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LOS ANGELES — He knows he sounds like a snake-oil salesman.

It’s not every day, after all, that a tenured professor at a prestigious university starts peddling a mail-order diet to melt away belly fat, rejuvenate worn-out cells, prevent diseases ranging from diabetes to cancer — and, for good measure, turn back the clock on aging.


But biochemist Valter Longo is convinced that science is on his side.

Longo has spent decades studying aging in yeast cells and lab mice. He now believes he’s developed a diet that may boost longevity — by mimicking the effect of periodic fasting. So he’s packed precise quantities of kale chips, quinoa soup, hibiscus tea, and other custom concoctions into boxes that go for $300 a pop.

Longo’s ProLon diet (it stands for “pro-longevity,” he says, and not “Professor Longo”) reflects a growing interest in episodic fasting, which has been touted by celebrities such as Jimmy Kimmel and Benedict Cumberbatch and in best-selling books like “The Alternate-Day Diet.” His approach stands out because he insists he can use certain combinations of nutrients to trick the body into thinking it’s fasting without actually being on a punishing, water-only diet.

Intrigued, STAT reviewed dozens of scientific studies and talked to a half-dozen aging and nutrition experts about fasting in general and ProLon in particular. We visited Longo’s lab at the University of Southern California’s Longevity Institute, where slender black and white rodents pass their days in clear plastic boxes labeled “DO NOT FEED.” We even tried Longo’s diet for one long and rather hungry week.


Our conclusion? Fasting does appear to boost health — certainly in mice, and preliminary evidence suggests it might do so in humans as well, at least in the short term. It’s not yet clear whether that’s because abstaining from food prompts cellular changes that promote longevity, as some scientists believe — or because it simply puts a brake on the abundant and ceaseless stream of calories we consume to the detriment of our health. Either way, it can be a powerful force.

“We’re not meant to eat three meals a day — and snacks,” said Mark Mattson, a pioneer in studying the effects of intermittent fasting on the brain who runs the neuroscience lab at the National Institute on Aging.

Mice and rats on fasting regimes are slimmer, live longer, and stay smarter and physically stronger as they age. They resist tumors, inflammatory diseases, and the neurodegeneration that characterizes diseases like Parkinson’s and Alzheimer’s. They handily fight off infection and can even sprout new neurons. They don’t end up with diabetes, autoimmune disease, high cholesterol or fatty livers.

Longo, who runs labs at both USC and at at the IFOM cancer institute in Milan, believes he knows why. Fasting, he and others argue, gives cells a break to rest, renew, rebuild themselves and, essentially, take out the trash as the body shifts from storing fat to burning it. They can’t do that when the body is constantly ingesting food, stockpiling excess calories and pushing cells and organs to exhaustion.

“The animal data is very striking,” Mattson said. “These aren’t trivial effects on health.”

Of course, many exciting findings that hold true for lab mice don’t translate to more complex human biology. Small, short-term studies in humans do show that periodic fasting reduces weight, abdominal fat, cholesterol, and blood glucose, as well as proteins like C-reactive protein and IGF-1 that are linked to inflammatory diseases and cancer.

But it’s not clear how long these effects last or whether they translate into any lasting clinical advantage — such as fewer heart attacks or longer lifespan.

So some experts say there just isn’t enough clinical data to prove the diet does everything Longo claims. “These are only animal studies. There isn’t a big body of evidence in humans,” said Kristen Gradney, a dietician in Louisiana and a spokeswoman for the Academy of Nutrition and Dietetics. “It could work, but I can’t confidently say that it will.”

“We’re not meant to eat three meals a day — and snacks.”

Mark Mattson, National Institute on Aging

Yet even some scientists who fully understand the limitations of the data are sold.

Satchidananda Panda, a researcher at the Salk Institute for Biological Studies in La Jolla, Calif., compared mice that were allowed to eat whenever they wanted to mice that only had access to food during a 10- to 12-hour period each day. The differences were profound. The mice that fasted intermittently had no gray fur and weren’t lethargic, even as they neared 2 years of age, the average mouse life span.

The results were so striking, Panda and his family have adopted the practice. He also undertakes a water-only fast for a week each year.

“Once you see these animals,” Panda said, “it’s hard not to follow.”

Mattson, too, eats all of his roughly 1,800 calories per day in a six-hour window in the late afternoon and early evening. He hasn’t eaten breakfast in 40 years.

As for Longo, he uses his own diet every few months — especially to lose weight after returning from stays in Italy. Otherwise, he often eats just two meals a day and is passionate about natural, healthy, and plant-based food.

