If by “cellular repair and recycling” you mean autophagy, the most honest scientific answer is this: there is no proven universal protein number that every person should hit to trigger it. The biology shows that low amino acid availability, especially lower leucine signaling, can reduce mTOR activity and make autophagy more favorable, but human research has not established a single exact daily gram target that guarantees this effect in everyone.

That means the common idea that protein must be kept extremely low, such as under 20 grams per day, is too simple to be scientifically solid. Protein is not just a switch for growth. It is also the raw material your body uses to maintain muscle, enzymes, immune defenses, hormones, and tissue structure. For most healthy adults, standard reference intakes are about 0.8 to 0.83 grams per kilogram of body weight per day, which is already far above 20 grams for most adults.

So how low should protein be if the goal is more cellular cleanup rather than growth? Scientifically, the safest answer is that it should be lower than your usual intake only temporarily, not chronically pushed to a severely low level. The mechanism seems to depend more on creating a low nutrient, low amino acid, low growth-signaling state than on hitting one magic protein number. In practice, that means the concept is about temporary protein restriction or fasting physiology, not about trying to live long term on a near-deficiency intake.

The reason caution matters is that too little protein for too long can backfire. Autophagy is a recycling process, but if nutrient deprivation becomes excessive or prolonged, the body can move beyond healthy turnover and into tissue breakdown. Research on low protein states and severe energy deficit shows that excessive catabolism can contribute to muscle wasting, and studies on lifelong protein restriction suggest harmful effects on muscle fibers and neuromuscular health.

So the practical conclusion is not “keep protein as low as possible.” It is “do not confuse temporary signaling with a permanent requirement.” If your goal is to encourage repair and recycling, the science supports brief periods of lower nutrient signaling more than chronic protein deprivation. There is no strong evidence that most adults should stay below the normal protein requirement for long periods just to improve cellular renewal, and there is growing reason to think that doing so could cost muscle, strength, and resilience.

A more accurate way to say it is this: protein likely needs to be low enough to reduce amino acid and mTOR signaling for a limited time, but not so low for so long that the body begins sacrificing important tissue. Science can describe the mechanism, but it does not currently give a clean universal cutoff like “X grams per day for everyone.” For most people, the baseline requirement is still the safer long-term floor, and any intentional period of much lower intake is better thought of as a short intervention, not a lifestyle.

In plain terms, the best scientific answer is this: low protein may help create conditions for cellular recycling, but there is no exact proven number, and going too low for too long becomes more likely to cause breakdown than healthy renewal.