LOS ANGELES — The box is lovely, sleek and white. But it’s so small.

I’ve decided to try the ProLon diet — five days of “mimicking fasting” that is supposed to help me lose weight, trim belly fat, drop my cholesterol and glucose levels into healthier zones, and even slow aging. I’ve been researching the science behind fasting — check out my full story on that topic here — so I’m excited to try it myself.

But the box is so small. Not much larger than a shoebox, it contains all the food and drink, other than water, that I’ll get for five days. I sift through the futuristic-looking — and tiny — packets of olives and freeze-dried soups, kale chips, and nut bars. I love food so much. I’m a little bit worried.


The diet consists of an ultra-low-calorie blend of proteins, carbohydrates, fats, and nutrients that’s meant to trick the body into thinking it is fasting, but with less discomfort or risk than a true water-only fast. That’s according to its inventor, biochemist Valter Longo, the director of the Longevity Institute at the University of Southern California.

He’s launched a company, L-Nutra, to market the diet; it’s sold for $300 per box or $750 for three boxes, if you’re inclined to repeat the five-day fast every few months. (L-Nutra provided one box to STAT at no cost.)

Fasting, Longo says, pushes the body to burn fat, rejuvenates cells, and lowers risk factors for a host of diseases. I’ve read the scientific studies and there’s ample evidence that fasting can have great benefit for research animals, such as the mice in Longo’s lab.

The evidence for human benefits, though, is more speculative. Short-term studies have shown that fasting can improve certain data points in human subjects (such as lowering cholesterol levels), but there’s no proof yet that such improvements are sustained in the long run — or that they’ll lead to clinical benefits such as fewer heart attacks or longer lives.

There’s also no proof that Longo’s particular blend of foods works any better than any other low-calorie diet or intermittent fasting regime.

So I’m going into this armed with skepticism … but also, a great deal of curiosity. A 40-something mother of two, I’m not technically overweight but a good 15 or 20 pounds over my ideal weight. I want to know what effect the diet will have on my health.

Also, whether I’ll have the willpower to stick with it.


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Most people can choose any five-day period for the diet, so they can avoid big social events or strenuous athletic activities. But I need to diet on five specific days because I’m taking blood tests immediately before and after to gauge how the diet affects my body. (I get the tests done at USC, so Longo can pull the results, but STAT pays for the lab work.) Because of poor planning on my part, the first day of my fast falls on Mother’s Day.

I love food so much. And the box containing my diet for the next week is so small. I’m a little bit worried.

So the one day of the year I normally get breakfast in bed, I get nothing. Which makes me grumpy. I make myself a cup of spearmint tea. My breakfast will be an “L-Bar” — a 280-calorie nut-based bar. Since we’re going on a hike, I decide to wait to eat the bar in case I get hungry while we’re out. It’s not a great start.

I open the bar mid-morning, while hiking. It is delicious. A blend of macadamia nut butter, almond meal, and coconut, it tastes like a dessert. I eat half, slowly, and save the rest for later.

I am getting grumpier. I am also starting to get a bad headache. I think it’s because I haven’t had any caffeine, but USC research nutritionist Mahshid Shelehchi, who is supervising my fast, tells me that it’s normal to get a headache while fasting. Even non-coffee drinkers get them.

Diet plan
Welcome to my lunch: freeze-dried soup, a vitamin, and a handful of olives. Usha Lee McFarling/STAT

Lunch is tomato soup that I microwave, olives, and kale-and-seed crackers with a kick of pepper. It all tastes pretty great. My afternoon snack is another nut bar — I could get used to these, I think — and spearmint lemon tea. Dinner is another freeze-dried soup, minestrone. I deeply resent the 120-calorie soup as I cook it. This is not the Mother’s Day dinner of my dreams. At least I get dessert — a “Choco Crisp Bar” that’s delicious. All four bites of it.

With my headache roaring, I decide to turn in earlier than usual.

I am getting grumpier. I am also starting to get a bad headache.

The first day’s diet contained 1,150 calories. It was hard, but not impossible. Tomorrow I have to drop to 800 calories. I’m not sure I’ll make it.


The 800-calorie days all include a bonus: A glycerol solution you mix with water that serves as an energy drink to help you get through the day. I flavor mine, as advised, with a sachet of hibiscus tea from the box. It’s crazy bright pink but because it staves off hunger, I can tell it is going to become my best friend.

I drink my spearmint tea, trying hard not to look at my cappuccino machine, which seems to beckon me from across my kitchen. Being Californian, I also really want my avocado toast. Instead, I unwrap a nut bar.

Then it’s off to USC, where I have a busy day visiting Longo’s lab. I end up staying a long time so I don’t even get to eat my lunch of mushroom soup and olives until about 3. I feel OK, considering. When I realize I get olives with my afternoon tea also, I’m thrilled. It seems like a bounty.

