Study says restrict protein, not calories

[Guest guest]

Study shows IGF-1 (insulin-like growth factor-1), is not reduced by CR

in humans as it is in animals. Humans on 6-year CR show IGF-1 levels

similiar to the regular sedentary population. Comparing the CR group

to a vegetarian group shows lower IGF-1 in vegetarians.

Dave

Link:

http://www.sciencedaily.com/releases/2008/09/080924151018.htm

Text:

Differences Between People And Animals On Calorie Restriction

ScienceDaily (Sep. 26, 2008) — Calorie restriction, a diet that is low

in calories and high in nutrition, may not be as effective at

extending life in people as it is in rodents, according to scientists

at Washington University School of Medicine in St. Louis.

Previous research had shown that laboratory animals given 30 percent

to 50 percent less food can live up to 50 percent longer. Because of

those findings, some people have adopted calorie restriction in the

hope that they can lengthen their lives. But the new research suggests

the diet may not have the desired effect unless people on calorie

restriction also pay attention to their protein intake.

In an article published online this month in the journal Aging Cell,

investigators point to a discrepancy between humans and animals on

calorie restriction. In the majority of the animal models of

longevity, extended lifespan involves pathways related to a growth

factor called IGF-1 (insulin-like growth factor-1), which is produced

primarily in the liver. Production is stimulated by growth hormone and

can be reduced by fasting or by insensitivity to growth hormone. In

calorie-restricted animals, levels of circulating IGF-1 decline

between 30 percent and 40 percent.

" We looked at IGF-1 in humans doing calorie restriction, " says first

author Luigi Fontana, M.D., Ph.D., assistant professor of medicine at

Washington University and an investigator at the Istituto Superiore di

Sanità in Rome, Italy. " For years, we have been following a cohort of

people from the CR Society who have been on long-term calorie

restriction. We found no difference in IGF-1 levels between people on

calorie restriction and those who are not. "

The CR Society members, who call themselves CRONies (Calorie

Restriction with Optimal Nutrition), had been on a calorie-restriction

diet for an average of seven years when Fontana did the measurements,

but their IGF-1 levels were virtually identical to sedentary people

who ate a standard, Western diet.

Because calorie restriction is linked to extraordinary increases in

maximal lifespan in rats and mice, Fontana and colleagues at

Washington University, including principal investigator O.

Holloszy, M.D., professor of medicine, have been involved in a

scientific study that compares calorie restriction to exercise and

measures many biological factors linked to longevity and health.

Called the CALERIE study (Comprehensive Assessment of the Long term

Effects of Reducing Intake of Energy), the project randomly divided 48

people into three groups: Eighteen cut their caloric intake by 25

percent for one year. Another 18 started exercising to increase their

energy expenditure by 25 percent for a year. A third group of 10

people didn't change anything.

At the end of that year, the investigators measured IGF-1 levels in

all three groups. Again they found no reductions in the group on

calorie restriction.

" That was puzzling because it was the first time we hadn't seen

agreement between mice and rats on calorie restriction and humans on

calorie restriction, " Fontana explains. " But we know there are two

major influences on IGF-1 levels: calorie intake and protein intake.

So we decided to look at the influence of protein. "

Again, Fontana had a ready-made study group. His team has been

following a population of strict vegans for several years. They tend

to eat less protein than the CRONies from the CR Society, so he

compared IGF-1 levels between the two groups.

" The vegans had significantly less circulating IGF-1, even if they

were heavier and had more body fat than CRONies, " he says. " Protein in

the diet seemed to correlate with the lower levels of IGF-1. The

strict vegans took in about 10 percent of their total calories from

protein, whereas those on calorie restriction tended to get about 23

or 24 percent of calories from protein. "

The investigators wanted to take one more look at the relationship

between dietary protein and IGF-1, so Fontana asked a group of CRONies

to eat less protein for a few weeks. He says it was not easy to cut

protein because those on calorie restriction have to do a lot of

calculating and juggling to ensure they take in very few calories and

still get adequate nutrition. Increasing dietary protein is one way

many CRONies guard against becoming malnourished.

" But six of them agreed to lower their protein intake, " Fontana

explains, " and after three weeks their circulating IGF-1 declined

dramatically. "

Previous research from Fontana's group had found that a diet lower in

protein might protect against some cancers. These more recent findings

suggest lowering protein also might be important to longevity. Fontana

admits his evidence is preliminary, but the findings suggest that when

people adjust their diets to improve health and lengthen life, they

should control not only calories and fat but also keep an eye on protein.

Fontana isn't proposing radical low-protein diets. Instead, he is

suggesting the current recommended daily allowance (RDA) for protein,

which is 0.82 grams of protein per kilogram of body weight, or about

56 grams of protein for an average, adult man and 46 grams for an

average, adult woman. Most people, including CRONies, consume much

more protein than the RDA recommendation.

" It's much easier to restrict protein than to restrict calories, " he

says. " If our research is on the right track, maybe humans don't need

to be so calorie restricted. Limiting protein intake to .7 or .8 grams

per kilogram per day might be more effective. That's just a

hypothesis. We have to confirm it in future studies. "

Until then, Fontana suggests people might want to look at protein

consumption and tailor it to RDA recommendations. Traditionally, he

says, nutritionists have not worried about people eating too much

protein, but these findings suggest perhaps they should.

Journal references:

1. Fontana et al. Long-term effects of calorie or protein

restriction on serum IGF-1 and IGFBP-3 concentration in humans. Aging

Cell, 2008; 7 (5): 681 DOI: 10.1111/j.1474-9726.2008.00417.x

2. Fontana L, Klein S, Holloszy JO. Long-term low-protein,

low-calorie diet and endurance exercise modulate metabolic factors

associated with cancer risk. American Journal of Clinical Nutrition,

vol. 84; pp. 1456-1462, Dec. 2006