Is it Better to Fast? Or do a Fasting Mimicking Diet?

by Nils Osmar. May 31, 2022

In this article I’ll be focusing on fasting mimicking diets, or FMDs. To be clear, I’m not recommending that anyone do an FMD — what you eat is up to you — but I’ll be talking about why I do them and the results I’ve gotten. Nothing in this video is intended as or should be taken as medical advice.

Every now and then I like to do either a three-to-five day water fast or a fasting-mimicking diet (FMD). I’m currently doing one or the other once every three months.

If you’re thinking about trying an FMD, be aware that:

Fasting Mimicking Diets (FMDs) are temporary. They don’t have enough nutrients to support life or health longer than a few days. You’d starve to death if you tried eating one permanently.
But they appear to have profound health benefits if done occasionally.

I do FMDs partly for weight control. I’m around six feet, 175 pounds, so I’m a reasonably good 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, not eating anything every other day for a couple of weeks, 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 switching on a beneficial enzymatic process called AMPK, activating our PG1alpha genes, raising our NAD levels, clearing senescent cells out of the body, and replacing the cells that the body deleted, with new stem cells at the end of the fast.

FMDs also increase levels of human growth hormone, which was associated in the TRIIM trial with a reversal of epigenetic aging, while decreasing levels of IGF-1, the type of growth hormone which is associated with pro-aging effects.

There’ve been a lot of fasting mimicking diets over the years. The original Ketogenic diet, a medical diet developed over a century ago to treat epilepsy, was a form of fasting mimicking diet.

The FMD developed by Dr. Longo and marketed by Prolon, which has anti-aging benefits, 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.

Why not just do ProLon?

I tried the ProLon version but found it hard to stay on it. I’m used to eating low carb, and by that standard, it’s relatively high in carbohydrates, which 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, the carb count in the ProLon FMD would be a reduction. But for those who are fat-adapted, and have eliminated most or all grains from their diets, the ProLon FMD can feel like you’re moving in the wrong direction. It also contains some foods, including wheat and nuts, that I’m allergic to. And I prefer eating fresh organic foods when possible.

What I do instead

On Day 1, I eat 27 grams of protein.
On days 2 through 5, I eat 16 grams of protein.
The real point of a fasting mimicking diet (for me) 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. No protein with even a tiny amount of leucine. So you should also avoid soy, even fermented soy, when doing the diet.
I also eat 50 grams or less of net carbs. This is a little lower than the ProLon FMD, but not by much. To measure net carbs, remember to start with the total carbs than subtract the fiber. Choose carbs that not too sweet. Things like green salads, cruciferous vegetables, leafy greens and avocados are good choices.
I also eat around 60 grams of fat. I 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. I don’t deliberately overdose on fat, just eat a little fat when I get hungry.
Similar to the ProLon diet, I stay around 1,050 calories on the first day, then go down to 750 calories a day on the remaining days.
One easy version of an FMD which comes pretty close to the parameters of the ProLon diet (though it doesn’t match it exactly) is to just drink two fasting mimicking smoothies a day. See recipe here.

Benefits of Autophagy

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 scavenging cleans accumulated debris out of your cells. It’s similar in a way to taking trash out of your house to be disposed of.
After a day or two of water fasting or being on an FMD, the body movies into a deeper kind of autophagy called apoptosis, a kind of programmed cell death –– in this case the deaths of senescent cells. Apoptosis kicks in when we run out cellular debris. We still need protein, so we start eating our own cells.
This may sound scary, but it’s good, according to Dr. Longo, because the cells it starts cannibalizing are a type of slowly dying/decaying cell called senescent cells. This deeper form of autophagy usually kicks in two or three days after the start of our fast.

What not to eat

I avoid many of my favorite high-nutrition 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.
You also can’t eat some vegan foods such as lentils, broccoli, soy or peas on an FMD, because they are high in leucine.
In fact, I’ll want to eat them at the end of my diet, because they’re 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. If you can’t eat foods high in taurine, you may want to take a taurine supplement at the end of the fast.
I avoid sugar and fruit.
I take some of my usual supplements, but I avoid astragalus and ashwagandha when fasting because of their effect on telomeres. They partially repair telomeres, which may sound like a good thing, but damaged telomeres are the way our bodies identify senescent cella and tag them for removal. So I don’t want to be sending confused signals to my body, particularly during long fasts. (They’re good to take, in my opinion, when you’re not fasting, but create problems when you’re doing an FMD.)

Questions and Answers

Why do a fasting mimicking diet? Why not just fast?

I’m a big fan of water fasting. When I fast, I drink water, coffee and tea, but no drinks with any carbohydrates, calories or protein. If you water fast, it’s a good idea to take some electrolytes along with your water.

But if I have any kind of a bug — whether it’s a flu, cold or other type of viral infection –– 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, the evidence suggests that a fasting mimicking diet, which is high in nutrients but low in calories, may be a safer way to go.

Are some FMDs bad?

There are some online that seem misguided to me. I’ve seen versions that include animal protein (high in leucine, which stops autophagy) – to me these violate the key principles of an FMD. Any so-called FMD that raises your protein above 16 grams is defeating the whole purpose. You may still be getting some benefits because your calories are low, but you’re not “mimicking fasting” if you’re interfering with the processes that water fasting promotes.

Is my version endorsed by Dr. Longo?

Not at all. His version (ProLon) 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 follows some very similar principles and that I know works for me.

Things you can eat on my version include:

AVOCADOS. Due to their high fat, low protein and low carb profile, they work nicely in an FMD. I usually add a little salt for electrolytes. They have 3 grams of protein, 2 grams net carbs, and 23 grams of fat
MUSHROOMS. Mushrooms are great for anti-aging because they’re full of spermidine. They have only 2 grams or protein, 2 grams net carbs, 16 calories, and no fat, in a cup.
PICKLES have almost zero carbs, zero protein, and zero fat. Raw fermented pickles are a great choice during an FMD.
SAUERKRAUT – Sauerkraut has almost zero carb, zero protein, zero fat. Rich in beneficial probiotics.
KIMCHI made from cabbage or radishes. Kimchi has 3 grams of protein, 3 net carbs, and zero grams of fat.
If you want some snacks, you can try munching on things like celery, carrots, cherry tomatoes and cucumbers. Keep a tray of ’em around to munch on.
If you’re not sure if you should include a food, check to see whether it contains any leucine.

Does my version work as well as the ProLon diet?

I suspect that it would. But I have no way to prove it. I don’t have a lab with dozens of animals to test it on, or a trained crew of technicians, or a budget. So, I can’t prove that it does. Neither can anyone else who has created an alternative version.
What I can say is that it works well for me. The low carbs keep me in ketosis, and the 16 grams or less of protein keep me in autophagy. I lose weight and have great energy when on this diet. And my cholesterol and triglycerides are fantastic at the end of it doing my version of the FMD.