This article is intended solely for informational purposes. It is not meant to be taken as, and should not be construed, as medical advice. Any changes to your lifestyle or diet should be done in consultation with your doctor or health care professional.

Key points:

  • Fasting Mimicking Diets  (FMDs) are temporary.
  • They don’t have enough nutrients to support life or health long-range.
  • No one should try living on one for more than a few days. You’d starve to death if you tried eating one permanently. But they can have profound benefits if done occasionally.

Every now and then I like to do a three-to-five day fast or a fasting-mimicking diet (FMD).  I’m currently doing one once a month. After trying a number of versions, including the one developed by Dr. Valter Longo and doing some experimenting, I came up with a version of my own which works for me.

I do FMDs partly for weight control. I’m 5′ 11″, 170 pounds, so I’m about the right weight for my height. But now and then my weight starts creeping up a little. When that happens, doing an FMD can help reset it. (Doing Alternate Day Fasting also works well for me when I want a quick reset.)

But the main reason I do FMDs is for autophagy and apoptosis, and because of evidence that both fasting and fasting mimicking diets may contribute to a longer lifespan and healthspan by lowering our mTOR, raising our NAD levels, and clearing senescent cells out of the body and replacing them with new stem cells. FMDs also increase growth hormone in a healthy way while decreasing IGF-1.

Prolon’s Fasting Mimicking Diet

The FMD developed by Dr. Longo and marketed by Prolon has the following elements:

  • On Day 1, those following the diet eat 1090 calories, including 27 grams of protein, 68 grams of fat, and 93 grams of carbohydrates.
  • Over the next few days, it goes down to 725 calories, with 16 grams of protein, 35 grams of fat, and 85 grams of carbohydrates per day.

I tried Longo’s version but found it hard to stay on. It’s high in carbs, which (for me) raises blood glucose and insulin, takes me out of ketosis, and leaves me feeling hungry at the end of the day. 

Most Americans eat hundreds of grams of carbohydrates a day, so for them, it would be a reduction. But for those who’ve eliminated wheat and other grains from their diets, it feels like moving in the wrong direction. So I developed a version that keeps me in ketosis while giving me the benefits of autophagy and apoptosis.

My version: 16 grams of protein…

  • On Day 1, I eat 27 grams of protein.
  • On the other days, I eat 16 grams. (The real point of a fasting mimicking diet is to experience both autophagy and apoptosis. Both require that you cut your protein to somewhere in the range of 16 grams per day (or even less).
  • All protein needs to be from plant sources for the duration of the diet –– no meat, eggs, fish, poultry, or dairy. You should also avoid soy, even fermented soy, when doing the diet.

Why low protein matters

  • Autophagy is a kind of deep cleaning of your cells. Your body needs some fuel, so it scavenges your cells for amino acids it can turn into proteins to keep vital bodily functions going. This accumulated debris out of your cells. It’s similar in a way to taking trash out of your house to be disposed of. Autophagy kicks in when we do without protein for a long enough period of time. See related article
  • Apoptosis is programmed cell death –– in this case the deaths of senescent cells. Around two or three days into a fast, there’s evidence that your body runs out of cellular debris, so it starts eating its own cells. This may sound scary, but it’s good, according to Dr. Valter Longo and Dr. Jason Fung, because the ones it starts cannibalizing are dying/decaying senescent cells. It appears to kick in two or three days after the start of autophagy.
  • Eating more than the allowed 16 grams of protein per day shuts down both autophagy and apoptosis.
  • So, count grams and make sure they don’t exceed 16.
  • Remember that plants have protein, too. See related article: “Why 16 Grams of Protein is the Magic Number”
  • NOTE: I’m not a vegan “in real life,” but I am when doing an FMD. This is because methionine, leucine and some other amino acids that are found mainly in animal sources interfere with apoptosis and autophagy. Just as you shouldn’t eat animals during an FMD, you should similarly avoid soy.
  • I should be clear that I am only talking about how much protein I eat (or limit myself to) when fasting (or doing an FMD). No one should try to live on that little protein indefinitely.  If you try living on a fasting mimicking diet permanently, you’d better have your will made out, because you will die.

