ongevity experts like Stanford University neuroscientist Andrew Huberman, physician Peter Attia, and cell biologist Rhonda Patrick have embraced intermittent fasting for good reason: Data suggests it’s helpful for metabolic health and longevity.
Time restricted eating (TRE) may help to improve brain and heart health, lower chronic disease risk (1), reduce inflammation (2), and aid in glucose regulation (3). Some intermittent fasting schedules may also trigger ketosis—a metabolic state in which your body targets fat instead of burning glucose for energy—and autophagy, a cellular salvage, cleaning, and recycling system.
There are as many ways to fast as there are Fast and Furious movies. So which one should you choose? Depends on what you’re trying to achieve.
A 2022 review showed that the main outcome of an 8:16 TRE (eat for 8, fast for 16 hours) protocol was weight loss (4). Twenty-four hour fasts, on the other hand, have been linked to increased human growth hormone levels (5)—some studies suggest growth hormone may help boost memory and increase bone density, but further research is required.
Until research yields more definitive answers around which form of TRE is best, we’ve done the next best thing: gone to the experts to see how top dogs in the longevity sphere tap into fasting’s potential life-extending benefits.
Australian-American biologist David Sinclair, Ph.D. is known for his research on epigenetics and aging. It’s been reported that he’s successfully reversed his biological age by a decade through a strict routine of exercise, stress management and diet—which has included daily fasting.
Sinclair thinks that the temporary discomfort from TRE is one of its most important benefits: “If you are hungry for part of the day or part of the week, your body biologically says, ‘Holy crap, I could run out of food here. I need to build survival mechanisms.’ And so it ends up doing that,” he told Jonathan Fields on the Good Life Project podcast. “One of the ways it does that is through these sirtuin enzymes.”
Sirtuins are metabolism-regulating proteins that may help aid longevity by delaying cell aging, death, and regulating cellular stress response (6).
Instead of squeezing multiple meals into his eating window, Sinclair told The Knowledge Project that he tries to consume one big meal around dinner time. And this meal contains the same number of calories that he would have eaten throughout the day. “I have big dinners because I’m making up for the lack of food during the day,” he said. “I’m eating tons of food that I always wanted, but it’s packed into an hour or two.”
Pro tip: Tweak your timing
If a four-hour eating window feels too narrow, extend it. “You’re an individual, you’ve got a different lifestyle, different tolerance for pain and hunger; you’ve got a different microbiome,” says Sinclair. “These are really important things to take into consideration.”
Peter Attia, M.D., was king of week-long fasts—until he realized that he was losing lean muscle mass. At the end of 2020 he quit multi-day fasts to prioritize muscle preservation, which can be a key to extending healthspan.
“Over a period of about three years, I probably lost about ten pounds of lean mass,” he told celebrity trainer and nutrition influencer Thomas DeLauer. “As much as you might exercise during those periods of fasting, which I tried to, you’re just not going to be able to maintain lean mass.”
These days, Attia prefers shorter, more frequent fasts. It has been reported that he typically fasts for 14-16 hours, then eats in an 8-10 hour window, and that occasionally he’ll restrict his eating for up to 22 hours. He practices this 4-5 days a week which can make it ideal for weekend warriors who aren’t ready to give up late nights out.
Pro tip: Eat enough protein
To build muscle, Attia packs as much protein as possible into his non-fasting window in order to establish an eating pattern that allows him to eat enough to maintain lean mass and long-term activity patterns. “My rule of thumb for any eating pattern is that you must eat enough to maintain lean mass and long-term activity patterns,” Attia told DeLauer.
Protein provides your body with amino acids, which act as the building blocks for lean muscle growth and maintenance (8).
Functional medicine practitioner Mark Hyman, M.D., often adopts a shorter fasting window than Attia or Sinclair. He has blogged that he fasts between dinner and breakfast, usually for 12-14 hours.
Hyman says that when you break your fast (hence breakfast), you must eat well, meaning, “Eat real foods, tons of non-starchy colorful veggies, healthy fats, high-quality protein, etc.—are an amazing compliment to any fasting regime.”
“Give yourself at least 12 hours and then you can kind of push it to 14,” Hyman says. “It’s not hard. If you eat dinner at 6 pm, that’s eating breakfast at 8 am. We’re not talking about something that’s unachievable.”
Pro tip: Don’t snack
“Nobody should be snacking in between meals,” Hyman laments on an episode of The Doctor’s Farmacy. “The worst thing that ever was invented was snacks.”
