“Fasting” — a practice observed for centuries, yet still shrouded in mystery and intrigue. People fast for a myriad of reasons: health, weight management, religious observance, or even as a political statement. But what happens to our bodies during a fast? And what can we learn from the physiological responses to complete calorie restriction?
A groundbreaking study, conducted by researchers from universities across Germany, Denmark, Norway, and the UK, delves deep into the effects of fasting on the human body. By subjecting 12 healthy volunteers to a seven-day water-only fast, the study offers unprecedented insights into the physiological changes that occur during prolonged calorie restriction.
The study recruited 12 volunteers—seven males and five females—with an average age of 28 and a body mass index (BMI) of 25.4. Through daily blood draws, researchers meticulously tracked nearly 3,000 individual proteins to monitor the body’s response to complete fasting.
Key Findings: Navigating the Journey of Fasting
During the Fast
- Participants transitioned from glucose to fat metabolism within 48 to 72 hours, with ketogenesis increasing throughout the fast.
- Notable changes in protein levels occurred, reflecting adaptations to the fasting state, such as heightened hunger signalling and increased protein breakdown.
- Urinary nitrogen levels decreased towards the end of the fast, indicating the body’s shift towards protein preservation as a survival strategy.
After Seven Days of Fasting
- Participants experienced an average weight loss of 5.7 kg, with the majority attributed to lean mass loss.
- Notably, Extracellular Matrix (ECM) proteins protecting the brain’s neurons and synapses were preserved, highlighting the body’s prioritisation of vital functions during fasting.
After Three Days of Refeeding
- Approximately 80% of lost lean mass was regained within 72 hours, demonstrating the body’s remarkable resilience and adaptive capacity.
- Participants also exhibited a slight reduction in body fat percentage, suggesting ongoing metabolic changes post-fasting.
What’s In It For You?
- Distinguishing Complete Fasting from Intermittent Fasting: While intermittent fasting has gained popularity for its purported health benefits, complete fasting entails unique physiological responses. Understanding the nuances of different fasting protocols is essential for informed decision-making regarding dietary interventions.
- Recognising Individual Variability: Despite consistent trends observed at the group level, individual responses to fasting can vary significantly. Factors such as genetic predispositions and metabolic flexibility influence how individuals tolerate and adapt to prolonged calorie restriction.
- Safety and Considerations for Long-Term Health: While a seven-day fast may be deemed safe under controlled conditions, its practical implications for long-term health and sustainability warrant careful consideration. Balancing potential benefits with potential risks is crucial when exploring fasting as a dietary strategy.
As we unravel the complexities of fasting, it’s essential to adopt a holistic perspective on health and well-being. While fasting may offer certain benefits, it is but one component of a comprehensive lifestyle approach. Prioritising nutritious eating, regular physical activity, and adequate rest remains fundamental for promoting optimal health and vitality.
In our journey to exploring the intricacies of fasting and its impact on human physiology, let’s approach it with curiosity, mindfulness, and a commitment to holistic wellness.
References:
Pietzner M, Uluvar B, Kolnes KJ, Jeppesen PB, Frivold SV, Skattebo Ø, et al. Systemic proteome adaptions to 7-day complete caloric restriction in humans. Nat Metab. 2024 Mar 1.
Wilhelmi de Toledo F, Grundler F, Goutzourelas N, Tekos F, Vassi E, Mesnage R, et al. Influence of Long-Term Fasting on Blood Redox Status in Humans. Antioxidants (Basel). 2020 Jun 6;9(6).
Varady KA, Cienfuegos S, Ezpeleta M, Gabel K. Clinical application of intermittent fasting for weight loss: progress and future directions. Nat Rev Endocrinol. 2022 May;18(5):309–21.
Ogłodek E, Pilis Prof W. Is Water-Only Fasting Safe? Glob Adv Health Med. 2021 Aug 5;10:21649561211031178.
