Eat differently, live longer? (Part 1)
Researchers are exploring impact of fasting on longevity
The following is informational and not intended as medical advice. While the research reviewed described fasting as a generally safe intervention in most cases, it could pose risks for some people. Anyone considering such a regimen should consult with a physician before changing their diet.
This is part 1 of a 2-part series on calorie restriction through fasting and its impacts on aging. This installment addresses general health effects; part 2 next week will focus specifically on brain health.
In some places – especially around the Internet – the idea of fasting for health benefits, notably weight loss, has become popular. It’s also become a popular topic of nutritional research.
However, fasting is an approach with decidedly mixed reviews about its effectiveness, benefits, and risks. Atlantic.com in 2024 called it “The Fad Diet to End All Fad Diets,” and medical research has documented benefits. But many studies note mixed results, weak associations with benefits, and the need for more research.
The Atlantic’s take may be somewhat overstated. But, while the idea of fasting your way to better health has some merit, it also needs to be considered from all angles before jumping into it.
Pros and cons
One straightforward way fasting can benefit health and longevity is its proven effectiveness as a weight-loss strategy. Obesity is a well-known health and longevity risk because of its association with conditions such as heart disease and diabetes. Fat deposits around the central organs such as the liver and pancreas increase inflammation, another known culprit in the aging process.
Fasting can have some beneficial health impacts beyond just weight loss, however. According to the Cleveland Clinic, these benefits include decreased inflammation and blood triglycerides, along with improvement in blood sugar levels, blood pressure, gut health, immune system strength and sleep quality – all of which are associated with reducing the impacts of aging.
An article from Johns Hopkins Medicine quotes Hopkins researcher Dr. Mark Mattson as saying “Many things happen during intermittent fasting that can protect organs against chronic diseases like type 2 diabetes, heart disease, age-related neurodegenerative disorders, even inflammatory bowel disease and many cancers.”
But it’s not a slam-dunk good. The Cleveland Clinic also warns that “If you’re interested in trying intermittent fasting, you should also be aware of some not-so-pretty side effects. It can be associated with irritability, low energy, persistent hunger, temperature sensitivity, and poor work and activity performance.” (Those Snickers commercials about being “hangry” may have been onto something.)
The Cleveland Clinic and others – including the Mayo Clinic and the University of Michigan – also warn that fasting may not be healthy for anyone who has an eating disorder, is pregnant or nursing, is at high risk of bone loss, or has diabetes. Many older adults are in those last two categories.
Forms of fasting
Fasting diets can take several approaches, including:
Fasting for a set number of hours each day by eating in a certain time window of 8 to 12 hours (e.g., consuming food only between 9 a.m. and 5 p.m.) and fasting the rest of the time.
Alternate-day fasting, which means eating normally on non-fast days, then restricting the number of calories consumed on fast days to around 25 percent of the usual intake.
5:2 plan, which means eating normally on five days of the week but then on the other two days restricting the number of calories consumed to around 500 to 600.
Weekly 24-hour fast: This style involves eating normally six days out of the week but fasting completely during a 24-hour period, consuming only non-caloric liquids such as water or black coffee.
And, of course, such a diet plan doesn’t mean eating with abandon or pigging out on junk calories away from the fast. Food choices during non-fasting times should constitute a healthy, balanced diet with calorie consumption appropriate to age, weight, gender and level of physical activity.
Fasting and the biology of aging
Research into intermittent fasting developed from other research that documented the connections between caloric restrictions and beneficial biological impacts at the cellular level. These include reduced oxidative damage to DNA, better cellular “quality control” through autophagy (removal of damaged cell components), and generation of new mitochondria (which produce the body’s energy at a cellular level). Damaged DNA, lower levels of autophagy and decline in mitochondria all are related to aging at a cellular level.
“A growing body of literature suggests that fasting periods and intermittent fasting regimens can trigger similar biological pathways as caloric restriction,” the editor of Experimental Gerontology wrote in the introduction to a 2013 special issue devoted to the topic, pointing to the prospect of fasting having beneficial cellular impacts.
Another study a few years later reported just such a finding, that “Cells respond to intermittent fasting by engaging in a coordinated adaptive stress response that leads to increased expression of antioxidant defenses, DNA repair, protein quality control, mitochondrial biogenesis and autophagy, and down-regulation of inflammation.” All of those responses help to slow the aging process.
These metabolic benefits start to accrue when the body has depleted its store of glucose, the main energy supply that it gets from food. For most people, blood glucose is used up after about 10 to 12 hours, and something nutritionists call the “metabolic switch” happens. With no glucose to draw on for energy, the body begins metabolizing fat, which leads to a variety of effects at the cellular level including better glucose regulation, increased stress resistance, suppressed inflammation, and enhanced autophagy.
A 2024 meta-review that looked at a wide range of studies said that “intermittent fasting may offer an approach to improve aging-related outcomes” while another study concluded that “The protective molecular mechanisms in cells to survive periods of deprivation of energy resources delay aging and promote (organ) fitness.”
Most of the research documenting these cellular effects were animal studies. Research into the effects of fasting on humans has tended to focus on weight loss. But some research on fasting by humans also reported beneficial findings with respect to aging, such as reduction of blood components that cause inflammation and activation of processes that promote repair of damaged cells.
A recently released book about fasting and anti-aging therapies states the case most bluntly in favor of how fasting benefits longevity:
As intermittent fasting optimizes energy consumption while enhancing cellular processes, such as autophagy, it encourages metabolic health and prolongs life. ... It has been shown that intermittent fasting has the potential to extend lifespans and reduce the incidence of diseases associated with aging by modulating key metabolic pathways.”
Potential benefits, but cautionary notes
So the bottom line appears to be that intermittent fasting has metabolic benefits with some tantalizing links to longevity. That doesn’t mean it’s a fountain of youth — particularly given the concerns expressed by medical professionals from places such as Cleveland Clinic, Johns Hopkins and Mayo Clinic about possible side effects and types of people for whom it might be risky.
These organizations also are unanimous in saying no one should attempt a fasting regimen without getting medical advice. As the Cleveland Clinic puts it: “Your healthcare provider knows your health better than anyone else and can offer the right guidance on whether any of these intermittent fasting options are right for you.”