American scientist and author, Benjamin Franklin, advised, “The best of all medicines is rest and fasting.” Mark Twain’s experience was similar, “A little starvation can really do more for the average sick man than can the best medicines and the best doctors. I do not mean a restricted diet. I mean total abstention from food for one or two days. I speak from experience. Starvation has been my cold and fever doctor for 15 years and has accomplished a cure in all instances.” Jack Goldstein, an American physician, suffering from ulcerative colitis only recovered after observing lengthy fasts of 30 to 40 days once a year for three years.
The ancient Ayurvedic texts equally laud fasting: langhanam param aushadham – fasting is the greatest medicine – and jvarãdau langhanam proctam – at the onset of fever, fast.  In the Ashtanghrudaya,  Vagbhatt Rishi lists the benefits of fasting: “disappearance of aggravated doshas, boosting of the digestive fire, weight reduction, increased vigour and ojas (vitality), digestion of aam (toxins), true hunger and thirst, and the desire to eat.”
Fasting has been a survival mechanism for organisms since the advent of life on earth. During times of drought and food scarcity, organisms enter into a mode of inactivity to conserve energy for survival. Such organisms include single-celled microbes, insects, fish, lizards, bats, squirrels, rodents, bears, crocodiles and even shrubs and trees. Some hibernate during winter, living on stored body fat.
Many mammals also fast during illness or injury, such as dogs, cats, horses and cows. They will avoid even the most delicious food offered to them, taking only water. They resume food only after complete recovery. How do they survive without food? Through a process called autophagy. This word is derived from the Greek auto ‘self’ and phagein ‘to eat’. Thus, autophagy means ‘self-eating’ or ‘self-cannibalization’. The word ‘autophagy’ was coined by a Belgian scientist named Christian de Duve in 1963. In 1974, he won the Nobel Prize in Physiology or Medicine for discovering a cell component known as the lysosome, where autophagy takes place. Autophagy is the process by which cells degrade macromolecules, old cell parts and microorganisms and recycle their components to provide fuel for energy and building blocks for cell renewal. However, the exact mechanism of this process remained unknown. In the 1990s, a Japanese cell biologist, Yoshinori Ohsumi, performing experiments on yeast cells discovered genes essential for autophagy. In 2016, he won the Nobel Prize in Physiology or Medicine for discovering the mechanisms of autophagy.
Why is autophagy important? Because it is the process by which the body cleans out damaged cells and toxins to help regenerate newer, healthier cells. It is also important in counteracting aging. When autophagy goes awry, it leads to aging and many age-related diseases, including cancer. Autophagy is so beneficial that it is now regarded as an important factor in preventing diseases such as cancer, neurodegeneration, cardiomyopathy, diabetes, liver disease, autoimmune diseases and infections.
Autophagy is activated during times of stress, as a way to protect the body. This stress is metabolic stress due to strenuous exercise and food restriction. Activating autophagy slows down the aging process, reduces inflammation and boosts the body’s natural ability to function. Autophagy is important for ‘cleaning up’ the body and defending against the negative effects of such stress.
Since the 1990s, scientists have been hotly pursuing research on animals to discover mechanisms which promote autophagy and drugs which can activate the pathways of autophagy. In a nutshell, this is the science of fasting at the cellular level, since autophagy is enhanced when a person fasts.
Here, it is worth examining the results of experiments on autophagy through fasting in the quest to discover the secrets of health and longevity. Globally, scientists have used various fasting protocols on mice and rats. These include IF – intermittent fasting, TRF – time-restricted feeding, FMDs – fasting mimicking diets and PF – periodic fasting. Their amazing findings have prompted research on humans. A list of conclusions of their results from IF is listed below. IF is similar to the Hindu fasting vrat known as dharna-parna – food one day, fast the next day.

Although the above results in rodents seem amazing, scientists do not (yet) claim that they may all apply equally to humans. Only human trials can reveal this.
In humans, scientists have so far performed trials on one meal a day, similarly to the Hindu fast of ektana during the month of Shravan. Their results reveal reduction of fasting glucose levels, and healthier levels of LDL and HDL cholesterol.
Some research on humans on CR – (caloric restriction) showed improved memory and IF showed increased levels of adiponectin – a hormone which helps to regulate body weight and fat, and also decreases insulin resistance. This induces health benefits and longevity. Studies of centenarians have also shown high levels of adiponectin. 
These findings of science reflect the remarkable benefits to the body and brain of restricting food intake through fasts such as ekadashi, ektana and dharna-parna. Bearing this in mind, Hindus who faithfully observe these vrats will be protected from many diseases and may accrue longevity. As far as the science of fasting is concerned, the benefits can be summed up in the phrase: ‘Eat less, live healthily.’
Next, we discuss the spiritual perspectives of fasting.