Caloric Restriction vs. Animal-Protein Restriction

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The lifespan extension associated with dietary restriction may be due less to a reduction in calories, and more to a reduction in animal protein (particularly the amino acid leucine, which may accelerate aging via the enzyme TOR).

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Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

Although the beneficial effects of caloric restriction on lifespan and health have been clearly demonstrated, it is difficult to implement such restrictions in our lives.” In the classic Minnesota Starvation Study, many of the volunteers suffered a “preoccupation with food, constant hunger, binge eating,” and lots of emotional and psychological issues. “Even researchers who study caloric restriction rarely practise it.” There’s got to be a better way to suppress the engine-of-aging enzyme, TOR.

That’s why researchers were so excited about rapamycin, a drug that inhibits TOR, thinking it could be caloric restriction in a pill. But, like any drug, it’s got side effects, too. There’s got to be a better way.

The breakthrough came when scientists discovered that the benefits of dietary restriction may be coming not from the restriction of calories, but from the restriction of protein intake. If we look at “the first comprehensive comparative meta-analysis of [dietary restriction],…the proportion of protein intake was more important for life extension via [dietary restriction] than the degree of caloric restriction.” In fact, just reducing protein, “without any changes in calorie level, have been shown to have similar effects as caloric restriction.”

That’s good news, because “[p]rotein restriction is much less difficult to maintain than dietary restriction, and may be more powerful than dietary restriction,” because it suppresses both TOR and IGF-1—the two pathways thought responsible for the “drastic longevity and health benefits” of caloric restriction.

And, some proteins are worse than others. One amino acid in particular, leucine, appears to exert “the greatest effect” on TOR. In fact, just cutting down on leucine may be “nearly as effective” as cutting down on all protein. So, where is leucine found? Predominantly animal foods: eggs, dairy, and meat, including chicken and fish, whereas plant foods have much less: fruits, vegetables, grains, and beans.

“In general, lower leucine levels are only reached by restriction of animal proteins.” To reach the leucine intake provided by dairy or meat, we’d have to eat like nine pounds of cabbage—that’s like four big heads of cabbage—or 100 apples. “These calculations exemplify the extreme differences in leucine amounts provided by [a more standard diet] in comparison to a [plant-based] diet.” “The functional role of leucine in regulating [TOR] activity” may help explain the extraordinary results reported in the Cornell-Oxford-China Study, since “[q]uasi-vegan diets of modest protein content tend to be relatively low in leucine.”

This may also help explain the longevity of long-lived populations like the Okinawa Japanese, who have about half our mortality rate. The traditional Okinawan diet was only about 10% protein, and practically no cholesterol, because they ate almost all plants. Only one percent of their diet was fish; meat, eggs, and dairy, less than one percent—the equivalent of one serving of meat a month; one egg every two months. Their longevity surpassed only by vegetarian Adventists in California, “giving them perhaps the highest life expectancy of any formally described population in history.” And now, we may be a little closer to answering the mystery as to why populations eating plant-based diets live the longest.

Please consider volunteering to help out on the site.

Images thanks to Great Beyond via flickr

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

Although the beneficial effects of caloric restriction on lifespan and health have been clearly demonstrated, it is difficult to implement such restrictions in our lives.” In the classic Minnesota Starvation Study, many of the volunteers suffered a “preoccupation with food, constant hunger, binge eating,” and lots of emotional and psychological issues. “Even researchers who study caloric restriction rarely practise it.” There’s got to be a better way to suppress the engine-of-aging enzyme, TOR.

That’s why researchers were so excited about rapamycin, a drug that inhibits TOR, thinking it could be caloric restriction in a pill. But, like any drug, it’s got side effects, too. There’s got to be a better way.

The breakthrough came when scientists discovered that the benefits of dietary restriction may be coming not from the restriction of calories, but from the restriction of protein intake. If we look at “the first comprehensive comparative meta-analysis of [dietary restriction],…the proportion of protein intake was more important for life extension via [dietary restriction] than the degree of caloric restriction.” In fact, just reducing protein, “without any changes in calorie level, have been shown to have similar effects as caloric restriction.”

That’s good news, because “[p]rotein restriction is much less difficult to maintain than dietary restriction, and may be more powerful than dietary restriction,” because it suppresses both TOR and IGF-1—the two pathways thought responsible for the “drastic longevity and health benefits” of caloric restriction.

And, some proteins are worse than others. One amino acid in particular, leucine, appears to exert “the greatest effect” on TOR. In fact, just cutting down on leucine may be “nearly as effective” as cutting down on all protein. So, where is leucine found? Predominantly animal foods: eggs, dairy, and meat, including chicken and fish, whereas plant foods have much less: fruits, vegetables, grains, and beans.

“In general, lower leucine levels are only reached by restriction of animal proteins.” To reach the leucine intake provided by dairy or meat, we’d have to eat like nine pounds of cabbage—that’s like four big heads of cabbage—or 100 apples. “These calculations exemplify the extreme differences in leucine amounts provided by [a more standard diet] in comparison to a [plant-based] diet.” “The functional role of leucine in regulating [TOR] activity” may help explain the extraordinary results reported in the Cornell-Oxford-China Study, since “[q]uasi-vegan diets of modest protein content tend to be relatively low in leucine.”

This may also help explain the longevity of long-lived populations like the Okinawa Japanese, who have about half our mortality rate. The traditional Okinawan diet was only about 10% protein, and practically no cholesterol, because they ate almost all plants. Only one percent of their diet was fish; meat, eggs, and dairy, less than one percent—the equivalent of one serving of meat a month; one egg every two months. Their longevity surpassed only by vegetarian Adventists in California, “giving them perhaps the highest life expectancy of any formally described population in history.” And now, we may be a little closer to answering the mystery as to why populations eating plant-based diets live the longest.

Please consider volunteering to help out on the site.

Images thanks to Great Beyond via flickr

Doctor's Note

What’s TOR? Be sure to watch my “prequel” video, Why Do We Age?

This reminds of the study I profiled in The Benefits of Caloric Restriction Without the Actual Restricting.

Methionine is another amino acid that may be associated with aging; see Methionine Restriction as a Life-Extension Strategy to find out which foods to avoid. Both leucine and methionine content may be additional reasons why plant protein is preferable (see Plant Protein Preferable).

Other reasons why those eating plant-based diets may live longer:

 This all may help explain the results of Harvard’s Meat & Mortality Studies.

Update: I have a couple of newer videos on caloric restriction. See:

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