What Happens To Your Body When You Fast?

Our ancestors didn't need a podcast to tell them fasting was good for them. They just did it naturally as part of their lives.

Right now, over two billion people around the world are fasting. Muslims are deep into Ramadan. Christians are observing Lent. And whether or not you follow a faith tradition, there's something worth paying attention to here — because our ancestors across every culture, every continent, and every era understood something that modern science is only now catching up to:

Going without is what can make a man stronger.

We Were Never Meant to Eat Six Times a Day

Think about the men who came before you. Your great-great-grandfather didn't wake up to a protein shake and a mid-morning snack bar. He ate when food was available and went without when it wasn't. His body was built for it. Your body is built for it.

A landmark review published in The New England Journal of Medicine by researchers from the National Institute on Aging and Johns Hopkins University put it plainly: eating in a 6-hour window and fasting for 18 hours can trigger a metabolic switch from glucose-based to ketone-based energy, leading to increased stress resistance and decreased incidence of disease^[1].

Somewhere along the way, we got sold the idea that we needed to eat constantly — that skipping a meal was dangerous, that hunger was the enemy. The supplement industry (yes, our industry) played its part in that. Eat every three hours. Take this pre-workout. Take this post-workout. Never let your body go without.

But the truth is our body does some of its best work when we stop constantly grazing and feeding it.

What Actually Happens When You Fast

The research on fasting, particularly intermittent fasting and extended fasts — is extensive, published in peer-reviewed journals, and growing every year. Here's what the evidence shows.

1. Your Body Starts Cleaning House

After roughly 12–16 hours without food, your body triggers a process called autophagy — from the Greek auto (self) and phagein (to eat). Your cells literally start breaking down and recycling damaged components. Think of it as your body's built-in maintenance system. It clears out the cellular debris that accumulates from stress, poor sleep, and environmental toxins.

Yoshinori Ohsumi won the 2016 Nobel Prize in Physiology or Medicine for his discoveries of the mechanisms underlying autophagy^[2]. His work using baker's yeast identified 15 essential genes involved in the process, revealing that the same cellular recycling machinery operates in human cells^[3]. Since his breakthrough, autophagy research has exploded from fewer than 20 papers per year to over 5,000, spanning cancer, longevity, neurodegeneration, and immunity^[4].

A 2023 study published in Science Direct examined healthy young males during Ramadan fasting (17–19 hours daily) and found that prolonged intermittent fasting significantly affected autophagy gene expression, with autophagy-related genes showing upregulation that peaked during mid-fasting — confirming that this style of fasting activates the body's cellular cleanup mechanisms^[5].

2. Growth Hormone Surges

Research published in the Journal of Clinical Investigation demonstrated that fasting profoundly enhances growth hormone secretion through both increased pulse frequency and amplitude^[6]. A 2025 randomised controlled trial published in Frontiers in Endocrinology confirmed that even a single 24-hour water-only fast significantly increases human growth hormone (HGH) levels, independently of weight loss — with individuals who had lower baseline HGH experiencing the most dramatic increases^[7].

A separate analysis published in npj Metabolic Health and Disease reported that 24-hour fasting can produce a 5- to 14-fold rise in HGH in males and females respectively^[8].

HGH plays a critical role in muscle preservation during fasting. Research published in the Journal of Clinical Endocrinology & Metabolism showed that growth hormone is a decisive component of protein conservation during fasting, and that the underlying mechanism involves a decrease in muscle protein breakdown^[9]. In other words, your body doesn't eat your muscle during a fast — it protects it.

3. Your Brain Gets Sharper

Fasting increases production of brain-derived neurotrophic factor (BDNF), a protein that supports the growth of new neurons and strengthens existing ones. A review published in Ageing Research Reviews by the National Institute on Aging confirmed that intermittent fasting results in increased BDNF production, which increases the resistance of neurons to dysfunction and degeneration^[10].

A systematic review of 82 peer-reviewed papers found that BDNF has emerged as a key regulator of cognitive performance and brain health, with aging-related loss of BDNF associated with reduced synaptic plasticity, impaired memory and learning, and increased risk of cognitive impairment and Alzheimer's disease^[11].

