What Fasting Can Do For Your Health

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Navigating conversations about nutrition is an everyday adventure for me. As a registered dietitian and nutrition expert, I often find myself in one of two scenarios when disclosing my profession. Either I become the recipient of earnest inquiries, as if I were a dispensary of free advice, or I'm thrust into spirited debates about the intricacies of what constitutes good nutrition. After all, everyone consumes food, and with that comes the belief that everyone is an expert. However, unlike personal opinions, science doesn't play favorites; it relies on data and evidence. In the realm of nutrition discussions, I strive to let the science do the talking, allowing evidence-based insights to guide the way.

In my daily discussions, the topic of weight loss often takes center stage. Shedding excess weight offers a multitude of benefits, such as optimizing metabolic function, alleviating markers of inflammation, supporting cellular health, enhancing cognition, promoting longevity, and addressing fertility concerns. The fundamental principle behind successful weight loss is creating a calorie deficit.

One widely employed strategy for achieving this deficit is fasting, whether through intermittent fasting or time-restricted eating. In its simplest form, fasting aids weight loss by reducing overall calorie intake. However, scientific research consistently reveals that the benefits of fasting extend far beyond mere weight management, showcasing its remarkable impact on various aspects of health.

Using fasting just for weight management is akin to limiting your smartphone usage to texting alone. Much like your iPhone, which boasts a myriad of functionalities beyond texting, fasting holds a spectrum of health benefits that extends well beyond weight management. Because of many recent discussions related to the science, impact, and interest of fasting, I decided to give you an illustration of what [science says] fasting does to your body. *I do not recommend prolonged fasting for women who are pregnant or actively trying to conceive. If you are thinking about getting pregnant, fasting is a great way to kickstart a healthy fertility journey but should not be employed while actively attempting to conceive (it's not dangerous but it may interfere with hormone regulation specific to reproduction). 

Here’s a look at what fasting looks like in your body over 3 days.

Hours 0-4

The initial four hours following a meal constitute the anabolic phase, a period associated with growth, specifically the constructive process through which the body builds tissue, particularly muscle. During this interval, the nutrients derived from your food are being transformed into tissue growth. Simultaneously, your pancreas releases insulin, facilitating the efficient transfer of glucose from the bloodstream into cells for both immediate energy use and storage.

It's noteworthy that if you happen to be following a low-carbohydrate diet (although we don't necessarily advocate for it), your body predominantly engages in converting dietary fat into ketones, serving as a cellular energy substrate.

Hours 4-16

The subsequent 12 hours mark the catabolic phase, during which your body taps into your body’s energy reserves. It transitions to breaking down larger molecules of stored energy, specifically fat and protein, into smaller energy molecules. These molecules are then mobilized to provide fuel for your cells.

As carbohydrate energy sources are depleted, your body enters a fat-burning state, commonly referred to as ketosis. The absence of readily available glucose prompts the release of free fatty acids from triacylglycerides (fat cells), resulting in the production of ketone bodies. These ketones serve as a sustainable energy source throughout the body.

Concurrently, during this timeframe, autophagy initiates—a vital process facilitating cellular repair and renewal. Autophagy operates by clearing out defective proteins and damaged cellular organelles. Fasting emerges as a crucial regulator of autophagy, as disruptions in this process can lead to issues associated with abnormal cell growth, including conditions such as diabetes, cancer, as well as infectious and neurological diseases. 

Hours 16-24

This phase represents your predominant fat-burning and autophagic state. At this juncture, the majority of your body has exhausted energy from digested food, depleting muscle and liver glycogen. As a result, you're largely functioning within the realm of ketosis. Concurrently, AMP-activated protein kinase becomes a key player, initiating lipid oxidation and gene expression that further supports and enhances the process of autophagy.

Around the 24-hour mark, Human Growth Hormone (HGH) levels begin to rise, ushering in a host of benefits such as improved metabolic efficiencies, heightened cognition and memory, muscle maintenance, and more. This hormonal surge during extended fasting plays a pivotal role in optimizing various aspects of your body's functionality.

Hours 24-72

This marks your "clean burning" state, where your body operates efficiently in ketosis, and autophagy reaches its zenith. During this phase, your body actively transforms fat cells into ketone esters, serving as a potent fuel for the mitochondria in nearly every cell.

Simultaneously, you'll experience a noteworthy enhancement in cognition and mental clarity, thanks to the protein Brain-Derived Neurotrophic Factor (BDNF). BDNF plays a crucial role in regulating, growing, and maintaining neurons. It's worth noting that low levels of BDNF are associated with conditions such as depression, anxiety, and neurodegenerative diseases. This surge in BDNF during this fasting state contributes not only to physical well-being but also to the sharpness and resilience of the mind.

Hour 72+ (yes, you can survive for three days without food)

Congratulations, you've officially entered the realm of a prolonged fast where ketosis, autophagy, and the cognitive powerhouse BDNF are firing on all cylinders, ensuring optimal efficiency. But that's not all—there's an intriguing addition to the fasting repertoire. 

Your body kicks into gear by initiating stem cell production. As insulin-like growth factor 1 (IGF-1) hepatic production decreases, your bone marrow steps up, actively generating new stem cells. So, in addition to being in a fat-burning state, you're also actively participating in neuroprotective and anti-aging protocols for your body. This multifaceted impact underscores the remarkable depth of benefits that unfold during a prolonged fast, reaching beyond mere weight management into the realms of cellular rejuvenation and long-term well-being. 

Fasting unveils a tapestry of benefits that extends far beyond the conventional notions of simply eating less and shedding weight. Beyond the realm of calorie deficits, fasting orchestrates a symphony of metabolic intricacies, from optimizing cellular function through autophagy to tapping into the neuroprotective and anti-aging potentials triggered by BDNF and stem cell production.

Fasting emerges not just as a tool for weight management but as a holistic approach to well-being, offering a pathway to enhanced cognition, improved metabolic efficiencies, and a profound impact on cellular repair and renewal. It's a journey that goes beyond the scale, encompassing a profound understanding of the body's innate mechanisms for resilience, rejuvenation, and longevity. Embracing the broader spectrum of fasting's capabilities allows us to unlock a comprehensive strategy for sustained health, making it clear that the benefits of fasting are, indeed, far more substantial than merely eating less and losing weight.

If you’re looking for a way to supercharge your health and kick off the new year with a clean slate, I recommend trying a water fast. You don’t need to jump into the deep end right away; start with a 6-12 hour fast and go from there.

I will be conducting my very first 72+ hour water fast personally, starting December 12. I invite you to participate or follow along my journey on Instagram @optimom_nutrition.

By Alek Dinesen, MS, RDN, CSCS, PN1
Fertility, Prenatal, & Postpartum Dietitian

Disclaimer: The information provided in this blog is for informational purposes only and should not be considered as medical advice. Always consult with qualified healthcare professionals before making any significant dietary changes or starting any supplements, especially during pregnancy and postpartum.