Diverse research from groups all around the world support the idea that calorie restriction increases life span and improves health.
Calorie restriction by as little as thirty percent can increase life span by up to forty percent.
Populations that fast are noted for their good health and longevity. Early studies of the Mediterranean diet touted as one of the healthiest diets to follow, were conducted mostly on populations of Orthodox Christians, who frequently fasted. It is speculated that it was the fasting more than the diet, which accounted for the low incidence of cardiovascular and other degenerative diseases in this population.
Kitavans are another population that fast daily and are noted for their absence of disease.
To date, caloric restriction is the only intervention known to slow the rate of ageing and increase life-span of smaller animal species such as worms, flies and rodents.
Caloric restriction in laboratory animals has unfortunate side effects such as growth retardation and an increased vulnerability to disease. Laboratory studies on rats, however, have shown that regular fasting of less than 24 hours duration delivered similar life extension to rats without caloric restriction, stunting of growth or infection promotion.
Alternate-day fasting typically involving twenty four hour fasts has an excellent record of life extension and disease prevention in animal trials.
There are studies on rhesus monkeys started in 1987 which are not yet complete but they seem to parallel the results of rodent studies and are predictive of increased life-span as a result of calorie restriction.
Caloric restriction improves virtually all indices of cardiovascular health – both lab animals and humans.
In animal models, caloric restriction delays or prevents all types of cancers, kidney disease, diabetes and autoimmune diseases.
It is not clear whether caloric restriction can extend life-span in humans but the Okinawans, which are some of the world’s longest-lived and healthiest people, consume twenty percent fewer calories than mainland Japanese. Death rates for stroke, cancer and heart disease were only 59 percent, 69 percent and 59 percent, respectively, of those for the rest of Japan according to Laurent Cordain in his book, The Paleo Answer.
Fasting intermittently – short fasts lasting less than 24 hours – have shown to reduce blood pressure, improve insulin sensitivity and kidney function and increases resistance to infectious disease and cancer in human studies.
Many of the benefits of fasting appear to be triggered as glycogen stores in the liver become depleted. This is about twelve to sixteen hours into a fast. This suggests that sixteen hours of fasting is sufficiently long to trigger autophagy.
Fasting and Autophagy
Pathogens can either be extracellular – living outside cells – or intracellular – living inside cells. Extracellular pathogens are killed by white blood cells and although white blood cells can and do enter human cells they are not the primary way our bodies kill intracellular pathogens.
Intracellular pathogens are killed through a process known as ‘autophagy’.
Within cells are organelles called ‘lysosomes’ that digest/recycle intracellular junk such as damaged proteins, organelles, bacteria, viruses and other pathogens. This cellular junk is digested into fatty acids, amino acids and sugars, which are then recycled by the cell to manufacture useful proteins.
There is a homeostatic mechanism within cells that keep the levels of fatty acids, amino acids and sugars constant so when there is a high availability (after a meal for example) autophagy is suppressed. When these nutrients become scarce (after fasting) autophagy is activated.
This means that intracellular pathogens are not targeted after a meal but rather during periods of fasting so that they can be turned into sources of intracellular energy.
Autophagy is a sophisticated part of immune function which:
- Recognizes and destroys intracellular pathogens.
- Delivers antimicrobial molecules to pathogens in inaccessible locations.
- Detects the presence of foreign pathogens and generates antibodies against them.
Autophagy is thus a detection as well and a killing mechanism that activated the immune system against infections.
Some pathogens have evolved in such a way that they suppress autophagy as an evolutionary adaptation. These include Herpes Simplex virus type 1, Epstein-Barr virus and cytomegalovirus.
Dysfunctions in autophagy can lead to diseases such as cancer, neurodegenerative diseases, infections and early ageing.
Optimal Fasting Time for Autophagy
In newborn infants, autophagy is turned on within thirty minutes of birth to make up for loss of nourishment from the placenta.
Autophagy peaks at the end of an overnight fast and is at it’s lowest just after breakfast.
As mentioned earlier, glycogen stores are depleted in the liver within twelve to sixteen hours, which would make sixteen hours sufficient to induce autophagy.
What about longer fasts?
In mice trials, autophagy peaks within the first twenty-four hours of a fast and drop back to normal within forty-eight hours of fasting.
Although long fasts do up-regulate autophagy, there is an exaggerated drop in autophagy once regular feeding resumes.
In a study of famine victims who had lost 25 percent of their body weight during a famine and were then given unlimited food found that only 4.9 percent had detectable infections when re-feeding began but 29.1 percent had detectable infections two weeks later.
The infections in the trial group were all intracellular infections, primarily malaria.
Because re-feeding after a fast suppresses autophagy, fasts should be shorter than 24 hours in order to maximize immunity.
Autophagy has also been shown to follow a strong diurnal rhythm so fasting should maintain that as well with a long overnight fast followed by daily feeding.
If Fasting Promotes Longevity then Overfeeding Shortens Life Span
Critically ill patients in hospital bed who experience regular feeding together with no exercise showed a 62 percent reduction in autophagy vacuoles and proteins normally degraded by autophagy. Lack of autophagy was associated with organ failure in these patients.
Athletes that overfeed to gain strength and size exercise and are healthy yet their life spans are shortened by overfeeding. National Football League player have an average age of death of less than sixty years! It is estimated that each years playing in the NFL takes three years off player’s lives and life span is shortest for the largest, strongest men.
There are certain infections where fasting is contra-indicated. Food restriction has been shown to increase the severity of flu, a viral infection with cold-like symptoms. It also appears to accelerate the progression of Amyotropic Lateral Sclerosis.
Fasts should be short, less than twenty-four hours and it’s better to fast frequently but briefly.
If you feel unwell or become very hungry during a fast, eat!