The difference between time-restricted eating (TRE) and intermittent fasting | Satchin Panda
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Integral to the benefits associated with time-restricted eating is the concept of fasting physiology, which taps into ancient patterns of defined periods of eating and resting for the purposes of survival. The consumption, digestion, and metabolism of food produces highly reactive molecules that can damage cellular components, including DNA. Time-restricted eating, however, provides the body a much needed "down time." In this episode, Dr. Satchin Panda explains how time-restricted eating realigns the primordial rhythms of our physiology, allowing us to repair and rejuvenate our bodies.
Rhonda: I think people may be confused by this time-restricted feeding, which is essentially, you know, feeding within our active hours.
[Satchin] Yeah.
Rhonda: The daylight hours, and intermittent fasting. So there's obviously some overlap between the two because if you're, let's say, you're feeding within a 12-hour period. So you wake up, you have your first sip of coffee, that starts your clock. All right. That's it. So, 8:00, then you better stop eating by 8 p.m. Right? That's for 12 hours.
Satchin: Yeah, yeah.
Rhonda: Then from 8 p.m. all the way till 8 a.m. the next morning, you're fasting, right?
Satchin: Yeah, yeah.
Rhonda: You're not getting any energy.
Satchin: Yeah.
Rhonda: So, so in some ways you're getting a lot of...there are some overlap between this time-restricted feeding and intermittent fasting, for example, which has been shown to increase ketone bodies like beta-hydroxybutarate, which I know you've also shown restricted feeding does increase that as well. It takes around, I think, 10 to 12 hours...
Satchin: Yeah.
Rhonda: ...for your liver glycogen to deplete and fatty acids get immobilized, they go to the liver, you start to make beta-hydroxybutyrate and other ketone bodies which then get transported to other tissues and are used for energy in the brain, or they act as signaling molecules.
Satchin: Yeah.
Rhonda: Which Eric Verdin at UCSF published. There's lots of...oh, have...can you, first of all, differentiate for people, like, the difference between intermittent fasting and time-restricted feeding? Like, what are the main differences, and maybe what some of the similarities are?
Satchin: Well, both of these depend on this idea, as the commonality is this prolonged period of fasting. When I say prolonged, that's usually longer than six to eight hours because that's how long it takes for glycogen to deplete or maybe the fatty oxidation to begin so that we begin to use some of the fat. And you also pointed out ketone bodies and beta-hydroxybutyrate, those are also produced maybe after 8 to 10 hours.
So the bottom line is this, that is when we eat we have a type of physiology where we're using glucose and we're driving some bodily function. And at the same time, we may be also damaging some cellular components because of all the reactive oxygen species that we generate during eating, during metabolizing all of this. So all of these have to be repaired, and for some reason, we do not know why, the repair mechanism happens only during the period of fasting. And during this period of fasting, we switch to a different kind of metabolism. Just like you said, our primary energy source is not the readily available glucose from food anymore. It has to come from different sources.
In some cases it can come from a little bit of protein, that's gluconeogenesis or from fat oxidation or, just like you said, ketone bodies. So these things, this physiology, the fasting physiology, we actually know...we are just seeing the tip of the iceberg of fasting physiology. We're just learning about a very few molecules. We don't know what happens to lot of signaling molecules, how the mitochondria actually repair during fasting. Is it actually necessary, to why some repairs happen only during fasting. Why can't they happen when we're eating? So all of these questions are out there but what is common between this intermittent fasting and time-restricted feeding is this fasting physiology that we're beginning to understand.
The reason why we coined and use the word time-restricted feeding is we are not restricting calories, at least in experimental animals. So in that way the intermittent fasting came from calorie restriction, and every other day feeding that had a serious component of caloric restriction that many people thought is difficult to achieve. So that's why we stayed away from the word caloric restriction or fasting, and we used the word feeding because people thought, people may have a positive attitude towards it.
Other than that, I think the idea of fasting is ingrained in evolution. Just like in circadian rhythm, the animals have access to food only during their awake time which can be less than 12 hours, and also for diurnal animals, which are hunter-gatherers, the only time, actually, they have to hunt is twilight time because if you ever go to Savannah, or any of the African countries where there is still wild animals, or if you go to even a zoo, then you know that animals are not active in the middle of the day. They're mostly active during morning and evening. So in nature, animals actually have only two chances to eat, and the rest of the time they're fasting. So this fasting physiology is a very natural response to repair and rejuvenate, and in time-restricted feeding, we're kind of exploiting, or we're kind of bringing back that primordial physiology that's ingrained in our genome, that our genome has to respond to that fasting on a daily basis.
