01/02/2026
Protein Restriction and Longevity
Protein restriction (PR) is the reduction in dietary protein whilst maintaining normal calorie intake from the other macronutrients. This approach has often been followed by vegetarians and has gained attention in aging research papers for its potential to promote health and extend lifespan.
Studies have used mice, flies, and yeast, and observational data in humans. Pathways involved in cellular growth, repair, and aging have shown a link between PR and either an improvement in cellular growth or an acceleration in aging but - keep on reading it’s a very interesting story.
The way that PR is thought to affect health and longevity is through the mTOR pathway, this includes insulin signalling and longevity mechanisms. I will show you that protein restriction is not the way to optimum health but protein needs to be well managed to get the benefits without the problems. On the other hand insulin, which I have written about many times, can be insidious for your health if kept too high too often.
mTOR
mTOR is a protein kinase that forms two main complexes: mTORC1 and mTORC2. mTORC1 acts as a nutrient sensor and is activated by high protein intake. This promotes cell growth and protein synthesis, but chronic activation is linked to accelerated aging and age-related diseases.
We know that restricting protein suppresses mTORC1 which suppresses muscle growth, but it also triggers beneficial responses like autophagy, which is a cellular “cleanup” process that removes damaged components and recycles the cellular materials. This shift from growth to cellular recycling is thought to delay aging.
Researchers looking at mouse models, found that PR reduces signalling in tumors and all body cells, inhibiting cancer growth and improving health and lifespan. Genetic or pharmacological inhibition of mTORC1 (e.g., with rapamycin) mirrors these effects, extending lifespan in various animal species, but the trouble is lab kept animals are not the same as humans living a normal lifestyle. Also, they are only looking at it through their particular lens, there are many other aspects, some good and bad with PR.
PS. I write more about mTOR near the end of my essay
Amino Acid Specificity: We now know that Leucine, Arginine, and Methionine are the primary "fuel" for mTORC1. Leucine is the most potent activator, found heavily in animal proteins and dairy.
Recent research has shown that while mTORC1 reduction can generally promote longevity, a reduction can also have detrimental effects with longevity which I describe below. Reducing mTORC2 can also cause problems which I also talk about below.
Insulin resistance without lifespan benefits.
Research has clarified that we need to keep both mTORC1 and mTORC2 under control, not too little for muscle strength and growth, and not too much for longevity. mTORC2 handles the structural integrity and survival of the cell, when too low it causes insulin resistance leading to high blood glucose and metabolic dysfunction.
One of my “go too guys” Ben Bikman gives his insight
Ben Bikman PHD is a metabolic scientist, professor and author, best known for his work on insulin resistance, metabolic health, obesity, and type 2 diabetes. Bikman points out that while amino acids (from protein) stimulate mTORC1 which we need for muscle growth, insulin will stimulate it much more potently and for a much longer duration. Protein only causes a temporary "spike" in mTOR which is necessary for building muscle and bone. The real danger is chronically elevated insulin which keeps mTOR turned "on" 24/7 and preventing the body from ever entering a state of autophagy and fat burn.
Bikman argues that research has shown for humans, that muscle mass is one of the strongest predictors of how long you will live. Restricting protein to lower mTOR can lead to sarcopenia (muscle wasting) and frailty especially with the over 65s, which is a greater risk to longevity than mTOR and its activation of insulin.
He argues that animal proteins are superior because they have a complete amino acid profile and don't contain the "anti-nutrients" found in plants that can block mineral absorption.
Insulin-to-Glucagon Ratio.
Bikman also says that when a metabolically healthy person eats protein with low carbs, protein stimulates both insulin and glucagon, but because glucagon is also present, the body remains in a "fat-burning" state, and mTOR activation is balanced.
With a high-carb diet, insulin is already high and adding protein on top of a high-carb meal creates an "anabolic bomb" that spikes insulin further and shuts down fat-burning and autophagy entirely.
Protein Restriction is misguided
Bikman is against protein restriction for the average person, especially as they age. He identifies a condition called Anabolic Resistance, where older bodies need more protein (specifically leucine-rich animal protein) to trigger the same muscle-building signals that a young person gets from a smaller snack.
How does Bikman suggest we do this?
