By Dr. Frank Sabatino

Programs of calorie restriction and modified eating have become popular for promoting health and weight loss. Some of these programs have often been suggested as routine dietary practices while also being compared and promoted as alternatives to water-only fasting. However, while these approaches provide potential benefits and risks that should be considered, they are significantly different and less effective for detoxification, recovery and healing than prolonged water-only fasting. A discussion of  water-only fasting and intermittent fasting provides useful insight into the benefits and differences of two approaches that are often compared. 

Prolonged Water-Only Fasting

Throughout history and evolution, all species, including humans, have vacillated between periods of food availability  and food deprivation, and have evolved the  ability to adapt to long periods of food restriction and fasting. Water-only fasting is the consumption of nothing but water for an extended period of time and is associated with the following processes and significant health benefits.

When your blood sugar levels drop due to the lack of food intake during fasting, the energy needs of your body are first met by sugar reserves that are depleted within the first 24 hours. After sugar reserves are depleted, the body creates new forms of sugar(energy) from protein (muscle mass) and body fat . 

However, there is no need to worry about the initial loss of body protein. During a fast, there are only a few ounces of protein lost in the first few days of fasting, and only 1/2 – 1 ounce of protein loss per day throughout extended periods of fasting. 

By day 3 of a water fast, your body shifts primarily into fat metabolism, which increases steadily in the subsequent days of fasting. The conversion of fat generates ketones, and the primary ketone, beta-hydroxybutyric acid, produced during fasting provides crucial alternative fuel for the brain and body cells over many weeks of a prolonged fast. In this way, water only fasting is a safe and controlled ketogenic process, as your body feeds on its own fat reserves to satisfy its energy demands.  As a result, fasting promotes the remarkable benefit of decreased risky visceral belly fat that is sustained after the fast especially if you maintain a whole plant-food diet after the fast. During a fast, you can typically lose 1-2 pounds per day. 

Many of the toxic chemicals that are produced by normal metabolism and environmental exposure are stored in fat cells, removed from normal blood circulation, to protect the vital organs of the body. When fat is metabolized for energy during fasting, toxins stored in fat cells will also be released and sent to organs of elimination for removal.  This movement of waste, and subsequent removal by your body, is the process of detoxification. This process is an energy demanding process and one of the reasons why fasting should be done under resting conditions. 

Fasting conserves and harbors energy that would be used for the procuring and digesting food, making it available for cell repair, and detoxification. In addition, your body will direct its blood supply to satisfy the needs at hand. Since you do not need blood supply going to organs of digestion during a water fast, the body’s blood supply is increased to skin and lungs ( your largest organs for detoxification), kidneys etc. to promote increased elimination of toxic debris, often promoting symptoms that manifest this process of detoxification.

Fasting is a condition of complete nutrient deprivation that causes a decrease in insulin and insulin-like growth factor 1, and a decrease in the activity of the cellular enzyme, mTORC1, that normally is involved in protein synthesis and cell growth. As a result, fasting stimulates and enhances the profound process of autophagy (a lysosomal process of “self-digestion”) that shifts the body away from cell growth to maintenance and repair. The process of autophagy destroys and discards damaged parts of cells, recycles beneficial building blocks from cellular debris, and assists in the removal of dead and dying cells that have to be removed and replaced. Fasting also triggers a surge in the compound spermidine, an anti-aging and anti-inflammatory agent, after 36 hours of fasting, that significantly mediates and stimulates the enhanced process of autophagy during the fasting state. (1,2)

Keep in mind that your body knows what belongs in it and what does not. And through enhanced autophagy, it will eliminate what it needs least to support what it needs most. So for example, it needs vital organs like heart, brain, kidney, liver etc. but it does not need tumors, cysts, stones and growths. So in the fasting state, your body will often break down these abnormal growths, recycling from them whatever it can, to feed the organs that are vital to life and health. As a result, water only fasting has been shown to reduce or eliminate cysts in the breast and ovaries, stones in the gall bladder and kidney, and reduce  cancers like lymphoma, as seen in the remarkable research that is ongoing at the True North Health Center. 