50 grams or less of net carbs…

  • After doing several FMDs, I’ve concluded that you do not have to rigidly keep it at 20 grams, which some folks setting up ketogenic versions recommend. You’ll get profound benefits even if you eat up to 50 grams of net carbs per day.
  • To measure net carbs, remember to start with the total carbs than subtract the fiber. It’s indigestible so doesn’t count.

… and around 80 grams of fat

  • What makes an FMD and FMD… what makes it effective… is the low protein. This gives you a little leeway to play with the fats and carbohydrates.  For me, it works bets to set my fats at around 80 grams/day.
  • If you want to go vegan (for the duration of the FMD), good fat sources might include avocados; olives; olive oil, avocado oil; fish oil, krill oil, MCT oil and coconut oil. If you like animal fats, you can add some cream and butter (but no milk).
  • Avoid unhealthy and inflammatory fats like soy, safflower and corn oils. Fats like those found in olive oil and avocado oil appear to be ideal. And some saturated fats (like those found in MCT oil, made from coconuts) can also work well. 
  • Don’t deliberately overdose on fat, just eat a little fat when you’re hungry.


  • Some people doing high fat/low carb FMD diets count calories. But many don’t.
  • For those who want to count them, just follow the guidelines of the Prolon diet. Keep calories to around 1050 calorie total on the first day. Keep them to 750 calories a day or less on the remaining days.

Some of my favorites meals on “my” FMD are: 

  • Lentil soup (a cup of lentil soup seasoned with onions, garlic, cherry tomatoes and parsley… add some olive oil and vinegar for healthy fats and flavoring)
  • Avocados (I had a whole avocado for breakfast one day, on my last FMD; I spiced it up with a little sea salt.)
  • Cauliflower rice with mushrooms
  • A big bowl of peas and carrots and mushrooms with lots of butter and salt
  • A big bowl of veggie soup made with broccoli and cauliflower and mushrooms and onions and kale.
  • I’m not crazy about salads, but if you like them, making a big delicious salad from iceberg lettuce (which has almost no protein), olives, avocados, and cherry tomatoes, makes a great FMD meal.
  • You don’t have to limit quantities, just watch the macronutrients, especially protein. Eat lots of vegetables for a few days, and full-fat salad dressings made from healthy oils.

What not to eat

  • I avoid many of my favorite uber-nutritious foods such as sardines, salmon, grass fed ground beef, natto, organ meats, and chicken soup.  I look forward to eating them again at the end of the diet.
  • In fact, I’ll want to eat them at the end of my diet. They’re all high in taurine, a food that you should eat liberally when the FMD is over, because taurine is used in the creation of new stem cells, one of the benefits of an FMD.
  • I of course avoid sugar and fruit.
  • I take most of my usual supplements, but I avoid astragalus and ashwagandha because they interfere with apoptosis. (They’re good to take for general health, but create problems when you’re doing an FMD.)

Are some FMDs bad?

In my opinion, yes. Any so-called FMD that raises your protein above 16 grams is defeating the whole purpose. You’re not “mimicking fasting” if you’re interfering with the processes that water fasting promotes.

Is my version endorsed by Dr. Longo?

No. His version is very specific. The Prolon diet is a medical diet, which can actually be prescribed by a doctor. My version is just what I’ve come up with that works for me.

The calories, vitamins and minerals in my version come out about the same as the ones in the Prolon diet. Like the Prolong diet, the leucine and methionine in this version are very low. My version allows some cream (if you want some in your coffee) and butter; his is totally vegan. But the cream and butter aren’t going to negate the benefits of the diet, so unless you’re a vegan for philosophical reasons, I don’t see any reason to leave them out.

Why not just fast?

I’m a big fan of fasting. When I fast, I drink water, coffee and tea. I may or may not have a little cream in the coffee. But if I even have a trace of what I think might be a cold or other viral infection ––– such as the pandemic that’s been in the news ––– I’ll do an FMD instead. Studies have shown that if you have a bacterial infection, fasting’s usually fine, and can help you heal from it. But if you have a viral infection, fasting can rob your body of the nutrients you need to fight it off. So if you think you may have been exposed to a serious bug, whether it’s the flu or the famous bug from Wuhan, the evidence suggests that a fasting mimicking diet, which is high in nutrients but low in calories, may be a safer way to go.

Continue to part 2