As one of his senior researchers, Sebastian Brandhorst, put it: “Valter always gives us crap when there’s junk food in the lab.”

Dr. Valter Longo
Longo keeps the mice for his research in plastic bins, some of which are marked “DO NOT FEED.”

‘They thought it was crazy science’

Valter Longo was born to study aging.

Italian by birth, he spent summers in his family’s ancestral home, a town called Molochio in southern Italy that’s home to an unusually high percentage of centenarians. His father is 91. Exactly why the villagers live so long is a question that’s always simmered in the back of Longo’s head.

Now 49, Longo originally came to the U.S. to be a rock star. He enrolled at the University of North Texas, which has an acclaimed jazz guitar program. But he soured on the program when he was forced to run a marching band and turned instead to biochemistry — as a way to study aging.

He moved on to UCLA to pursue a Ph.D. with Dr. Roy Walford, who had become something of a celebrity scientist while pushing the idea that severely restricting caloric intake would extend life.

While he calls Walford a pioneer, Longo soon grew disenchanted with the extreme regimen he espoused. First, it was brutal to maintain. Then, there was what it did physically to Walford, who had been among a Biosphere 2 crew that restricted food intake dramatically during their stay in the experimental habitat. “When they exited Biosphere, they looked liked hell,” Longo said. “Walford looked like a skeleton.”

Walford, a colorful character known for walking across Africa and paying for med school by gaming roulette tables in Reno, Nev., had hoped to live to 120. But he died in 2004 at age 79 of ALS, a disease a number of researchers assert was exacerbated by, or even caused by, his severe diet.

At UCLA, Longo was growing frustrated with Walford’s attempts to study longevity in humans, and even mice, without having adequate tools to drill down into the genetic mechanisms underlying aging. So Longo turned back to biochemistry.

He transferred to a genetics lab focused on yeast, figuring that would let him study the mechanisms of aging in the simplest of organisms.

“If someone said, ‘What are you working on?’ we would say oxidative chemistry. You couldn’t say aging. That was viewed as a joke.”

Valter Longo, University of Southern California

Few people took his early results seriously. Studying aging was still considered flaky. And many scientists at the time were deeply skeptical that you could learn much about human biology by studying simple yeast.

“If someone said, ‘What are you working on?’ we would say oxidative chemistry,” Longo said. “You couldn’t say aging. That was viewed as a joke.”

Convinced his work was important, Longo kept his head down and kept going. “I didn’t pay attention to what people were saying,” he said. In just a year, Longo was able to work out a genetic pathway to describe aging in yeast and show that food — proteins and sugars — could speed aging. It was 1994.

“I was so excited, I thought people were going to say, ‘This is the discovery of the century,’” he recalled. “Of course, it was sent back — rejected.”

Dr. Valter Longo
Research materials in Longo’s lab.

He rewrote the paper and resubmitted. No luck. He couldn’t get any of the work published without taking out every last reference to aging. The discovery he thought most important — the aging pathway — he published only in his UCLA thesis. “We would get insults from reviewers. The yeast world was the worst. They thought it was crazy science,” he said.

As years passed, other groups started publishing work detailing, as Longo had, specific aging pathways, first in worms and eventually in flies. “The frustrating thing is,” Longo said, “we had all of these things figured out and no one was listening.”

Frank Madeo, a yeast researcher at the University of Graz in Austria, had seen Longo being dismissed at conference after academic conference. Now, he said, the work is finally being embraced. “Valter for sure is a fighter. He doesn’t care what others think,” Madeo said. “He did something that at first was considered weird and he was attacked. Now, it’s the basis of work in so many labs.”

The turning point, Longo said, came when an editor at Science recognized that his rejected paper was part of the new paradigm to understand the genetics of aging. The paper was published in 2001, seven years after he’d first submitted it. It has since been cited hundreds of times.

Once he had the aging pathway worked out, Longo went on to look more deeply at what restricting calories did to yeast cells. He found withholding food “completely reprogrammed” the yeast — cells lived longer and were resistant to threat after threat. “You could throw in any toxin you could think of and it wouldn’t die,” he said.

Fasting “is at the foundation of the body’s ability to protect, repair, and rejuvenate itself,” he said. “We started to wonder: What can we use it for?”

So he started experimenting with limiting rodents’ intake of the proteins and sugars that he’d seen activate the aging pathways. (His lab cooks up a diet by hand for the animals; it’s also the inspiration for the the five-day diet he sells for humans.) His team has found that the diet shows promise in restoring pancreatic cells that keep diabetes in check, boosting immune cells, and helping prevent the deterioration of myelin, which plays a role in multiple sclerosis.

