Fasting
Human Body, Fasting
Fasting, one of humanity’s oldest therapeutic and spiritual practices, has gained renewed attention in recent decades due to its increasingly well-documented health benefits. Although often associated with calorie restriction, fasting is better understood as a voluntary abstention from food—and in some cases, beverages—for a defined period. This practice influences metabolic pathways, cellular repair mechanisms, and hormonal balance in ways that can meaningfully improve health when used appropriately.
Fasting: Forms, Mechanisms, and Benefits
What Fasting Actually Means
At its core, fasting is a metabolic state. After several hours without eating, insulin levels fall and the body begins shifting from using glucose as the main energy source to mobilizing stored fat.
This shift alters hormone levels, cellular repair processes, and inflammatory pathways.
Fasting should be distinguished from starvation. Fasting is intentional, controlled, and time-limited, whereas starvation is involuntary and prolonged, leading to detrimental consequences.
Popular Intermittent Fasting Protocols
Intermittent fasting (IF) refers to fasting cycles shorter than 24 hours. These are typically practiced daily or several times per week.
16/8 Method (Most Common)
16 hours fasting, 8-hour eating window
Popular due to sustainability and compatibility with daily routines.
Allows gradual adaptation to fasting.
Benefits often include improved insulin sensitivity and easier fat loss support.
18/6 Method
18 hours fasting, 6-hour eating window
Slightly deeper metabolic shift compared to 16/8.
Often used when weight loss stalls or for more pronounced metabolic improvements.
20/4 Method (The “Warrior Diet”)
20 hours fasting, 4-hour eating window
A more advanced form of IF.
Can increase fat oxidation and deepen the fasting benefits due to longer fasting hours.
OMAD – “One Meal a Day” (23/1)
23 hours fasting, 1-hour eating window
A very restrictive protocol that induces a strong fasting response.
Can be effective for appetite control and disciplined caloric intake.
Works best when the single meal is nutrient-dense and balanced.
Extended Fasting
Extended fasting lasts longer than 24 hours and produces more significant physiological changes. These should only be done with proper knowledge, preparation, and ideally medical oversight, especially beyond 48 hours.
24-Hour Fast
Commonly done once or twice per week.
Typical effects observed:
Noticeable insulin reduction
Drop in blood glucose levels
Increase in growth hormone, supporting fat metabolism
Reduction in inflammation and oxidative stress
Initiation of autophagy, the body’s cellular cleaning and repair process
48-Hour Fast
As the fasting window extends beyond 24 hours:
Autophagy activity increases further (some research suggests significantly higher activation compared to shorter fasts).
Insulin and glucose levels remain consistently low.
Inflammation markers tend to decrease more noticeably.
Mental clarity often improves due to stable ketone levels.
72-Hour Fast
At around 72 hours:
Extremely stable low glucose levels
Inflammation drops significantly
Growth hormone peaks, helping preserve muscle tissue
Autophagy is at one of its highest natural levels
However:
Cortisol levels rise during prolonged fasting, especially past the 72-hour mark.
The body begins to worry about energy conservation, which can create stress on muscle tissue.
Protein intake is absent, so muscle preservation relies on hormonal mechanisms (GH, ketones) rather than amino acid supply.
72+ Hours (Prolonged Fasting)
While fasting longer than 72 hours may deepen certain health-related benefits, it also comes with considerations:
Potential benefits:
Strong cellular repair and autophagy stimulation
Continued reduction in inflammation
Ketone levels peak
Maximum digestive “rest”
Considerations/risks:
High cortisol can impact sleep, mood, and muscle tissue
No protein intake means the body may eventually begin breaking down muscle
Electrolyte management becomes crucial
Not ideal for people with high stress loads, low body fat, or high training demands
Dry Fasting (No Food, No Water)
Dry fasting is the most intense form of fasting. It mimics an extreme survival environment.
20 Hours Dry Fasting
This is often considered equivalent to ~24 hours of regular fasting because dehydration accelerates stress and metabolic adaptation.
Up to 24 Hours Dry Fasting
Every hour of dry fasting behaves like 3–4 hours of regular fasting in terms of metabolic stress and autophagy activation.
Why?
No water forces the body to break down damaged cells to extract endogenous water
This accelerates autophagy
Inflammation decreases rapidly
Metabolic rate increases slightly
The body becomes extremely efficient in managing internal resources