Fasting leads to weight loss, slows aging, UF research review finds
GAINESVILLE - North American wolf packs can feast on bison or elk and then go two weeks before the next kill. But the wolves' bodies and brains still perform at high levels as they hunt for their next meal, researchers say.
Humans, too, appear well-adapted to periods of hunger. This is likely a trait evolved from early human hunter-gatherers who, like wolves, alternated between periods of feast and famine.
The answer as to how the body manages this,
To understand why, researchers said, one must look to how the body essentially flips a "metabolic switch" during fasting. This means the body moves from burning glucose, or sugar, for energy to fatty acids and their byproduct, ketones.
During fasting, the body converts fat into fatty acids, which can be absorbed by the blood.
Ketones, he said, are a cleaner source of energy than glucose, protein or carbohydrates, the body's other sources of energy. That is because ketones produce fewer "metabolic disrupters," or molecules that can harm cells.
"This switch can happen after a certain period of time fasting," said
Typically, he said, after eight to 12 hours of fasting, the levels of ketones in the blood significantly increase.
And in that window, the dieter isn't restricted to what they eat. "Of course, we recommend healthy food," Anton said.
The second approach is called alternate-day fasting. In the more common model of this fasting regimen, people limit their meals on one day, usually 500 calories. On the next day, they can eat anything at all. "It can be truly called a feasting day,"
A second version of this fasting method is to eat nothing at all on one day while feasting the next.
In a review of scientific literature,
Three of four time-restricted feeding studies demonstrated significant fat loss.
In most studies, participants did not lose significant lean tissue, which is tissue other than fat that includes the body's organs, muscles and skeleton. An adequate amount of lean tissue, Anton said, is necessary to help maintain good physiological function as people age, among other health benefits.
Other forms of dieting, however, often lead to a reduction in both fat and lean tissue, he said.
"An important takeaway is that we all have the ability to switch our metabolism from glucose to ketone utilization," said