San Diego computational biologist Karmel Allison, who blogs at the diabetes lifestyle site ASweetLife, took a deep dive into Longo’s paper on pancreatic cells and found the data unconvincing. She thinks the improvements in mice could have simply come from their weight loss, not from any cellular change brought on by fasting.

Other scientists agree that’s a key question for further study, in both mice and people. A study published in the Journal of the American Medical Association this May startled some diet researchers by showing alternative day fasting was no better at decreasing cardiovascular health risk factors than normal dieting — and was harder to maintain. (Longo maintains that the popular alternate day and 5:2 diets, where people eat up to 800 calories on their so-called fasting days, are not true fasting, just calorie reduction, and therefore don’t cause the metabolic shifts and cellular improvements of his diet. He thinks at least three days of fasting are needed, though other researchers disagree.)

“In humans, is intermittent fasting only effective for weight loss because we’re restricting calories? In my mind, that’s the big question,” said Grant Tinsley, an assistant professor of kinesiology at Texas Tech University who studies sports nutrition. “Is this just about eating fewer calories or are there unique cellular changes?”

“In humans, is intermittent fasting only effective for weight loss because we’re restricting calories? In my mind, that’s the big question.”

Grant Tinsley, Texas Tech University

Tinsley himself practices intermittent fasting: He restricts himself to eating during a six- to nine-hour period each day or does a 24-hour fast once a week. He likes the idea of Longo’s diet. Yet he’d still like more data. “There really are no side-by-side comparisons of different fasting programs in humans,” he said.

He knows firsthand, though, how hard it would be to conduct such a study. For one thing, it’s hard to get corporate funding for a study involving abstaining from food. For another, human beings are prone to cheat on diets. “Obviously it’s not ethical to keep people in cages for a year and feed them what you want,” he said.

Longo can, however, do that with mice. And he and his lab are excited about new studies showing that fasting seems to strengthen normal cells in rodents while making cancer cells more vulnerable. Longo thinks this means fasting may increase the potency of chemotherapy while reducing its side effects.

And, indeed, small clinical trials in humans have shown patients report less fatigue and fewer gastrointestinal symptoms while fasting during chemotherapy treatments. Longo now has clinical trials underway at several cancer centers worldwide to see if his diet improves outcomes as well.

Dr. Valter Longo
Longo has found that mice on fasting diets reap a number of health benefits.

A diet that mimics fasting with beets and cider vinegar

Longo came up with the idea for the fasting mimicking diet about 10 years ago. He was trying to test the effect of a water-only diet for cancer patients. But most patients refused to fast and oncologists were worried about their already thin patients participating.

So Longo decided to devise a diet with minimal calories that would provide the nutrition the patients needed, but also confer the benefits of fasting. His lab worked out the precise amounts and types of calories, carbohydrates, proteins, and fats by testing various diets on mice.

The cancer fasting diet amounts to just 200 to 500 calories a day for four days. The ProLon diet allows 1,100 calories the first day and 800 for the next four. (Longo recommends doing the diet under a doctor’s supervision and notes that it’s not appropriate for people with certain health conditions, such as diabetes.)

His diet is low in protein and fat; he gets furious when he sees doctors advocating the opposite, a trendy practice he believes speeds aging.

He gets really fired up when nutritionists call fasting a fad. “Fasting is as old as it gets,” he said, noting that our hunter-gatherer ancestors likely went long stretches between meals. “If 70 percent of America is obese or overweight, you would think they’d have figured out their [more traditional] interventions don’t work.”

“He said, ‘I need to have something that’s going to have almost no calories but still have taste.’ ”

Ambra DiTonno, cafe owner

To devise fasting diets that people would actually want to eat, Longo turned to Ambra Ditonno, a longtime friend who runs a popular Italian cafe in Hollywood.

The two worked together after hours in Ditonno’s panini shop concocting extremely low-calorie soups — some just 30 to 45 calories per serving — out of pumpkin, beets, tomatoes, and broth. “He said, ‘I need to have something that’s going to have almost no calories but still have taste.’ It was really hard,” Ditonno said.

It’s not typical work for a scientist, but was typical for the hands-on Longo, who’s not married, has no children, and is used to working long hours (though he’s prone to pulling out his guitar when asked, and also does a lot of bike riding).