If you want the benefits of low mTOR (autophagy) and also the benefits of stronger muscles, don't starve yourself of protein. Instead, lower your carbohydrates. This keeps your baseline insulin low, allowing mTOR to cycle naturally. He also says eat protein with fat so as to stabilizes the insulin response.
How Much Protein overloads the system?
As of 2026, the research has moved away from a simple "yes or no", the answer depends entirely on your age, activity level and the source of the protein.
The Paradoxical Age Finding
A landmark study (Longo et al.) found that high amounts of protein is risky for those under 65 (increased cancer/mortality), but beneficial for those over 65 (higher protein actually reduced cancer/mortality in this age group by supporting the immune system).
Longevity science (LS) and protein consumption
LS looks at a different metric, not just "can you handle protein load," but "does it make you age faster?" If you are highly active (heavy weightlifting or intense cardio), your muscles act as a "sink" for protein. When you exercise, you create muscle damage and the protein you eat goes directly toward repair and recovery.
Because of this, the "pro-aging" signaling (mTOR) is balanced by the fact that you are clearing out damaged proteins through the exercise itself.
Sedentary" Danger
If someone is young and sedentary, and also eats very high amounts of protein the "growth signal" has nowhere to go. It just sits there telling your cells to grow, grow, grow stopping the "cleanup" (autophagy) process. The other problems they will face is excess calories from carbohydrates will be stored as body fat and they can become constipated. Eating high amounts of protein will typically contain about 2.5 to 3 grams of leucine, at these levels leucine is the specific amino acid which is the “On" switch for growth and the "Off" switch for cellular cleanup.
Note: New Research from 2024-2025 tells us that the body can absorb and use much larger amounts of protein than we think, (100g+) so we can build muscle, but this doesn't mean it’s healthy because of the shutting down of the anti-aging benefits of autophagy.
This doesn't necessarily mean everyone needs to eat a small amount of protein in a meal or protein overall, it is mainly about the person and the timing. By eating protein in a shorter window (Intermittent Fasting), you get the "muscle building" benefits during the day and the "autophagy/anti-aging" benefits at night. This strategy is called ‘Protein Pulsing’ but only works to your advantage if you are in that window of being very active, pregnant, bodybuilding OR you are over 65yo.
Important - once you hit your protein threshold, eating more protein doesn't necessarily make the muscle-building signal "stronger," but it does make it last longer. A 60g steak takes longer to digest than a 30g protein shake, keeping mTORC1 active for an extended period.
So, what is the difference between eating 30g and 60g of protein?
We need to look at how high does the signal goes and how long does it stay on.
- The Intensity (The "Satiation" Point)
The "muscle-building switch" (mTORC1) either hits the Leucine Threshold or it doesn’t. At 30g you have likely provided enough Leucine (~2.5g–3g) to fully saturate the mTORC1 response. This triggers maximum Muscle Protein Synthesis. (MPS) At 60g you don't necessarily get "double" the muscle-building signal. Once the cells are protein saturated, the intensity of the signal plateaus, you have told the body to "build," and it can only build so fast.
- The Duration (The "Autophagy" Problem)
This is where the major difference lies, with aging and autophagy. When you eat 30g of Protein there is a "clean" pulse and it is digested and processed relatively quickly. (roughly 2–3 hours depending on the source). When the amino acids are cleared from the blood, mTORC1 activity drops, allowing you to get back towards a "repair" state sooner. With 60g of Protein, this creates a much longer building phase because It takes the gut significantly longer to break down and absorb 60g of protein. This means amino acid levels remain elevated in the blood for 5–7 hours.
Note: 60g is only necessary if you are a high-level athlete with massive caloric needs, or if you are only eating two meals a day and need to hit your total protein goal.
Key Takeaway:
More protein doesn't build muscle faster, it just keeps the "growth" signal on longer—which is the enemy of autophagy.
Here is some information that will help you find your target protein threshold
Protein Threshold:
Finding that "ceiling" where more protein stops being a muscle-builder and starts being an expensive calorie source is a mix of science and listening to your body.
Here is how you can identify that limit:
Elderly - over 65yo
For people over 65, the timing of protein is often more important than the total amount. Younger adults can trigger muscle growth with as little as 20g of protein per meal, but older adults typically need a larger "spike" to overcome anabolic resistance.