Not only can snacking pack on additional calories, but even a small handful of chips can prevent you from reaping the benefits from your fasting window by causing blood sugar and insulin levels to rise, which can suppress autophagy (9). If you absolutely can’t go without your favorite salty snack, make sure you eat it within your non-fasting window.
“It’s a whole industry of junk food that’s been pushed on us and somehow we were taught that we need to snack,” says Hyman. “It’s the worst. And I think the two things people can do to dramatically improve their health is to get rid of liquid sugar calories and not snack.”
Cell biologist Rhonda Patrick, Ph.D. told podcaster Tim Ferriss that she practices time-restricted eating.
Animal studies suggest that fasting may offer brain-boosting benefits like increased resistance to stress, improved memory, and reduced risk of neurodegenerative disease (10).
Patrick tweeted, “Time-restricted eating within a 10-hr window & fasting for 14-hrs a day without restricting calories altered the body’s production of proteins consistent with a reduced risk of developing chronic conditions such as cancer, diabetes, and cognitive decline.”
According to research published in 2020, a 14:10 intermittent fasting schedule may help reduce the risk of developing chronic conditions such as cancer, diabetes, and cognitive decline (11). In the study, healthy participants were asked to fast for 14 hours (from dawn to sunset) for 30 consecutive days. At the end of the month-long fasting protocol, participants’ blood serum indicated a plethora of longevity benefits like increased levels of key regulatory proteins with a role in:
- DNA repair
- cytoskeleton remodeling
- immune system and brain health
Plus, researchers found the 30-day fast was associated with a serum proteome—a complete set of proteins—that is protective against cancer. The fast also increased proteins protective against obesity, diabetes, metabolic syndrome, inflammation, Alzheimer’s disease, and several neuropsychiatric disorders.
Pro tip: Don’t drink coffee
Patrick thinks coffee may break your fast—even if you just drink it black.
Some experts think straight up espresso won’t impact ketosis or autophagy. But the amino acids in coffee may interrupt those processes, says Patrick. Fasting deactivates growth pathways like IGF-1 and mTOR, which are activated by amino acids. Once you consume amino acids, she says, those pathways reactivate.
“If you’re limiting your amino acid intake along with your caloric intake and everything else, you’re going to deactivate those pathways,” Patrick says. “That’s essential for the activation of some of the benefits of fasting, including autophagy.”
As part of his longevity-boosting routine, Andrew Huberman, Ph.D., has been intermittent fasting for over a decade, according to a podcast interview with YouTuber Derek Cole. On the Huberman Lab podcast, he frequently discusses the benefits of time-restricted eating and fasting (like aiding weight loss, boosting mental clarity, and improving focus).
“Basically for the last ten years I’ve fasted anywhere from 12 to 16 hours for every 24 hour cycle,” Huberman says.
Although he roughly follows a 16:8 fasting protocol, he believes that the common 8 hour window used in studies isn’t the gold standard.
“The popular 8hr feeding window for intermittent fasting is not the consequence of any systematic comparison of different feeding windows,” Huberman tweeted. “8 hours is the amount of time the graduate student that ran the initial studies was allowed to be in the lab.”
Pro tip: Eat low-carb
“I sort of fast until about noon and then almost always eat a low-carb meal,” he says.
When you eat carbs, your body converts them into glucose—a type of sugar that your body burns for energy (12). If you’re following a keto diet, reintroducing carbs into your diet stops ketosis, which makes your body switch back to burning glucose instead of fat.
Huberman told Derek Cole that he almost always opts for steak or ground beef with Brazil nuts and sometimes vegetables to break his fast.
Cabo, et al (2019). Effects of Intermittent Fasting on Health, Aging, and Disease.
Goldenberg, et al (2022). Role of pulsatile growth hormone (GH) secretion in the regulation of lipolysis in fasting humans.
Grabowska, et al (2017). Sirtuins, a promising target in slowing down the ageing process.
Rahnasto-Rilla, et al (2018). Natural polyphenols as sirtuin 6 modulators.
Carbone, et al (2019). Dietary Protein and Muscle Mass: Translating Science to Application and Health Benefit.
Menikdiwela, et al (2020). Autophagy in metabolic syndrome: breaking the wheel by targeting the renin–angiotensin system.
Gudden, et al (2021). The Effects of Intermittent Fasting on Brain and Cognitive Function.
Mindikoglu, et al (2020). Intermittent fasting from dawn to sunset for 30 consecutive days is associated with anticancer proteomic signature and upregulates key regulatory proteins of glucose and lipid metabolism, circadian clock, DNA repair, cytoskeleton remodeling, immune system and cognitive function in healthy subject.