Hot off the Press In just the past couple of years, a brand-new and extremely important metabolic pathway was discovered. Researchers were studying a naturally occurring substance known as rapamycin, which is synthesized from soil bacteria, as it was able to demonstrate some fairly powerful cancer-inhibiting properties. Drug companies were extremely interested in finding out how it worked and accidentally stumbled across this new, previously unknown metabolic pathway, now referred to as mTOR, which stands for “mammalian target of rapamycin.” Much as insulin serves as a sort of default sugar sensor and leptin serves as the body’s fat sensor, mTOR (it turns out) serves as the body’s protein sensor, monitoring the availability of protein, or amino acids (particularly the branched-chain amino acids, most notably leucine, as well as methionine), for growth and reproduction.
It is also influenced by insulin levels, impacting IgF-1 activity, and is part of a related metabolic pathway. When protein levels are detected that exceed our basic maintenance requirements, the excess levels up-regulate the activity of the mTOR pathway, stimulating cellular proliferation and adverse (from a longevity standpoint) mitochondrial effects. Increased insulin also has this effect, and the mTOR protein belongs to what is known as the P13K pathway, which is activated by insulin, nutrients, and growth factors. mTOR has a central role in the regulation of cell growth and protein synthesis. It essentially activates our reproductive and cell-proliferating capacity.
It makes sense that dietary protein in excess of what is needed for maintenance and repair would send a message that it might be a good time to reproduce or make more cells. It is well known that animals in the wild whose diets are restricted by reduced food availability also typically have fewer young or may even fail to reproduce in a particular year, depending upon the available energy supply. Protein availability seems to be the key limiting factor. What is less stimulating of reproductive processes, however, is ultimately more stimulating of individual regeneration, repair, and enhanced mitochondrial function. This is where it gets interesting.
A recent study stated, “It has been shown that limiting dietary amino acids, specifically methionine, inhibits signaling through mammalian target of rapamycin (mTOR) thereby decreasing mitochondrial damage and protein translation” (Rosedale et al. 2009).
The effect, in plain language, is slowed aging and improved health. Again, cellular proliferation occurs mainly under three circumstances: reproduction (DNA replication and pregnancy); growth, as, for example, in children; and cancer. A presentation on April 14, 2008, at the American Association for Cancer Research annual meeting revealed that modified caloric restriction may offer a protective effect against the development of epithelial cancers.
Epithelial cancers, also known as carcinomas, arise in the tissue that lines the surfaces and cavities of the body’s organs, and they make up 80 percent of all cancers. “Calorie restriction and obesity directly affect activation of the cell surface receptors’ epidermal growth factor and insulin-like growth factor,” explained study coauthor Tricia Moore, a graduate student in the Department of Carcinogenesis at the University of Texas’s M. D. Anderson Cancer Center. “These receptors then affect signaling in downstream molecular pathways such as Akt and mTOR. Calorie restriction, which we refer to as negative energy balance, inhibits this signaling, and obesity, or positive energy balance, enhances signaling through these pathways, leading to cell growth, proliferation, and survival.”
If, however, the dietary protein level stays below this threshold, ancient mechanisms kick in that are designed to help us outlive an apparent famine, which then shuts down cellular proliferation and up-regulates, instead, repair and regeneration.
This process signals an effort to keep us healthy enough, long enough, so that our cells can reproduce another day. Our energy is conserved through maintaining our own cellular repair instead of making new cells. That’s what we want! We want just enough protein to meet the demands of our own repair, regeneration, and basic maintenance needs that can extend our own longevity, enhance our own health, and possibly even reverse signs of aging, but not so much that we up-regulate mTOR.
And we always want to keep insulin levels as low as possible.
So, how much is just enough? For most adults the RDA, roughly 0.8 g per kilogram (2.2 pounds) of ideal body weight (e.g., 150-pound ideal body weight (68 kg) × .8 g = 54 g), is probably sufficient for 97.5 percent of the adult population (one of the rare RDAs worth paying some attention to). The average would lie somewhere between 45 and 60 g of actual protein per day for the majority of adults. One study noted that the amount of protein needed to effectively retain lean tissue mass and quality physical performance in athletes was closer to 1.2 to 1.7 g/kg daily, translating to 60 to 80 g of protein per day, assuming adequate mineral intake (Phinney 2004). The same study also noted negative effects if this level of daily protein was exceeded by more than 25 percent of the daily energy expenditure, citing a drop in performance and suppression of ketogenesis. Note: Keep in mind that when we’re talking about grams of protein, we’re not saying grams of meat or fish. Protein is only a part of what makes up meat or fish. Fat, water, and many other nutrient components make up a piece of meat or fish.
Trevrizent!! You are almost there! 
