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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.


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.

  • Loved your story and would like to try this, although $300 seems a little expensive. I wonder if you can make up your diet instead, and not use theirs? Also, are there limits as to how many times you can do this in one month, can you do it for longer than 5 days?

    • You can absolutely make your own food for this. Longo’s book is available for free at the ProLon website and inside it tells you how to structure your menu. I think the most they would recommend is once per month.

  • I am currently on my third round of Prolon and I have been very happy with it. I did not do it for weight loss as I know any 5 day program is not going to produce a long term weight loss, but I did lose 5 lbs each time. My stomach was flat and my waist was definitely reduced. It made me more aware of portion sizes and food choices. The second time I was more careful afterwards to watch these and I only gained a couple of pounds back and maintained after that. My energy level was good throughout the fast and I was able to do yoga, weightlifting and cardio with no problem.

    I have had stomach issues for several years. Giving my digestion a rest seemed like a good idea and it definitely did calm things down…I felt much better during and after the fast! My cholesterol has always been borderline high, but my doctor was never concerned about it because my HDL was high and my triglycerides were low. After my second round of Prolon I had my annual exam and my cholesterol dropped 42 POINTS! That is a significant drop after about 10 years at around 240, my cholesterol went to 198 and my triglycerides dropped from 100 to 50. My CRP, which has been high for a couple years, also improved.

    Although all of the food overall is pretty tasty (most comes from Italy) my only complaint is that the soups are very bland and literally every one tastes almost the same. I am a Texas girl and I need some kick to my food! I took some creative license adding spices, lemon juice, and a few organic tomatoes to make it taste better and it obviously did not affect my outcome. I will keep doing Prolon a few times a year, followed by a healthy, whole foods diet, until my CRP is in the normal range.

    Thank you for sharing your experience. Some of comments here confirms the old saying that: You cannot fix stupid.

    Some have suggested: why not use Low Calorie or Water Fasting, and save money ?!!!..Obviously, if such approach works for some people, then they don’t need anything. Why not use the Water Fasting Diet that is simpler and cheaper than the Fasting Mimicking Diet ? The response is already provided by Dr. Longo in that the Water Fasting Diet works great under clinical supervision. But the problem is when people do it on thier own, they may decide to improvise and make it ineffective or end up in trouble. Otherwise, Dr. Longo raised no objections to Water Fasting.

    I have tried FMD, and it works great. I lost few pounds, but most important, as you suggested, it gets you into eating less and watching everything you eat. My wife is a nephrologist, and she highly recommends FMD over endless drug use promoted by the pharmaceutical companies. What most people don’t understand is that the purpose of FMD is not just losing few pounds, but allowing the body to heal itself.

    Some comments reflects confusion as to: why the Water Fasting Diet is not simpler and better than the Fasting Mimicking Diet ? The response is already provided by Dr. Longo that the Water Fasting Diet works great under clinical supervision. But the problem is when people do it on thier own, they may decide to improvise and make it ineffective or end up in trouble. Otherwise, Dr. Longo raised no objections to Water Fasting.

  • Seriously? This is basically a calorie restricted, vegan, whole-food ketogenesis start-up. I guess I am missing something with the absolutely absurd cost.

    As Alison Godlewski wrote, you can do this yourself at a fraction of the cost. You also have no need of blood tests, just get your self a Keyto ( and go for the soup, nuts and olives.

    • Not even close to keto. Way too high on the carbs.

      I’m on day 2. My blood sugar before lunch was 104. Thirty-five minutes later it was 168. My blood sugar before dinner was 111. Thirty minutes later it was 167. This is very concerning.

      I am NOT weighing myself daily, but i expect to get to the morning of day 6 and find i’ve not lost a single pound. This was recommended to me for medical reasons, but i want to lose weight, too. I’m not at all impressed so far, but i plan to push through (since i spent so much on it) and see the results.

  • We have a weight loss clinic. We use Prolon diet and/or intermittent fasting for hundreds of our patients. Prolon is an extended version of intermittent fasting to modify IGF-1, which makes all the difference. I have put myself on Prolon, it works great. I lost my abdominal fat and my hypothyroidism went away after three cycles of Prolon.
    Naras Bhat, MD

  • Seems like a great way to get started, but why are none of the ingredients organic??!!! I would do this in a heartbeat if I felt good about the quality of the ingredients. But I don’t want to put conventionally grown food in my body, ESPECIALLY when I’m on a fast trying to detox. Why put toxins in right when your body is trying to get toxins out? Note: the tea is organic. That’s it.

    • There’s not really enough food to be worried about the quality of ingredients. In the entire 5 days, you have less than 20 tiny olives, literally a handful of crackers, and the soups are incredibly small portions, made with VERY few vegetables. The crisped rice, nuts, and coconut that comprise the snack bars are also very small quantities, overall.

      I keep an all-organic, ‘clean food’ kitchen at home, so these things are important to me. Yet I decided not to stress, overreact, or be a control freak about the “ingredient quality” of Prolon, because it’s really not about that. It’s about giving your body a rest on a deep cellular level, and resetting some key biomarkers. It’s very effective, and I knew I wasn’t going to die from ingesting small quantities of non-organic food for five days.

      I’m now on my third round, but this time I’m making my own food and improvising a FMD. The relative tastiness of the food was a pleasant surprise on the first round, but I found the Prolon soups to be disgusting and literally inedible by the end of my second box — my final day’s dinner remained uneaten (even though I was starving!) because I just couldn’t choke down that thick, gloppy mess. I also never ate the kale crackers because they were gross to me, but my husband loved them. I recommend doing a couple rounds of Prolon, and then you’ll have the experience to create your own fast mimicking diet with ingredients that meet your specifications.

  • I tried this diet and liked it. But I don’t like the cost, of course, and can’t believe that 50 companies contribute to the ingredients. It’s just envelopes of soup and some olives and nut bars. I think I can do it on my own by just reading the ingredients on the soup envelopes. However, yes it is convenient and even sort of fun to have little vegan k-ration boxes every day.

  • I tried this diet at the recommendation of my physician. It wasn’t hard- except on my stomach. I really can’t eat certain polysaccharides, and the foods in this diet have inulin and glycerol (the energy drink), neither of which I could tolerate. I substituted plain walnuts for the nut bars and went without the energy drink. Even the soups had inulin, so my stomach hurt most of the day everyday. I think I will try a 5-day fast again, just not this particular fasting-mimic diet. I lost 6.5 lbs on this diet, or my version of it. Not bad for 5 days!

    • I also don’t do well at all with polysaccharides and it was clear this wasn’t right for me. I’m surprised someone else with this type of sensitivity knows about it. I am interested in the science behind this diet. I’m all for fasting and modified fasting. I find the idea that one should have clinical supervision for a five day water fast to be laughable. I’m sure one could get in as much trouble with clinical supervision as without.

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