The mechanism is elegant: during fasting, the ketone body beta-hydroxybutyrate stimulates BDNF gene expression in neurons, essentially using the metabolic shift triggered by fasting to upregulate the brain's own growth and repair signals^[12].

4. Inflammation Levels Drop

Chronic low-grade inflammation is behind almost every modern disease — heart disease, metabolic syndrome, joint pain, brain fog. A meta-analysis of 21 trials (839 participants) published in Nutrients found that intermittent fasting significantly reduced TNF-α, CRP, and leptin — three key inflammatory markers^[14].

Research specifically on Ramadan fasting is compelling. A study published in Annals of Nutrition and Metabolism found that IL-6 and CRP levels were significantly reduced during Ramadan fasting compared to pre-Ramadan baseline values, with positive effects on cardiovascular risk factors^[15]. A separate systematic review and meta-analysis found that Ramadan fasting significantly reduces IL-6, TNF-α, and CRP in both overweight and non-obese individuals^[16].

It's important to note that the evidence is nuanced — some studies on prolonged fasting (48+ hours) have found temporary increases in certain inflammatory markers that normalise after refeeding, suggesting this may be an adaptive response rather than harm^[17]. But for the kind of intermittent fasting most people practice (16:8, Ramadan-style dawn-to-sunset), the anti-inflammatory evidence is encouraging.

5. Insulin Sensitivity Improves

When you fast, your insulin levels drop significantly. This gives your cells time to resensitise to insulin, which means better blood sugar regulation and more stable energy throughout the day.

A GRADE-assessed systematic review and meta-analysis of randomised controlled trials found that fasting significantly decreased fasting blood glucose, HbA1c (a measure of long-term blood sugar control), and HOMA-IR (the gold standard for measuring insulin resistance)^[18].

A controlled feeding trial at Pennington Biomedical Research Center — the first of its kind — demonstrated that early time-restricted feeding improved insulin sensitivity, blood pressure, and oxidative stress in men with prediabetes even without any weight loss^[19]. A 26-week randomised trial showed that intermittent fasting substantially reduced insulin resistance, independent of significant weight change^[8].

In a world where metabolic disease is the leading killer of men, this alone is reason enough to consider fasting.

6. What About Testosterone?

A review of human trials published in Nutrients found that intermittent fasting reduced testosterone levels in lean, physically active young males — though importantly, muscle mass and strength were not negatively affected by these reductions^[20]. Research on Ramadan fasting also showed decreases in testosterone over the fasting period^[21].

However, for men carrying excess body fat, the picture may be different. Excess body fat contains aromatase, an enzyme that converts testosterone to oestrogen. By improving insulin sensitivity, reducing body fat, and improving metabolic health, fasting may indirectly support healthier testosterone levels in overweight men^[22].

7. The Spiritual Dimension Matters Too

Here's something the modern wellness space often misses: fasting has always been about more than the body.

Ramadan and Lent aren't just about abstaining from food and water during daylight hours. It's about discipline. Gratitude. Proving to yourself that your desires don't control you. Lent carries the same principle — voluntary sacrifice as a path to something greater.

Whether or not you're religious, there's deep value in voluntarily choosing discomfort. Every time you feel that hunger pang and choose not to act on it, you're training the same mental muscle that helps you stay disciplined in the gym, focused at work, and present with your family.

Our ancestors understood this intuitively. Fasting wasn't a "biohack." It was a practice of self-mastery.

A Note From Our Founder

Can I Take ATHANASE While Fasting?

We get asked this a lot . Here's the straight answer:

How to Start Fasting (If You Haven't Already)

You don't need to jump into a 72-hour water fast. Start where you are. Mark Mattson, the neuroscientist whose NEJM review helped bring fasting research into the mainstream, advises that people gradually increase the duration and frequency of fasting periods over several months rather than going cold turkey^[1]. So here are three options to try:

ATHANASE® — The Foundation For The Other 11 Months

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The Bottom Line

Fasting is about giving your body the space to do what it was designed to do — repair, adapt, and come back stronger.

Two billion people are doing it right now for reasons that go back thousands of years. The science backs it. The tradition backs it. And your own experience will back it too, once you try.

Stop eating for a while. See what happens.

Make Your Ancestors Proud! ⚔️