The concept of fasting seems extreme and obsessive, often associated with eating diseases like anorexia. But the science says that non-obsessive fasting is not only healthy for most, but mechanisms found in our DNA show in essence, we are designed to fast. Not only humans, but most animals.
What happens when an animal fasts? Three distinct phases:
1) in 24 hours, glucose which fuels the body's energy is depletedObviously, phase 2 burning of fat is different for different individuals. It has been calculated theoretically, that an average healthy human can fast for weeks without danger, not that I would recommend it. Penguins, for example can burn fat for 100 days without eating. During this time, energy was measured to have come from mostly fat: 96%, and only 6% from the body's protein... suggesting the body innately protects protein, what muscles are made of. Similar results were found in rats.
2) then protein and fats are used for energy, mostly fat
3) when 80% of the existing fat is depleted, the protein is used which begins to weaken the musculature, damaging the body.
I've often thought that the body can be 'trained' to more effectively burn fat by calorie restriction. In other words, the more you do it, the easier it is to get into that fat burning mode.
How is fasting healthy?
1) Genetic studies of human liver, heart, and muscle tissue were studied by a team led by USC researchers that found that fasting can and does quickly and radically alter gene expression (gene traits). When human cells are cut off from glucose and nutrients for just 1 to 2 days, they function differently, they enter a 'protective mode' ... a standby mode that appears to have been genetically imprinted on body mechanisms for millions of years. A reflexive way that humans and apparently most animals have evolved as a method for dealing with periods of starvation. When in 'protective mode' cells become more resistant to disease.
So, in essence, the body is far better equipped to handle routine fasting as opposed to continuous eating. This is illustrated by what I thought was the most compelling quote of the documentary:
"From the perspective of evolution, it is likely that survival normally involved periods of fasting. The situation we have today, with regular meals and a well stocked fridge, is a historical anomaly. So, it's not surprising that the body encounters difficulties when it doesn't fast and eats constantly. Our genetic heritage appears to be less adapted to this situation than it is to fasting."Invoking through fasting this so-called 'protective mode,' is now being used by some to treat cancer patients under going chemotherapy.
--Dr. Andreas Michalsen, German researcher
2) Also, calorie restrictive diets have been shown to extend life span of nearly every animal, from the amoeba to the mammal. Study after study has proven this. Most recently, a new study shows five days of hunger a month may reduce risk factors for aging and age-related diseases.
So, as I routinely do 24 hour fasts, in essence, eating one meal a day, may not be all that bad for me. As I look for advantage in strength to weight ratio as an athlete, a few less pounds can help.
So, the science seems to show that hungry = healthy. I call this, "food for thought."