
There are a number of popular ways to do this, which differ in the intensity and frequency of the fasting period:
- The 5/2 diet involves two days per week of restricted calorie intake (roughly 500-600 calories a day), whilst on the remaining five days a normal diet is maintained.
- The 16/8 diet restricts the time in a day in which you can eat to eight hours. Usually, people on this diet fast between dinner and lunchtime the next day.
- The 24-hour fast involves choosing one or two days a week in which no calories are consumed at all. This may be from after dinner on one day until dinner the next day.
It is thought that intermittent fasting has a number of health benefits. Studies have shown that it is a powerful practice to help people lose weight, that it has the potential to decrease the risk of cancer, and that it improves cognitive performance. Whilst these results are promising, however, further studies are required before their findings are confirmed.
Does Intermittent Fasting Increase Testosterone?
Unfortunately, the research into the link between intermittent fasting and testosterone has not yet revealed a clear picture. Whilst studies seem to suggest that fasting impacts upon the process that produces the male hormone, there is not yet a consensus on whether it increases that hormone or, in fact, decreases it.
One study that is often cited to support the idea that fasting boosts testosterone is from 1989. Nine obese men and eight non-obese men were included in the study, which investigated the effect of overnight fasting on the luteinising hormone (LH) – a hormone crucial to testicular function and the production of testosterone. Whilst no effect was found in obese men, fasting increased LH by 67% in non-obese men, which gave a corresponding testosterone boost of 180%.
Whilst that’s not to be sniffed at, the small sample size does not make for a hugely reliable study. Meanwhile, other studies have failed to corroborate its findings. One, investigating the effect of fasting on LH and testosterone, found that both of these hormones decreased after periods of restricted energy consumption. A more recent study found again that energy restriction actually led to a decrease in testosterone levels.
Unfortunately, despite one promising study, the relationship between intermittent fasting and testosterone is far from being confirmed by the science. However, you may benefit from the other effects that this health practice offers.
How Does Intermittent Fasting Affect Other Hormones?
Whilst intermittent fasting does not promise any certain results for your testosterone levels, that’s not to say that it has no impact on your hormonal balance at all. Rather, evidence suggests that energy consumption and hormone levels are, in some cases, closely linked.
Insulin
One of the most significant effects of intermittent fasting is that which is had upon insulin levels and insulin resistance. Insulin is the hormone, produced by the pancreas, that controls blood sugar levels and that allows you both to use sugar from foods and to store it.
Fasting seems to improve insulin resistance – i.e. the problem in which your body struggles to use blood sugars – and reduces the overall risk of type 2 diabetes, according to one study. Similarly, a study found that diabetics who fasted did not have such a great need of treatment with insulin.
Human Growth Hormone
The human growth hormone (HGH) – or somatotropin – is responsible for many different processes in the body, from body composition and cell growth and repair to exercise performance, strength, and recovery from illness.
Whilst it is a hormone that some athletes inject artificially, evidence suggests that intermittent fasting can boost this hormone naturally. In one study, after two days of fasting, HGH had increased on average by 500%. A similar study also found that levels of growth hormone increased after a period of fasting.
Leptin, Ghrelin, and Adiponectin
Alongside insulin, which regulates blood sugar levels, intermittent fasting appears to affect the levels of other hormones crucial to your body’s maintenance of energy levels and the storage of fat. These are leptin, ghrelin, and adiponectin.
Colloquially, leptin is known as the “satiety hormone”, as it tells your brain when you are full. Ghrelin, the “hunger hormone”, is the signal your body gives when you are hungry. In people who are overweight or obese, these hormones can be imbalanced, meaning that you do not respond to the signs that you are full, for example.
Evidence seems to suggest that time-restricted eating reduces ghrelin levels and therefore decreases the desire to eat. Meanwhile, some studies suggest that leptin increases with fasting – thus increasing your feelings of fullness too.
Let’s not forget adiponectin, a hormone that is crucial to your energy metabolism and that is thought to be useful for the treatment of obesity. This increases significantly as a result of fasting.
Key Takeaways
No link between intermittent fasting and testosterone has yet been confirmed, with studies to date having given contradictory results. There are, however, promising signs that this eating regime does have positive effects on different hormones, including the human growth hormone and insulin.
Meanwhile, the other health benefits that intermittent fasting promises may convince you to try it nonetheless.
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³Röjdmark S. (1987). Influence of Short-Term Fasting on the Pituitary-Testicular Axis in Normal Men.
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⁵Suleiman Furmli, Rami Elmasry, Megan Ramos and Jason Fung (2018). Therapeutic use of intermittent fasting for people with type 2 diabetes as an alternative to insulin.
⁶Harvard Men’s Health Watch (2021). Growth hormone, athletic performance, and aging.
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¹⁰Salah Kassab, Tarik Abdul-Ghaffar, Das S Nagalla, Usha Sachdeva, Usha Nayar (2004). Interactions between leptin, neuropeptide-Y and insulin with chronic diurnal fasting during Ramadan.
¹¹Ersilia Nigro, Olga Scudiero, Maria Ludovica Monaco, Alessia Palmieri, Gennaro Mazzarella, Ciro Costagliola, Andrea Bianco and Aurora Daniele (2014). New Insight into Adiponectin Role in Obesity and Obesity-Related Diseases.
¹²Sadegh Feizollahzadeh, Javad Rasuli, Sorayya Kheirouri and Mohammad Alizadeh (2014). Augmented Plasma Adiponectin after Prolonged Fasting During Ramadan in Men.
¹³Adrienne R.Barnosky, Kristin K.Hoddy, Terry G.Unterman, Krista A.Varady (2014). Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings.