“He doesn’t have any other interests. He’s married to his job,” Ditonno said. And, she added, he had a natural flair for the work:  “He’s Italian, so he has some idea of cooking.”

They’d then freeze individual portions of the soups for delivery to cancer patients. (The soups are now manufactured in a facility and freeze-dried so they can be easily shipped and stored.) The diets include additional ingredients — algal oil supplements, specific proteins, trendy additions like flax seed, inulin, glycerol, and cider vinegar — that Longo believes act to improve health or trick the body into thinking it is fasting.

After cooking so many fasting soups, Ditonno tried the diet herself last year. She lost weight, got rid of the extra tummy fat she’d carried since having a child and eased several digestive issues. The benefits have persisted long after that initial fasting period. Like many who work with Longo and have tried the diet, she’s become a convert. “I believe in it like 1,000 percent,” Ditonno said.

The idea of a professor marketing his own longevity diet has raised eyebrows. “It’s a tricky spot to be in,” said Allison Dostal, a registered dietitian and Ph.D. from the University of Minnesota. She was part of a watchdog team that wrote a scathing review of a press release touting one of Longo’s studies that was put out by USC, which also stands to profit if the diet is a financial success. “It’s not something I’ve generally seen.”

The cost of ProLon has also raised questions, especially since there’s no proof this particular combination of foods works better than any other ultra-low-calorie diet or episodic fast.

“The diet’s OK,” Mattson said. “I’m just thinking about the people who can’t afford it. A lot of obese people are of low socioeconomic status. That’s the target population that could really benefit most.”

Longo created a company, L-Nutra, to market the diet, and retains majority ownership. He intends to funnel any personal profits into a nonprofit to fund research. For now, not much money is rolling in, though he says about 5,000 people have used ProLon — some paying customers, some research subjects. He hopes to one day receive FDA approval to market the diet as a tool to help prevent diabetes, but that’s well in the future.

Panda, the Salk Institute researcher, calls Longo’s approach a smart business move.

“The general public wants something encapsulated, they want a prescription,” he said. “Valter’s done a very smart thing. He’s encapsulated fasting.”

Correction: A previous version of this story misstated the location of the University of Graz and Allison Dostal’s academic affiliation.

  • At $225 per box, even I cannot afford this and I make a good living. I appreciate his research (though I wish he would not use lab mice) but c’mon now. He has put this out of reach of most people. He drives a Ferrari. He doesn’t need more money, given to him by people who are desperate and dying. I’ll just stick with a plain water, 5-day fast. It’s free and is reversing my diabetes.

  • As a physician, pushing back against big food will become the fight of the next generation as it was against tobacco previously.
    Coca Cola sponsored the World Little League Series. Years ago it would have been tobacco or alcohol sponsoring sports. What’s old is new.

    • I have had a few patients who reduced their pain and inflammation by simply avoiding sugar. Any kind, including low fibre to fructose fruits.
      The pain reduction has been dramatic in many cases. Getting people to buy in, even for 14 days, is a challenge.

  • I do not trust any doctor who has a product to sell other than a book. Dr. Berry, Dr. Peter Attia, and Dr. Fung, all MDs, recommend the ketogenic diet which is high healthy fat, moderate protein, and very low carbohydrates. To here Longo say that fat is bad for humans is ridiculous and harmful. If you want to fast, get into ketosis which makes fasting much easier.

  • Great spirits have always encountered violent opposition from mediocre minds. Albert Einstein himself said it. You keep shining your truth Dr. Longo! I completely believe in and respect everything you have devoted your life to for the past 25 years on this subject. I am very thankful that you are sharing this life-saving information with the world. There will always be nay-sayers, But few have studied this subject as in depth as you have. So just keep shining your light! The world is a better place because of you!

  • Iam 71 years old vet & have lost 103 lbs. In a year. I eat 10 garlic cloves per day. Ive went from 550 units of insolin per day to under 150 per day. My prancras is making insulin. I would sure like to be a test person for your fasting diet program. Please let me know. I think your right on the mark with this againg program. Thank you, Eric.

  • Valter Longo recommends a 12-13 hour fast after night dinner until the next morning’s breakfast.
    For example, if you finish dinner at 8 pm, then fast until 8 am – 9 am the next morning. You
    can drink water during that period.

  • I am a Type 2 diabetic and had very high hopes for this diet, but now I’m a little confused by this article. On one hand the article notes, ” the diet shows promise in restoring pancreatic cells that keep diabetes in check.” and then further down says, “that it’s not appropriate for people with certain health conditions, such as diabetes.” Just wondering what makes it “not appropriate” for diabetics?

