by Nils Osmar. Revised Feb. 4, 2022
Every now and then I like to do either a three-to-five day water fast or fasting-mimicking diet (FMD). I’m currently doing one or the other once every three months. If you’re thinking about trying an FMD, the key things to be aware of are
- Fasting Mimicking Diets are temporary. No one should try living on one for more than a few days.
- You’d starve to death if you tried living on one permanently.
- They don’t have enough nutrients to support life or health longer than a few days.
- But they appear to have profound health benefits if done occasionally.
Why do an FMD?
I do FMDs partly for weight control. I’m somewhere 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.
Dr. Valter Longo’s FMD
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.
I tried the ProLon version but found it hard to stay on it. 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, 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 ProLong diet can feel like you’re moving in the wrong direction. So I developed a version that keeps me in ketosis while giving me the benefits of autophagy and apoptosis.
- On Day 1, I eat 27 grams of protein.
- On days 2 through 5, if I do all five days, I eat 16 grams of protein.
- 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. No protein with even a tiny amount of leucine. So you should also avoid soy, even fermented soy, when doing the diet.
Why Keeping Protein Low 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 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.
- Autophagy kicks in when we do without protein for a long enough period of time. That’s one of the key reasons for keeping it 16 grams or less.
- After a day or two, 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.
- Eating more than 16 grams of protein a day, or eating even a tiny amount of the amino acids leucine or methionine, shuts down both autophagy and apoptosis. So, count grams and make sure they don’t exceed 16.
- Doing an FMD is also a way of going vegan for a few days. I’m not a vegan normally but I am during an FMD. This is because leucine and methionine are found mainly in animal sources.
- So I eat sixteen grams of protein a day once the FMD gets rolling.
- 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.
Regarding calories, like 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.
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.
You will also need to avoid some vegan foods such as lentils, broccoli, soy or peas on an FMD, because they are high in leucine. Soy is very high in leucine; it has almost as much as meat. Rice also has some leucine, though much less than soy, but I usually avoid it.
I avoid sugar and fruit.
I take most of my usual supplements, but I avoid astragalus and ashwagandha, because they “partially repair” senescent cells by fixing their telomeres. This makes it hard for the body to detect that they’re senescent, so they may not be cannibalized during the fast. (They’re good to take when you’re not fasting, but create problems when taken during an FMD.)
Foods that you could eat liberally during an FMD without worrying about leucine include iceberg lettuce. (You’d have to eat about 100 heads of iceberg lettuce to reach a gram of leucine.) Foods like tomatoes and carrots and celery cabbage and cucumbers and pickles and sauerkraut are great; buy a bunch to snack on during the FMD.
Why not just fast?
This is a good question. It’s not really either/or. 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.
So I’m a fan of water fasting. But if I have any kind of a bug — whether it’s a flu, cold or other type of 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, 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. 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?
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 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. 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 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.
- But I can say 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.