What It Is
Fasting is simply the voluntary abstention from food (and sometimes drink) for a set period. While it has historical roots in religious and cultural practices, fasting is increasingly recognized for its health benefits. Intermittent fasting (IF), time-restricted eating, and extended fasting are popular forms that vary in duration and frequency.
Fasting triggers the body's adaptive processes, shifting from using glucose as the primary energy source to breaking down stored fats through ketosis. This metabolic shift supports cellular repair, reduces inflammation, and can improve overall metabolic health. Fasting also activates autophagy, the body's natural recycling process that clears out damaged cells and promotes cellular renewal.
We evolved to thrive in periods of both feast and famine. If you cannot fast then it is likely a sign of metabolic dysfunction.
What It Is
Fasting is the voluntary abstention from food (and sometimes drink) for a specific period. While it has historical roots in religious and cultural practices, fasting has gained widespread recognition for its health benefits. Intermittent fasting (IF), time-restricted eating, and extended fasting are popular forms, varying in duration and frequency.
The average person eats about 6 times per day¹, often eating right before going to bed and as soon as they wake up with little time spent not eating (i.e. fasting). This pattern is a stark contrast to the feast-or-famine cycles our ancestors evolved with. Modern eating habits leave little room for the metabolic benefits of fasting, such as cellular repair and fat burning.
Fasting triggers adaptive processes in the body, including the transition from using glucose as the primary energy source to breaking down stored fats through ketosis. This metabolic shift promotes cellular repair, reduces inflammation, and improves metabolic health. It also activates autophagy, the body’s natural recycling system, which clears out damaged cells and supports cellular renewal.
What If I Can’t Fast?
Difficulty fasting could signal metabolic dysfunction or an over-reliance on quick, carbohydrate-based energy sources. People with metabolic inflexibility—an impaired ability to switch between burning carbs and fats—may struggle to fast because their bodies are not adapted to use stored fat for energy. Other contributing factors include insulin resistance, poor diet quality, chronic inflammation, or hormonal imbalances. The good news is that you can always become more metabolically flexible. That’s a post for another time though.
What the Science Says
Improved Metabolic Health: Studies show that intermittent fasting can lower insulin levels, stabilize blood sugar, and improve insulin sensitivity, reducing the risk of type 2 diabetes.²
Weight Loss and Fat Burning: Fasting encourages fat loss by depleting glycogen stores and transitioning the body to burn fat for energy.³
Reduced Inflammation: Fasting suppresses inflammatory markers like C-reactive protein, potentially lowering the risk of chronic diseases.⁴
Enhanced Longevity: Animal studies suggest that fasting may extend lifespan by improving mitochondrial function and reducing oxidative stress.⁵
Brain Health: Fasting increases brain-derived neurotrophic factor (BDNF), which supports cognitive function and protects against neurodegenerative diseases.⁶
Practical Fasting Protocols
Intermittent Fasting (16:8): Fast for 16 hours and eat within an 8-hour window (ex.: just skip breakfast and eat between noon and 8 PM).
5:2 Method: Eat normally for five days a week and restrict calories to 500-600 for two non-consecutive days.
Alternate-Day Fasting: Alternate between eating normally and consuming minimal calories (~500) every other day.
Extended Fasting (24-72 Hours): Involves prolonged fasting but requires medical supervision for safety. I do this every 1-2 weeks by skipping breakfast and lunch one day.
Tips for Fasting Success
Stay Hydrated: Drink water, herbal tea, or black coffee to help with hydration and suppress hunger.
Start Gradually: Begin with shorter fasts and gradually increase duration as your body adapts.
Choose Nutrient-Dense Foods: Break your fast with whole, nutrient-rich meals to replenish essential nutrients.
Ways to Manage Hunger: My 3 favorite ways to curb hunger are…
Chewing gum (PUR Gum is an aspartame-free one I use)
Drinking seltzer water (or water with electrolytes)
Going for a walk
Monitor Your Body: Track how you feel, and consult a healthcare provider before attempting prolonged fasts, especially if you have underlying conditions.
Who shouldn’t fast? Fasting is not suitable for everyone. Pregnant or breastfeeding women, individuals with eating disorders, and those with certain medical conditions should avoid fasting or seek medical advice. Over-fasting can lead to nutrient deficiencies, fatigue, or hormonal imbalances.
Live well,
Brian
References
Bailey, R. L., Leidy, H. J., Mattes, R. D., Heymsfield, S. B., Boushey, C. J., Ahluwalia, N., Cowan, A. E., Pannucci, T., Moshfegh, A. J., Goldman, J. D., Rhodes, D. G., Stoody, E. E., de Jesus, J., & Casavale, K. O. (2022). Frequency of Eating in the US Population: A Narrative Review of the 2020 Dietary Guidelines Advisory Committee Report. Current Developments in Nutrition, 6(9).
Sutton, E. F., et al. (2018). "Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even Without Weight Loss in Men With Prediabetes." Cell Metabolism.
Anton, S. D., et al. (2018). "Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting." Obesity.
Longo, V. D., & Panda, S. (2016). "Fasting, Circadian Rhythms, and Time-Restricted Feeding in Healthy Lifespan." Cell Metabolism.Madeo, F., et al. (2019). "Fasting-Mimicking Diets Promote Autophagy and Longevity." Nature Metabolism.
Mattson, M. P., et al. (2018). "Fasting: Molecular Mechanisms and Clinical Applications." Cell Metabolism.