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Today we will discuss three relatively unknown subjects: the ‘engine of aging’ enzyme (TOR), an adrenal steroid hormone (DHEA), and an amino acid called methionine.

All may have serious repercussions on the length of our lives as well as our risk of cancer.

And each may be controlled by the consumption of the right type of protein.

Let me explain.

Taming TOR

Let’s start with an explanation of TOR.

Nicknamed the ‘engine of aging’ enzyme, TOR functions as a master regulator of cellular growth and proliferation.

TOR gets its name (Target of Rapamycin) because it can be inhibited (‘targeted’) by the drug rapamycin, an antifungal produced by a bacterium first isolated on Easter Island. In mammals, it is called mTOR (for mechanistic or mammalian TOR), and rapamycin has been used as an immunosuppressant in humans to prevent rejections of transplanted organs.

While we need it early on in life to grow, high levels of mTOR in adulthood seem to be linked to a significantly higher risk of cancer as well as premature death.

Perhaps the best way to describe mTOR is to employ the analogy of a speeding car. When you are young and growing, it is okay for the car (mTOR) to go ‘fast.’ You need cells to proliferate and grow in infancy and early life.

However, when you enter the low-speed zone of adulthood, cell growth needs to slow down. But if mTOR is continuously stimulated (by what we eat among other things), that will not happen.

mTOR is the engine of growth in childhood but the engine of aging in adulthood.

Studies show that in almost 100 percent of advanced human prostate cancers, mTOR is present in higher amounts. Similarly, higher levels of mTOR are found in breast cancer tissues and appear to be associated with advanced disease and worse overall survival rates.

Simply put, if you suppress mTOR, you may reduce your risk of cancer and increase your chances of living longer.

So what is the best way to do that?

One strategy to stem mTOR production (and in turn extend lifespan) seems to be the severe restriction of calorie consumption.

When food is abundant, mTOR soars, encouraging body cell division. However, when there is scant food, mTOR shifts into conservation mode and slows down cell division, kicking in a process called autophagy (literally translated as to ‘eat oneself’), which cleans and renews cells.

A better way to reduce mTOR production is to restrict animal protein intake.

One of the drivers of mTOR appears to be the amino acid leucine, which is found in higher amounts in animal foods (e.g. dairy, meat, chicken, fish, and eggs).

Therefore, to lower your leucine intake (and mTOR levels), you need to either restrict your consumption of animal proteins or, better yet, adopt a 100 percent plant-based diet. (While plant foods contain small amounts of leucine, it is nothing in comparison to animal proteins.)

Eating plants—and specifically cruciferous veggies—decreases mTOR activation and provides natural mTOR inhibition. Some of the best mTOR-inhibiting fruits and veggies include broccoli, green tea, soy, turmeric, grapes, onions, strawberries, blueberries, and mangoes.

You only have to look at the example of the older generation Okinawa Japanese for evidence that this approach seems to work. For centuries, the extremely long-lived Okinawans have traditionally consumed a largely plant-based diet; only a scant 1 percent of their diet was made up of fish, meat, eggs, and dairy.

Reducing our animal protein intake (versus restricting calories) is a much easier approach when it comes to decreasing mTOR levels—and also a more powerful one.

That is because lowering the consumption of animal protein will not only suppress mTOR production but also decrease IGF-1 levels as we discussed in our article The Protein Question (while calorie restriction will lower mTOR but not IGF-1).

What About DHEA?

Let us now turn to the topic of DHEA.

The most abundant steroid hormone in the human body, DHEA (dehydroepiandrosterone) may also be associated with the longevity benefits attributed to dietary restriction.

As we age, the level of DHEA in our bodies drops significantly.

So while we want to decrease mTOR production, we would like to increase DHEA.

One way to raise DHEA is—once again—to restrict calorie consumption.

But probably the best path to naturally boosting your DHEA levels is through nutrition—specifically by eating a plant-based diet.

Research shows that the amount of DHEA in the blood increases as much as 20 percent after only five days of adhering to an egg-free vegetarian diet (compared to meat eaters consuming equivalent amounts of calories).

And even more interestingly, these levels rise not necessarily because the body is producing more DHEA but because a plant-based diet causes the body to lose less in the first place.

More About Methionine

Last but not least, let’s turn to the third subject in our protein triumvirate: methionine.

An important scientific article published 40 years ago indicated that many human cancer cells are ‘absolute methionine dependent.’  More specifically, the study showed that normal cells grown in vitro without methionine seemed to thrive while cancer cells died.

Two decades later, this methionine dependence was further reported in 5 types of fresh patient tumors (e.g. colon, breast, ovary, prostate, and melanoma) grown in vitro.

In other words, unlike ‘healthy’ tissues, some human tumors seemed to require the amino acid methionine to grow.

So, when you lower methionine, you may reduce your cancer risk.

Restricting high methionine animal foods and consuming a plant-based diet that is naturally low in it may do just that.

For Senior Citizens Only

One question I am frequently asked when discussing protein is this:

What is the optimal source and amount of protein for senior citizens?

Sedentary individuals over the age of 65 lose about 1 percent of their muscle mass every year while older adults on bed rest can lose muscle mass 6 times faster than a younger person.

Physical activity is one of the best approaches to halt muscle mass loss later in life.

Another way to protect aging muscles is to eat vegetables; you can cut your odds of losing muscle mass by 50 percent just by consuming the daily recommended servings of veggies.

Why does eating vegetables help?

A recent study showed that a plant-based diet was positively associated with muscle mass in women aged 18-79 years old. It appears that the alkalizing effect of veggies may neutralize the mild metabolic acidosis that occurs with age—the same extra acid that stimulates the breakdown of muscle.

A chronic low-grade acidosis with advancing age is associated with declining kidney performance. But it is also a result of a Western dietary pattern (or the ‘meat-sweet’ diet), which is high in acid-promoting animal and sugary foods while low in alkalinizing fruits and veggies.

So we have covered three protein-related topics today: mTOR (and leucine), methionine, and DHEA. All three play an important role in our aging process and risk of cancer. In the case of mTOR (leucine) and methionine, levels should go down or stay low, while we need to keep our DHEA levels high.

And this can be easily accomplished by consuming primarily or exclusively plant-based proteins found in fruits, vegetables, legumes, whole grains, and nuts.

Rosane Oliveira, DVM, PhD

President & CEO, Plant-Based Life Foundation | Dr. Rosane Oliveira combines a lifelong passion for nutrition with 25 years of genetics research to create programs that help people develop healthy habits on their journey towards a more plant-based lifestyle. She is a Visiting Clinical Professor in Public Health Sciences and was the founding director of the first Integrative Medicine program at the UC Davis School of Medicine. She completed her postgraduate studies in Brazil and did her postdoctoral training in immunogenetics and functional genomics at the University of Illinois at Urbana-Champaign.