On Mar 16, 12:09 am, "Caleb" wrote:
This was the first article in Science News this week. Very interesting
article, and it may well be that regular dieting and weight loss is
not such a bad thing -- it might even be better in some ways than
maintaining a stable weight.

Very interesting descriptions and the follow-ups will be intriguing.

Yours,

Caleb

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from:http://www.sciencenews.org/articles/20070310/fob1.asp

Week of March 10, 2007; Vol. 171, No. 10 , p. 147
Living Long on Less? Mouse and human cells respond to slim diets

Patrick L. Barry

Scientists have known since the 1930s that mice and other animals live
30 to 50 percent longer when placed on a diet that's low in calories
yet nutritionally complete. The unanswered question has been whether
calorie restriction has the same life-extending effect on people.

Direct proof of a payoff for human longevity would take decades. But
scientists have now shown that people on a calorie-restricted diet
experience many of the cellular changes reported in mouse studies.

"The experimental results [in mice] mirror the results we found," says
Anthony E. Civitarese of the Pennington Biomedical Research Center in
Baton Rouge, La. Whether those changes would extend a person's life
remains uncertain, he notes.

As people get older, energy-converting organelles called mitochondria
decrease in number and generate greater amounts of harmful by-products
called free radicals. Many scientists hypothesize that DNA damage from
these by-products can cause chronic diseases of old age such as
cancer.

Civitarese and his colleagues randomly assigned 36 overweight people
to one of three groups. The first group was instructed to follow a
diet with 25 percent fewer calories than the individuals' initial
energy expenditures. Each participant in the second group followed a
diet with 12.5 percent fewer calories than he or she had initially
expended, while exercising to burn another 12.5 percent. Both diets
contained adequate nutrition. People in the third group ate a weight-
maintenance diet, the researchers report in the March PLoS Medicine.

During the 6-month study, participants in both calorie-restricted
groups showed a 20 to 35 percent increase in the number of
mitochondria in their muscle cells and a 60 percent decrease in DNA
damage. The mitochondria appeared to become more youthful and
efficient.

People in the calorie-restricted groups also showed increased activity
of several genes related to mitochondrial function. Scientists have
long considered one of these genes, SIRT1, to be crucial for animals'
responses to calorie restriction.

"Not only is it a good study, but it's the only kind that we can do"
practically, comments David Sinclair of Harvard Medical School in
Boston. Several companies, including one cofounded by Sinclair, are
developing drugs to activate SIRT1.

"It's exciting to see SIRT1 in the middle of this," says Leonard
Guarente of the Massachusetts Institute of Technology, a cofounder of
a competing company. However, he says that interpretation of the
results of the Baton Rouge study is limited because the participants
were overweight, a condition that can accelerate tissue aging.

The researchers enrolled overweight people in part because they would
be motivated to follow a strict diet, Civitarese says. His team is
planning a test that will focus on people of normal body weight and
last 2 years.

Too much of a good thing, might not be good overall however. The mice
in question living longer is one thing, but the kind of restriction
they use for mice can result in decreased development, including
smaller BRAIN size. That is not one trade off most people would chose
for living longer. Probably, a restrictive diet is ok for adults
though as long as you are within the healthy medical weight range for
your height. Some of us even feel it might be best to be near the
bottom of that range, but like you say we won't know the answer to
that until after many years of study. dkw