• Optimal Dose: Aim for 30–40g of protein per meal. (3 x meals)
With protein pulsing you get the best of both worlds. (See below)
Here is a guide chart for the “Daily Protein Requirement” for various activity levels (younger adults and seniors)
1. Young & Sedentary• Target: 0.8 – 1.0 g per kg of body weight• Goal: Basic maintenance for those with desk jobs or low activity.
2. Seniors (Over 65)• Target: 1.2 – 1.5 g per kg of body weight• Goal: To overcome anabolic resistance and prevent muscle loss.
3. Moderately Active• Target: 1.2 – 1.5 g per kg of body weight• Goal: Recovery for those exercising 3–4 times per week.
4. Very Active / Endurance• Target: 1.5 – 1.8 g per kg of body weight• Goal: Repair for daily intense training or physical labor.
5. Bodybuilding / Strength• Target: 1.6 – 2.2 g per kg of body weight • Goal: Maximum muscle growth and protection during fat loss.
How to Find Your Personal Number
To get a ballpark figure, you can use this simple calculation:
1. Find your weight in kg
2. Multiply by 1.2 (This is for a sedentary person).
Target Grams = body weight (kg) x 1.2
Younger sedentary Person - Example: If you weigh 70kg, your effective ceiling is likely around 84g of protein per day. Anything beyond that is likely just wasted "extra" energy.
PROTEIN PULSING
I’ve been looking into the nutrition strategy called ‘Protein Pulsing’, and it’s kind of a game-changer. Instead of just eating all day, you time your protein to hit like a 'spike' for your muscles, and then you give your body 16 hours of 'cleanup time.' I must admit I don’t do it all the time, but when I do I’ve noticed way better focus in the morning, and I don't feel like I’m constantly dieting.
The reason why Protein Pulsing works
Instead of grazing on protein all day, which keeps the "growth switch" (mTOR) turned on 24/7, you consolidate your protein into fewer meals to create a clear biological "on" and "off" switch. To turn off the growth switch we need a window of at least 4 hours of not eating any protein, and 16 hours to clean up and get rid of unwanted cells.
To maximize both muscle preservation (turning mTOR "on" when needed) and longevity (turning it "off" to allow autophagy), you need to create "peaks and valleys" in your blood amino acid levels.
Protein Pulsing - 3 Common Objections
1. I could never skip breakfast; I’d be starving
Hunger is actually just a habit, after three days your hunger hormones reset and your body starts burning its own fat for fuel in the morning. You get energy and laser focus because you aren't
crashing from a morning bagel.
2. Don't you need to eat every 3 hours
That’s an old myth, if you eat small snacks all day your body never gets into 'cellular cleanup' (autophagy). Also by pulsing your protein in big hits, you signal your muscles to grow more than if you just trickled it in all day. Intermittent fasting keeps insulin levels low and stable, providing the brain with a steady stream of energy rather than a series of peaks and valleys.
When you eat frequently, your body constantly diverts blood flow and metabolic resources to the gut. The body isn't "broken" by frequent eating, but it is distracted. Constant digestion prevents the body from switching into "maintenance and repair" mode. Giving your gut a 4- to 5-hour break between meals (and a longer break overnight) allows those metabolic resources to be redirected toward cellular cleanup and mental clarity.
From an evolutionary standpoint, your brain is designed to be sharpest when you are hungry (to help you find food). Fasting triggers the release of norepinephrine, which heightens alertness and focus. Intermittent fasting and "protein pulsing" can increase the production of Brain-Derived Neurotrophic Factor (BDNF) helping mental clarity.
When your body is working how it should, by not eating for those 3-4 hours it will force your body to shift from burning glucose to burning ketones. (derived from fat)
When you eat every three hours, your body stays in a "fed state”, every snack or meal triggers an insulin response to manage blood glucose, leaving less "fuel" for high-level cognitive functions.
3. That sounds too complicated
It’s actually simpler. You only have to worry about three 'pulses.' You eat at noon then a high-protein snack at 4:00, and a big dinner at 8:00. No more 'what should I eat for breakfast'.
Note: These starting and finishing times can be moved but the timing in between must stay the same to get the benefit.
