Caloric restriction vs. periodic fasting and the importance of re-feeding after a fast
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Caloric restriction is a sustained reduced intake of approximately 30 percent fewer calories than one would typically eat, whereas periodic fasting is a more extreme deficit, but only for a short duration. Periodic fasting has distinct phases, unlike caloric restriction: during the acute deficit stage stem cells are activated, and during the refeeding stage, our systems are allowed to regenerate. In this clip, Dr. Valter Longo explains the difference between caloric restriction and periodic fasting and highlights the importance of refeeding after a fast.
Valter: Calorie restriction is, say, 20 percent to 30 percent restriction in calories, so you're basically eating all the time, and you just happen to eat less calories. Fasting and periodic fasting are much more extreme, and we really use them to trick, or manipulate the system, orchestrate a lot of genes to get it to do things like increase protection a lot or turn on stem cells. And so, a lot of these things you can't get by calorie restriction, but you can get them by these more extreme interventions. And, yeah, so calorie restriction also is missing the biggest component of the periodic fasting, which is not fast in itself, but it's refeeding, right? So, most people think of the restriction as what's working, but it turns out, as we've shown in a number of papers, that is the refeeding that is doing most of the work, right? So, they're doing that. For example, when we publish on regeneration, the stem cells are turned on during fasting, but it is the refeeding that causes the rebuilding of the system. And so, the most important part is the refeeding, and in calorie restriction, of course, you never have that. So, it's really interesting how this works, and it's a very coordinated effect based on cycles of fasting and refeeding.
The practice of long-term restriction of dietary intake, typically characterized by a 20 to 50 percent reduction in energy intake below habitual levels. Caloric restriction has been shown to extend lifespan and delay the onset of age-related chronic diseases in a variety of species, including rats, mice, fish, flies, worms, and yeast.
A type of intermittent fasting that exceeds 48 hours. During prolonged periods of fasting, liver glycogen stores are fully depleted. To fuel the brain, the body relies on gluconeogenesis – a metabolic process that produces glucose from ketones, glycerol, and amino acids – to generate approximately 80 grams per day of glucose [1]. Depending on body weight and composition, humans can survive 30 or more days without any food. Prolonged fasting is commonly used in the clinical setting.
[1] Longo, Valter D., and Mark P. Mattson. "Fasting: molecular mechanisms and clinical applications." Cell metabolism 19.2 (2014): 181-192.
A cell that has the potential to develop into different types of cells in the body. Stem cells are undifferentiated, so they cannot do specific functions in the body. Instead, they have the potential to become specialized cells, such as muscle cells, blood cells, and brain cells. As such, they serve as a repair system for the body. Stem cells can divide and renew themselves over a long time. In 2006, scientists reverted somatic cells into stem cells by introducing Oct4, Sox2, Klf4, and cMyc (OSKM), known as Yamanaka factors.[1]
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