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Growth factor and calorie restriction

Following animal studies that demonstrated calorie restriction could lengthen maximum lifespan, some people adopted calorie restriction with optimal nutrition (CRON) diets to lengthen their lives. These so-called CRONies eat significantly fewer calories than those on typical Western diets, and they tend to have less inflammation and lower levels of aging-related hormones, but a new study from nutrition researchers at Washington University School of Medicine in St. Louis has found that unlike laboratory rats and mice, people on calorie restriction don’t have lower levels of a key aging-related substance called IGF-1. The researchers say more study is needed, but it’s possible that in humans, reducing protein intake may be more important than cutting calories in slowing the aging process.

WHEN LABORATORY ANIMALS EAT ABOUT 25 PERCENT LESS, THEY LIVE ABOUT 50 PERCENT LONGER. THAT’S LED SOME PEOPLE TO ADOPT CALORIE RESTRICTION DIETS, NOT AS A MEANS OF LOSING WEIGHT BUT AS A WAY TO EXTEND THEIR LIVES. BUT A NUTRITION RESEARCHER AT WASHINGTON UNIVERSITY SCHOOL OF MEDICINE IN ST. LOUIS SAYS THAT IDEA MAY NOT WORK AS WELL IN PEOPLE AS IT DOES IN RATS AND MICE UNLESS THEY ALSO LIMIT THEIR PROTEIN INTAKE. JIM DRYDEN REPORTS …

ANIMALS ON CALORIE RESTRICTION LIVE LONGER THAN THEIR LITTERMATES. THOSE ANIMALS APPEAR TO LIVE LONGER BECAUSE OF CHANGES IN PATHWAYS INVOLVING INSULIN AND A GROWTH FACTOR CALLED IGF-1. SOME BELIEVE PEOPLE ON CALORIE RESTRICTION DIETS COULD LIVE TO BE 130 OR EVEN OLDER, BUT IT TURNS OUT THAT PEOPLE WHO CUT THEIR CALORIES BY 25 PERCENT OR MORE, DON’T SEEM TO HAVE THE SAME CHANGES IN THE IGF-1 PATHWAY, ACCORDING TO WASHINGTON UNIVERSITY NUTRITION RESEARCHER LUIGI FONTANA.

(act) :19 o/c no differences

In CR mice and rats on chronic CR, you have a reduction of about 30 to

40 percent in IGF-1, in circulating IGF-1. And it’s stable. So we said,

“What happens in humans?” So we are following this cohort of people who

are the CR Society members, and we measured IGF-1. No difference.

FONTANA SAYS ONE REASON MAY INVOLVE PROTEIN IN THE DIET. MANY MEMBERS OF THE CR SOCIETY, WHO PRACTICE CALORIE RESTRICTION WITH OPTIMAL NUTRITION AND CALL THEMSELVES CRONIES, EAT A LOT OF PROTEIN TO MAKE UP FOR SOME OF WHAT THEY LOSE IN CALORIES. FONTANA ALSO STUDIED IGF-1 LEVELS IN PEOPLE WHO DID CR FOR ONE YEAR AS PART OF A STUDY, AND THEIR IGF-1 LEVELS DIDN’T CHANGE MUCH EITHER.

(act) :19 o/c on CR

So we have the intervention data, and we have the long-term

data on these people that have been doing severe calorie

restriction. So that was puzzling because, you know, this was

the first time that we didn’t see an agreement between mice

and rats on CR and humans on CR.

THERE’S ANOTHER UNUSUAL GROUP THAT FONTANA ALSO FOLLOWS. THEY ARE STRICT VEGANS. AND ALTHOUGH THEY DON’T RESTRICT CALORIES AS MUCH AS CRONIES DO, THE VEGANS DO TEND TO EAT LESS PROTEIN. THEY HAVE LOWER LEVELS OF IGF-1.

(act) :21 o/c circulating IGF-1

And so we have this special population of vegan people. They have

low protein intake, and we compared them with the CRONies, with

the CR people. And we found that, in fact, these people, even if

they were heavier than the CR people, they have less, significantly

les, circulating IGF-1.

FONTANA SAYS MANY OF US EAT MORE PROTEIN THAN THE RECOMMENDED DAILY ALLOWANCE, OR RDA. AND HE SAYS THAT MAY BE THE REASON THAT IGF-1 LEVELS REMAIN HIGH FOR MANY PEOPLE, EVEN THOSE WHO PRACTICE CALORIE RESTRICTION. TO MAKE SURE, HE ASKED SOME MEMBERS OF THE CR SOCIETY TO CHANGE THEIR DIETS AND TO EAT LESS PROTEIN. THE RESULT WAS LOWER LEVELS OF IGF-1.

(act) :14 o/c lower IGF-1

After three weeks, IGF-1 dropped. So even if they were on a

severe calorie-restricted diet, high protein intake was, basically,

preventing them from having lower IGF-1.

HE SAYS CONSUMING ADQUATE PROTEIN IS IMPORTANT, BUT TOO MUCH MAY NEGATE SOME OF THE POSITIVE EFFECTS OF CALORIE RESTRICTION. HE REPORTS HIS FINDINGS IN THE JOURNAL AGING CELL. I’M JIM DRYDEN…

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