Summary Comparison: Frequent Eating vs. Intermittent Fasting
Eating Every 3 Hours
* Primary Fuel: Glucose (Fluctuating)
* Insulin Levels: Consistently High
* Mental State: Peaks and Valleys (Brain Fog)
* Cellular Repair: Low (Suppressed by mTOR)
Intermittent Fasting
* Primary Fuel: Ketones (Stable)
* Insulin Levels: Low/Baseline (body fat for fuel)
* Mental State: Steady Clarity
* Cellular Repair: High (Triggered by Autophagy
The "Low-Risk" Challenge, how to start
If it all sounds daunting, instead of committing for life, try a 3-day trial:
Start a 72 hour trial. From 8:00 PM tonight until noon tomorrow, just stick to water/black coffee. Then, at noon, have a high-protein lunch and see after 3 days what difference it has made to how you feel - what have you got to lose?
Important NOTE: No calories between 8:00 PM and noon, this is when the "cellular repair" called autophagy happens.
Protein Pulsing Schedule
8:00 PM – 12:00 PM | Fasting Phase
Action: No calories (Only Water/Black Coffee/Tea).
Purpose: Deep Autophagy and Fat Oxidation.
12:00 PM | Pulse #1
Action: 30g–50g Protein.
Purpose: Break the fast; trigger Muscle Protein Synthesis (MPS).
4:00 PM | Pulse #2
Action: 30g–50g Protein.
Purpose: Mid-day protein hit; second MPS spike.
8:00 PM | Pulse #3
Action: 30g–50g Protein.*
Purpose: Final meal; provides amino acids for the start of the fast.
*This amount can vary (see below) especially if you are more concerned with health issues and cellular cleanup. (Autophagy)
Quick Reminders:
• The Gap: Keep 3-4 hours between meals to reset your muscle-building signals.
• The Trigger: Aim for at least 35g of protein per meal to ensure you hit the "Leucine threshold."
Note: remember you can bring back your dinner meal to eat say at 6pm. That would mean your first 2 meals of the day would be 10am and 2pm.
Golden Rules for this Method
1. Hit the "Leucine Threshold"
For the pulses to work (especially if you are sedentary or over 65), you can't just have a "little bit" of protein at noon. You need enough to trigger the switch.• Aim for at least 35g of protein in that first meal. If you only eat 10g, mTOR won't fully activate, and you'll get the "worst of both worlds" (no autophagy, but no muscle growth either).
2. Avoid the "Hidden" Grazing
Small snacks are the enemy of autophagy. Even a splash of milk in your coffee or a small piece of jerky at 10:00 AM will spike your amino acids and kill the autophagy you worked for all morning. Rule: If you have anything in the 8-hour window, it must be zero-protein (water/plain tea/black coffee).
3. Prioritize "Whole" Proteins at Night
For your final meal at 6 or 7 or 8 PM, choose slower-digesting proteins (like steak, chicken,) rather than a fast-digesting whey shake.• Why: A steak can take 4–6 hours to fully digest, this creates a sustained "slow-drip" of amino acids into the bloodstream, keeping the muscle-building machinery running much longer into the night before the system eventually transitions into autophagy in the early morning.
Why this is safer than "Long Fasting"
Some people try to fast for 3–5 days for autophagy, but research shows this causes significant muscle loss (sarcopenia) in people especially over 50. The "daily pulsing" method gives you about 4 hours of high-quality autophagy every single day while ensuring your muscles get fed exactly what they need to stay strong.
Note: For those that say, “but the body can only assimilate around 30gm of protein at a time”, there is ample evidence available that says you can eat 100g+ of protein in one meal without it being "too much" for your health. Your body will absorb it all, although only about 30–50g will go directly toward immediate muscle building; ( see note below) the rest will support other bodily functions, be stored as fat or be used as fuel.
Note: The amount of protein that will go to building muscle will depend on your age, activity and how much resistance training you do.
The "Trigger" Threshold (20–35g)
Research suggests that for the average male, 20 to 35 grams of high-quality protein in a meal is the "sweet spot."• Why 20-35g? The mTOR threshold: This is enough to fully saturate Muscle Protein Synthesis (MPS).
The Autophagy threshold: While it does suppress autophagy, it is a transient spike. Most humans return to a "basal" (low-level) autophagic state within 3–4 hours after a meal of this size. Eating 80g+ in one sitting doesn't necessarily make the mTOR spike "higher," but it can make it last significantly longer, keeping autophagy suppressed for a much larger portion of the day.
The "Timing" Factor (Pulsing vs. Grazing)
The balance isn't found in a single meal, but in the frequency of those meals.