My entire family is obsessed with my fasting diet — and not all that helpful.

My son asks: “Will you poo?” (Constipation is a side effect; I survived.)

My husband decides to make his childhood favorite meal for dinner — sloppy Joes. While I eat my “Quinoa Mix Soup,” my family raves about how good their sloppy Joes are. “These are so good, they could be served in the finest restaurants of Barcelona,” my husband says. I am sad.

I do get a Choco Crisp Bar for dessert. And I don’t even miss having wine with dinner. I crawl into bed early, with laptop, and start devouring episodes of “Queen of the South.” Thank you, Netflix, for giving me something to binge on.

Usha McFarling
The author (left) and a friend enjoy burgers and pulled pork sandwiches (with fries!) after skiing. None of that would pass muster on the fasting diet. Peter Dickinson


Tuesday is my hungriest day. There is no afternoon snack, no Choco Crisp Bar. Just one nut bar, tomato soup, kale crackers, minestrone soup, and the energy drink, which I carry everywhere like a security blanket.

I need to finish up an article and I feel a little dopey, so I admit to the scientist I’m interviewing that I’m on a fasting diet. She’s intrigued and wants to know all about the biochemistry behind it. Everyone, actually, wants to know about this crazy diet I’m on.


Wednesday, I have a busy day shadowing several groups of elementary school kids for another story I’m writing. It’s a lot of walking, for hours, and I have to occasionally sit and rest in the shade. I wonder if this is what it feels like to be old. Shelehchi advised me that I might not want to drive while fasting, for safety, but between work and my kids’ many activities, that’s just impossible. I do skip my exercise classes.

It’s a lot of walking, and I occasionally have to stop and rest. I wonder if this is what it feels like to be old.

On Wednesday night, my husband has a work dinner that happens to be at my favorite restaurant. (I’m mad and jealous.) So I have to shop and cook for the kids. I’m worried about going into a grocery store while fasting, so I steel myself out in the Trader Joe’s parking lot. I take several gulps of energy drink and walk in the store.

It’s actually not that hard. I look at the food — the shrink-wrapped meats, the frozen pizzas laden with cheese — and it all looks kind of … disgusting. I don’t want to eat any of it.

I could maybe use an extra nut bar, but I’m OK with my soup. And my Choco Crisp Bar.

Diet Plan
I could get used to these nut bars. They taste like dessert. Usha Lee McFarling/STAT

Cooking dinner for my kids is a breeze. I don’t feel hungry anymore. I kind of love having all my meals planned out for me and so easy to prepare. I even feel a little spoiled. Best of all, my headache has disappeared. I thought I would miss normal food and wine with dinner. (No alcohol is allowed on the diet.) But what I miss most, still, is coffee.


Thursday is easy. I have a lot of energy, which Shelehchi says tends to happen after the initial fasting days. She even does her kickboxing classes while she’s on the fast. (Initially unconvinced by the diet, she came around after seeing data from the studies she helps Longo run and now uses the diet several times a year.)

I run some errands and end up staring at a man eating Mexican food out of a styrofoam container. I want to grab his food. Maybe it’s time to return to the world of the eating.

I can’t eat Friday until after my follow-up blood test in the morning, but it’s not food I care most about. I’m plotting how to get my cappuccino as soon as possible after my blood is drawn.

You’d think I would want to binge on food after doing the diet, but the coffee is enough. Which is good, because Longo advises transitioning your stomach back to normal food with soups, juices, and light meals on the first day after the diet.


After the blood draw, I sit and chat with Shelehchi at a coffee shop near the clinic. I’ve lost nearly 4 pounds. I feel great. Shelehchi is not surprised. She says my body is now in ketosis, or fat-burning mode, and I should still keep seeing benefits for several days during “refeeding.”

I kind of love having all my meals planned out for me and so easy to prepare. I even feel a little spoiled.

I tell her one benefit of the diet is that I realize I can eat a lot less food than I do — that right now, much smaller portion sizes and light soups for lunch seem a really easy way to keep losing weight. It’s a common side effect of the diet, she says, adding:  “It makes you think about every single thing you put in your mouth.” She said many women (like me) who carry extra fat they never lost after pregnancy are able to lose it using this diet.

I knew my cholesterol was on the high side going into the diet — I’d recently had a physical and had elevated cholesterol for the first time in my life. My doctor said it was probably due to the high-protein diet I had been trying, and Longo agreed. “It’s the worst idea,” he said. “The absolute worst.”

So, when Longo calls later with my blood test results, I’m delighted to hear that my overall cholesterol and my LDL, or bad, cholesterol dropped during the five days of the diet, though my triglycerides didn’t. I also saw big improvement in my levels of IGF-1, or insulin-like growth factor-1, which is linked to higher rates of cancer. (Longo says mine might have been elevated originally because of that high-protein diet.) It’s not clear if lowering IGF-1 translates into better health or longevity, but it can’t hurt.