At the same time it syncs with another aspect of the genome; that is it helps us stay awake for 10 to 12 hours and to reduce our energy level and go into a sleep or less active state for the rest of the day. So in that way, it brings back the primordial rhythms in our physiology, metabolism, repair and rejuvenation, whereas intermittent fasting actually helped us to learn various basis for this fasting physiology.
Rhonda: That makes sense.
A chemical produced in the liver via the breakdown of fatty acids. Beta-hydroxybutyrate is a type of ketone body. It can be used to produce energy inside the mitochondria and acts as a signaling molecule that alters gene expression by inhibiting a class of enzymes known as histone deacetylases.
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.
The body’s 24-hour cycles of biological, hormonal, and behavioral patterns. Circadian rhythms modulate a wide array of physiological processes, including the body’s production of hormones that regulate sleep, hunger, metabolism, and others, ultimately influencing body weight, performance, and susceptibility to disease. As much as 80 percent of gene expression in mammals is under circadian control, including genes in the brain, liver, and muscle.[1] Consequently, circadian rhythmicity may have profound implications for human healthspan.
Animals characterized by higher activity during the day and sleeping more at night.
A molecule composed of carboxylic acid with a long hydrocarbon chain that is either saturated or unsaturated. Fatty acids are important components of cell membranes and are key sources of fuel because they yield large quantities of ATP when metabolized. Most cells can use either glucose or fatty acids for this purpose.
A metabolic pathway in which the liver produces glucose from non-carbohydrate substrates including glycogenic amino acids (from protein) and glycerol (from lipids).
A highly branched chain of glucose molecules that serves as a reserve energy form in mammals. Glycogen is stored primarily in the liver and muscles, with smaller amounts stored in the kidneys, brain, and white blood cells. The amount stored is influenced by factors such as physical training, basal metabolic rate (BMR), and eating habits.
A broad term that describes periods of voluntary abstention from food and (non-water) drinks, lasting several hours to days. Depending on the length of the fasting period and a variety of other factors, intermittent fasting may promote certain beneficial metabolic processes, such as the increased production of ketones due to the use of stored fat as an energy source. The phrase “intermittent fasting” may refer to any of the following:
- Time-restricted eating
- Alternate-day fasting
- Periodic fasting (multi-day)
Molecules (often simply called “ketones”) produced by the liver during the breakdown of fatty acids. Ketone production occurs during periods of low food intake (fasting), carbohydrate restrictive diets, starvation, or prolonged intense exercise. There are three types of ketone bodies: acetoacetate, beta-hydroxybutyrate, and acetone. Ketone bodies are readily used as energy by a diverse array of cell types, including neurons.
The thousands of biochemical processes that run all of the various cellular processes that produce energy. Since energy generation is so fundamental to all other processes, in some cases the word metabolism may refer more broadly to the sum of all chemical reactions in the cell.
Tiny organelles inside cells that produce energy in the presence of oxygen. Mitochondria are referred to as the "powerhouses of the cell" because of their role in the production of ATP (adenosine triphosphate). Mitochondria are continuously undergoing a process of self-renewal known as mitophagy in order to repair damage that occurs during their energy-generating activities.
A chemical reaction in which an atom, molecule, or ion loses one or more electrons. Oxidation of biological molecules is associated with oxidative stress, a key driver of many chronic diseases.
A plain characterized by coarse grasses and scattered tree growth, especially on the margins of the tropics where the rainfall is seasonal, as in eastern Africa.
A molecule that allows cells to perceive and correctly respond to their microenvironment, which enables normal cellular function, tissue repair, immunity, cognition, and more. Hormones and neurotransmitters are examples of signaling molecules. There are many types of signaling molecules, however, including cAMP, nitric oxide, estrogen, norepinephrine, and even reactive oxygen species (ROS).
Restricting the timing of food intake to certain hours of the day (typically within an 8- to 12-hour time window that begins with the first food or non-water drink) without an overt attempt to reduce caloric intake. TRE is a type of intermittent fasting. It may trigger some beneficial health effects, such as reduced fat mass, increased lean muscle mass, reduced inflammation, improved heart function with age, increased mitochondrial volume, ketone body production, improved repair processes, and aerobic endurance improvements. Some of these effects still need to be replicated in human trials.
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