Also, the typical lifestyle habits of eating ultra-processed foods and animal products, chronic stress, sleep deficiency and sedentary behavior promote chronic inflammation. that is the foundation of heart disease, diabetes, cancer and stroke that cause the most disability and death, as well as a panorama of auto-immune diseases. Just three to seven days of water fasting can dramatically reduce inflammation and pain in your body, decreasing the production of C-Reactive Protein (CRP) and other chemical messengers (cytokines) that are released by the liver and immune system when your body is inflamed. As a result, water only fasting often promotes dramatic improvement in autoimmune  conditions like rheumatoid arthritis and other diseases of chronic inflammation. (3) Additionally, fasting has been shown to enhance DNA repair, renovate the gut microbiota, and significantly reverse high blood pressure (4) and blood sugar. 

Intermittent Fasting

The use of the term intermittent fasting (IF) is actually a misnomer. True fasting doesn’t begin until the sugar reserves of the body are used up and the body is forced to switch from glucose metabolism to fat metabolism, which takes around 2-3 days of fasting. Even though the body can achieve some ketogenesis and fat loss with IF, IF does not promote the level of food restriction required to enter a sustained fasting state, and is not a true fast. Typically IF programs are really a time-restricted pattern of eating that is useful to align you with the circadian rhythm of your light-dark cycle, urging you to eat in the active light part of your day, and restrict night eating when you should be eating less, winding down and preparing  for sleep. Most often IF is done in the following ways:

(a) A 5/2 day program; eating your normal diet for 5 days and doing 2 days of significant calorie restriction of approximately 500-600 calories per day.(5)

(b) Some form of a time-restricted pattern of eating, where you eat during periods of 4, 6, 8, or 10 hours each day, and you don’t eat during the other 20, 18, 16, or 14 hours respectively. For example, if your first meal of the day is between 10:00-11:00 AM and your last meal of the day is between 5:00-6:00 PM, you are on a 8:16 cycle—eating in a 8-hour window while avoiding food for the other 16 hours.

While this is not a true fast, and does not provide the extensive autophagy andbenefits of longer water-only fasts, there are still major benefits for health and weight loss that can be accomplished with this approach.

A recent review article on the benefits of IF stated that eating in a 6-hour period and fasting for 18 hours can trigger a metabolic switch from glucose-based to ketone-based energy with increased stress resistance, increased longevity and decreased incidence of chronic diseases including cancer and obesity. (6)

While many benefits have been chronicled in animal studies, the suggested human benefits include reductions of abdominal belly fat/obesity, heart rate, blood pressure and inflammation as well as improvements in endurance and cognition. And similar to water fasting, IF promotes some autophagy, DNA repair, and ketogenesis while decreasing insulin and the activity of the aging enzyme mTOR. IF may promote some long-term improvements in insulin sensitivity, gut microbiota, body fat and chronic inflammation thereby increasing resilience and disease resistance. 

Just keep in mind that because you are still eating on a daily basis, the sustained benefits of ketogenesis, detoxification and autophagy that are routinely seen in days to extended weeks of  water fasting cannot even hope to be matched by IF. But for people going through the routine pressures and strains of daily life, and who cannot surrender to the resting demands of water fasting, regular IF can potentially get you back on a healthy track, promote weight regulation, break compulsive eating habits,  and help restore your connection with the normal diurnal rhythms and cycles of your body and the natural world around you.

References

1. Kriebs A. Spermidine controls autophagy during fasting. Nature Aging, 2024, 4:1172.

2. Hofer SJ, et al. A surge in endogenous spermidine is essential for rapamyci-induced autophagy and longevity. Autophagy, 2024 Aug 30;20(12):2824-2826.

3. Kjeldsen-Kragh J, et al. Controlled trial of fasting and one-year vegetarian diet in rheumatoid arthritis. Lancet.  1991; 338(8772):899-902.

4. Goldhamer A, et al. Medically supervised water-only fasting in the treatment of hypertemsion. J manipulative Physiol Ther. 2001; 24(5):335-339.

5. Mosley M, and Spencer M. The Fast Diet: The simple secret of intermittent fasting. Short Books, UK 2013.

6. Castro R, Mattson M. Effects of intermittent fasting on health, aging and disease. N Engl J Med, Dec 16, 2019, 381:2541-51.