I’m a cynical journalist and I’m known to be skeptical — especially about faddish health food claims, heavy marketing, and quick fixes. But this diet seems to have worked for me in the short-term. Nearly one month after ending the diet, I’m still eating much smaller portions, many of them plant-based, and limiting my protein intake. I’ve lost three additional pounds.

And I’m still savoring every cup of coffee.

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  • I found the diet very easy. 3rd day was a bit hard with not much to eat.
    I did cheat a bit, I didn’t give up caffeine but did cut down to one cup of tea with caffeine in the morning.
    Also had a glass of wine a night. Can’t give up everything at once, lol

  • Where can I find the ingredients for each of your packaged foods. I have many food intolerances and want to check ingredients before I purchase the fasting program.

  • I tried the diet for 5 days. Like the author, I found that it wasn’t all that difficult.

    However, rice is a significant component of the food. Given concerns about arsenic in rice, I would not try this diet again until and unless they use something to replace the rice.

  • Dear Usha, To get a better understanding of how we should eat (I don’t strictly follow the keto-diet although I periodically do) read this book… (Seriously!) —“Eat Bacon, Don’t Jog” by Grant Petersen.

    If you want to delve even deeper then read … “Primal Body, Primal Mind” by Nora Gedgaudas.

    Neither Grant or Nora (I don’t know these people) are medical doctors but their books are sourced from endocrinologists and other such experts in the medical field.

    This science is real and the diet is based on the one (basically) that we have evolved on for 2.6 million years.

    Carl Davis

    • We haven’t “evolved on any diet for “2.6 million years”. We would have a hard time describing the diets of 4 thousand years ago. Any “science” from “2.6 million years” ago is not science, but a fairly-tale. In fact, why stop at “2.6 million”? Why not step up your game by using something more impressive like, 6.8 trillion years?

  • I’m contemplating buying this instead of doing a water fast. I found it very painful to eat after 90 hours of fasting die to developing thrush. So I’m thinking this may be a better option.

    • Since you developed thrush, it brings to mind that you may have developed a condition known as candida, which involves high concentration of yeast in the intestines and blood. So going on a water fast diet was a very good proticol for you. I would recommend a 5 day fast every month until the thrush condition does not raise its ugly head when you fast. And if starchy carbs, sugar and dairy compose a great portion of your diet, then it might be proactive to reduce them significantly. Good fasting to you!

  • I talked w a plant-based cardiologist who has been doing this for 5 months now. He says that the cost is high because there are over 50 companies/organizations/entities who contribute to the ingredients in the food provided. And, Dr. Longo does not profit off this. The proceeds go to a non profit organization and back to research in this arena.

    Additionally, it’s not just calories, but rather ratios of the macronutrients that have been researched, so I’m not sure if doing this yourself (grocery shopping and eating foods that equal the same calorie content) would yield the same results. However, it wouldn’t hurt to try- if anything, I imagine it would help you become a more mindful eater after the fasting concludes.

    • When the research paper first came out, I tried the diet using my own smoothie recipe where I tried to reproduce the macronutrients in the study. It was difficult and I really appreciate the ProLon meals. I had DEXA scans before and after the fast and my visceral fat was reduced by 50%.

  • It cracks me up that somebody would pay $300 to fast. All you have to do is not eat. It’s completely free. Wish I had thought to sell fasting people food…Take a multivitamin, keep your electrolytes up with some broth if you have to, but there’s no need to shell out so much money.

    • I completely agree Ashley and what I do. “Eat Bacon, Don’t Jog” explains the science and recipes etc.

  • I agree very high. Where can we order the Box since the first one is free? I feel that if we want to help each other the cost is very high.

    • Tiffany, I think the first box was free for the author of this article so she could do the article on it. I don’t think the rest of us get a free first box. I could be wrong, but that’s what I read. I wonder if those of us who don’t have hundreds to spend could cobble together a similar diet using products found in grocery stores?

    • The reason for no caffeine is because caffeine even sans sugar will spike your blood sugar levels and elevate your cortisol too. Drinking coffee during this quasi-fasting period would make it more difficult to not want to just grab a nice big, fat, juicy cheese burger and chomp! As to the cost being unfathomable to you, well, it’s always about making a buck and for some people that can afford this product they like it because it’s in a way being “done for them”. And for these people who are new to this it can be a short term tool to help transition them into ultimately doing it on their own as they progress.

    • Actually, according to Mayo MD caffeine does not increase or spike blood sugar levels. It may stimulate appetite but I had one or two cups of black coffee on the Prolon diet (with the counselor’s permission) and it didn’t seem to stimulate my appetite–the diet was relatively easy except for day 3–but doable even then. No headache and I lost 4.3 pounds in the 5 days.

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