The Problem with Grazing: If you eat 15g of protein every 2 hours, you keep mTOR "simmering" all day. This is the worst of both worlds: you never hit the high threshold for muscle growth, but you also never drop low enough for deep autophagy.
The "Pulse" Solution: Spacing your protein intake into 3 distinct pulses (e.g., every 3 hours) allows mTOR to spike, to do its work, and then disappear. This creates "windows" where autophagy can resume between meals.
Practical Takeaway:
Building Muscle: If you are training hard and trying to put on size, don't starve your muscles at night. The "anabolic window" of sleep is too valuable.
If you are more concerned with general health and aging or have hit a weight-loss plateau, lowering protein at night is a powerful tool. It allows your liver and cells to shift from "construction mode" to "repair and maintenance mode" much earlier in the evening.
Note: Do what is right for you.
I want to now comment more about the mTOR. (mechanistic Target of Rapamycin complexes 1 and 2) Because my research continually makes me delve deeper into the nutritional health sciences, I have come to realise how important mTOR and its effects on the human body are.
Research on mTORC1 is currently at the center of longevity science. It acts as a "nutrient sensor"—specifically for amino acids, and functions like a cellular light switch. When "on," it triggers growth and protein synthesis; when "off," it triggers autophagy (cellular cleanup).
Recent studies (2024–2025) have moved away from the idea that protein is "bad" and toward a more nuanced protein intake.
The Latest Research on mTORC1 (2024-2026)
New research tells us that chronic activation of mTORC1 24/7, is what causes the harm, rather than the temporary spikes caused by a single meal.
In 2025, researchers identified rare genetic variants in long-lived individuals that naturally "recalibrate" mTORC1. (the 2025 Kolbe et al. study) These people don't have zero mTOR activity; they have a more efficient switch that flips between growth and repair more easily.
What can we do?
While you can't change your DNA, you can use lifestyle "bio-hacks" to mimic this fluid switching. This means making self-directed, strategic changes to your biology, diet, lifestyle, and environment to optimize health, performance, and longevity. You cannot perfectly replicate a rare genetic mutation that makes your cells 20% more efficient, but you can achieve 80% of the benefit through metabolic flexibility. (MF) MF is your body’s ability to switch between fuel sources based on what you eat.
Two Fuel States
1. The Glucose Burner (Fed State): After you eat a lot of carbs with high protein, insulin rises. Your body burns the sugar in your blood and stores the rest in your liver and muscles as glycogen or if you are metabolic inflexible you become a fat storer.
2. The Fat Burner (Fasted State): When you haven't eaten for several hours, insulin drops. Your body "flips the switch" to pull energy from your stored body fat and to produce ketones.
Note: Modern lifestyle—constant snacking and high-carb diets—keeps insulin levels chronically elevated. When insulin is always high, the "switch" gets stuck in glucose fat storing mode.
Signs you are metabolically inflexible
* If you miss a meal and get shaky, irritable, or dizzy, your body can’t access your fat stores for energy.
* Energy Crashes: You feel lethargic 2 hours after lunch.
* Difficulty Losing Weight: Even if you eat less, your body struggles to "unlock" your fat cells, because insulin is blocking the exit.
FINAL CONCLUSIONS:
The relationship between protein intake and longevity is not a simple linear equation; it is a delicate balancing act between growth and maintenance.
While chronic protein overconsumption keeps the mTOR pathway locked in "growth mode"—effectively silencing the body’s cellular cleanup processes, (autophagy) protein restriction carries its own set of perils, particularly the risk of sarcopenia and frailty in our later years.
The most promising path to longevity lies in metabolic flexibility rather than dogmatic restriction. By employing "Protein Pulsing," we can satisfy the body’s anabolic requirements to maintain muscle and bone density while intentionally creating windows of nutrient scarcity. This approach mimics the rare genetic efficiency found in centenarians, allowing the mTOR "switch" to flip fluidly between the building phase and the repair phase.
Ultimately, longevity is not merely the absence of disease, but the preservation of function. By timing protein intake, choosing slow-digesting sources at night to bridge the fasting window, and training the body to switch fuels efficiently, we can harness the benefits of protein for vitality without sacrificing the cellular "housekeeping" necessary for a long life. The goal is a recalibrated metabolism: a body that knows when to build, when to clean, and how to thrive in both states. Graeme
