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Michael Greger MD

Michael Greger MD

Posted June 16, 2015

Published in Health

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Living Longer by Reducing Leucine Intake

Read More: Adventist Health Studies, aging, animal products, animal protein, apples, beans, cabbage, California, caloric restriction, chicken, China Study, cholesterol, dairy, Dr. T. Colin Campbell, eggs, enzymes, fish, fruit, grains, IGF-1, Japan, LDL cholesterol, leucine, lifespan, longevity, meat, mood, mortality, plant protein, plant-based diets, poultry, protein, rapamycin, side effects, standard American diet, TOR, turkey, vegans, vegetables, vegetarians

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NF-June16 How What We Eat (And Don't Eat) Impacts How We Age.jpg

Many studies have shown that calorie restriction, without malnutrition, can increase lifespan and lower the risk of age-related diseases, such as cancer.

However, for many people, calorie restriction clearly has its drawbacks. 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 (see Why Do We Age? for more on 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 a long list of potentially serious side effects. 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 (See my video Caloric Restriction vs. Animal Protein Restriction). If we look at the first comprehensive, comparative meta-analysis of dietary restriction, "the proportion of protein intake was more important for life extension 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. Protein restriction is much less difficult to maintain than dietary restriction, and it may even be more powerful because it suppresses both TOR and IGF-1, the two pathways thought responsible for the dramatic longevity and health benefits of caloric restriction.

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. Where is leucine found? Predominantly animal foods: eggs, dairy, and meat (including chicken and fish). Plant foods, such as fruits, vegetables, grains, and beans, have much less.

"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 nine pounds of cabbage--about four big heads--or 100 apples. These calculations exemplify the extreme differences in leucine amounts provided by a conventional 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 quasi-vegan diets of modest protein content tend to be relatively low in leucine."

This may also help explain the longevity of populations like the Okinawa Japanese, who have about half our mortality rate. The traditional Okinawan diet is only about 10% protein, and practically no cholesterol, because they ate almost exclusively plants. Less than one percent of their diet was fish, meat, eggs, and dairy - the equivalent of one serving of meat a month and one egg every two months. Their longevity is surpassed only by vegetarian Adventists in California, who have perhaps the highest life expectancy of any formally studied population in history.

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.

-Michael Greger, M.D.

PS: If you haven't yet, you can subscribe to my free videos here and watch my live year-in-review presentations Uprooting the Leading Causes of Death, More Than an Apple a Day, and From Table to Able.

Image Credit: hslo / Flickr

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