    • He is not allowed to tell you it will help. You should involve a professional to properly monitor your results. In my opinion, diabetics would benefit the most from his program, but the FDA says different and he has to play to their rules. Until the FDA decides something is a cure, no one else can claim that without risking their license.

    • Thanks, George. I understand. But perhaps different wording wouldn’t scare away diabetics from trying the program. Such as “has not been fully evaluated to be beneficial to diabetics.” I was completely ready to try it but got spooked when I read that last line. Just my opinion.

    • The sad truth is that big pharma will not cure your diabetes. They give you a drug that hides the symptoms that you take for the rest of your life. If you want to cure it, you need to somewhat take matters into your own hands. Sugar and wheat gave you diabetes. Quit sugar and wheat or take toxic meds till they kill you. Your choice

    • I didn’t mean to make you defensive, George. Let’s get back to the original question. I merely asked what makes ProLon “not appropriate for diabetics?” I really want to give ProLon a try but what should I be careful of while on this program?

    • Oh I am not defensive. It really just boils down to what you want. You dont need Longo’s program (although it wouldn’t hurt), all you have to do is intermittent fast, water fast, and eat healthy clean organic food. That being said I tried to say it in simple truthful terms. Take big pharma’s drugs and get sicker or die – or heal yourself and live. Big pharma’s drugs don’t ‘heal’ anything. They just mask symptoms while the underlying problem gets worse.

    • As far as why you should be careful I answered that in my 2nd sentence of my 1st reply. Because you are a diabetic you should involve a doctor or other health professional to help monitor/interpret your results so that you can do it SAFELY.

    • DIAS,
      You might also Google for Dr. Jason Fung, a nephretologist who has had much success reversing diabetes via fasting and dietary modification to a low carb diet. He has written several books on the topic and explains that a diabetic needs medical supervision/monitoring during the initial phases of fasting and diet change because of the decreasing need for drugs as insulin and glucose return to normal levels. He has published cases where severe diabetics were able to lose weight and completely get off of drugs; they were also still maintaining that status 5 years later. I think Valter Longo and Jason Fung are both heroes! (I’m starting the FMD today)

  • Please read this!
    Water fasting is deadly! There are no real benefits, it is starvation and it can kill you.
    I know. My mom just died as a result from fasting. She was only 57.
    This was her second time water fasting and she had NO medical conditions. In fact, her doctors deemed her unusually healthy for her age. She was active and fit. She had only been fasting for 5 days, shorter than before. She had done her research: read every book and blog, and was taking supplementary electrolytes and minerals.
    Do not believe it when they say there will be warning signs. My mom couldn’t stop talking about how energetic she felt. She was glowing! She was laughing with her friend on the phone: 20 minutes later she was gone.
    Autophagy is only starvation, nothing more.
    Please, if you are fasting: get medical attention immediately. Water fasting can cause heart failure, hyponatremia, seizures, and strokes. It messes with potassium levels, electrolytes, the heart, the brain…and these effects can lie dormant for months, meaning each subsequent fast is deadlier.
    I beg you to think of the consequences…because people like me will be living with those consequences daily.

    • Sounds like a fairy tale to me. According to you every time our ancestors went a few days without food they died….so how did we all get here? Fasting is Natural and safe. You are either lying completely or lying about the cause of her death

    • Don’t trust everything you see on the internet for starters. Remember the supplement ENZYTE that was heavily advertised on tv for a long time? They claimed it would increase the size of the penis! The guy behind the scam got 25 years in prison. Google “a healthy degree of skepticism. If you don’t have it, try to develop it and encourage others to do so too. Good luck Thee end.

    • That doesn’t even make sense. I’ve been on a fast gone wrong. You don’t feel terrific and then 20 minutes later drop dead. My body gave me PLENTY of signs that it was not happy. If she was potassium and sodium deficient she would have felt lousy for a good long while before actually going into an emergency state. Probably for days.

      This post is just a troll, I’m guessing. That or we have a grieving family member who can’t accept that her loved one died for some other reason. Perhaps a stroke or seizure? Those happen out of the blue, and can often be proceeded by a burst of energy and good mood. It’s called a prodrome.

      It just not how fasting works. There are stages to electrolyte imbalance and you have to go through them before getting to an emergency. As long as you don’t ignore what your body is telling you, there’s lots of time to break the fast and recover if things start to go wrong. But you’ll feel it. You’ll know full well that you aren’t feeling well.

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