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).
Images thanks to Great Beyond via Flickr.
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 practice it. There’s got to be a better way to suppress the aging engine 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, its 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 restricting calories, but from restricting 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 DR 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 protein 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 9 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 vegetarian or vegan diet. The functional role of leucine in regulating TOR activity may help explain the extraordinary results reported in the Cornell-Oxford-China Study, since quasi-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. Less than one percent of their diet was fish, meat, eggs, and dairy - 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.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Ariel Levitsky.
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What’s TOR? Make sure you go back and 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 in that case. Both leucine and methionine content may be additional reasons why Plant Protein is Preferable.Other reasons why those eating plant-based diets may live longer:
This all may help explain the results of Harvard’s Meat and Mortality Studies.
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