Based on the posting "How Much Should We Eat", at nutritionadvocate.com
Edited (with Introduction) by Dr. Don Rose, Writer, Life Alert

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The first person I ever read about who advocated restricting calorie intake in order to prolong life was Dr. Roy Walford, "credited with significantly furthering research on the discovery that laboratory mice, when fed a diet that restricted their caloric intake by 50% yet maintained nutritional requirements, could more than double their expected lifespan."[1] Walford was also part of the initial crew of Biosphere pioneers; Biosphere 2 -- designed as a self-contained testbed for future space colonization missions - was a perfect place to reduce one's calories, since rules allowing no one in or out for two years meant no ordering pizza. In fact, during his stay "in Biosphere 2, the crew found that they could not grow as much food as anticipated, so Dr. Walford convinced the crew to follow his calorie restriction diet. It is claimed that this action 'produced dramatic weight loss and improved health.' " [1,2]

Other researchers have built upon Walford's work. This article discusses one such example, a Hawaiian-Japanese study, which lends further evidence to the theory that reducing one's energy intake (for example, eating less, or eating lower-calorie foods, or both) can add more years to your life, and more life to your years.

Should seniors try diets that dramatically lower calorie intake? Certainly older Americans need to be careful about calories, since metabolism tends to slow with age; love handles and beer bellies are not exactly associated with youth. Although studies do indicate that "less is more" (less calories usually means more health), always consult your doctor before any dietary change -- and rapid extreme weight loss is never recommended. But since increased calories typically leads to weight gain and fat accumulation, restricting rather than raising seems to be the direction to go. --Dr. Don Rose

Increasing longevity via caloric restriction
Researchers in Hawaii and Japan are reporting remarkable results about the association between energy intake and mortality from a 36-year follow-up study to the Honolulu Heart Program. Their findings are consistent with previously reported results.

Laboratory animal studies - from the 1930's - observed that energy restriction prolongs life span and decreases risk for a wide range of age-related diseases. Low energy intake extends the lifespan in species as diverse as protozoans, fruit flies, spiders, guppies, chickens, and dogs. These animal studies indicate that energy intake above a certain level shortens the lifespan, whereas lower intake -- to a certain level (usually up to 50%-60% of the group mean) -- results in a lifespan extension of up to 50%!

Epidemiological studies of human populations in Japan observed a strong relationship between low energy consumption and long life. The Okinawan Japanese, in particular, consume the least calories of any Japanese group and have the longest life expectancy, the highest percentage of centenarians, and the lowest mortality from diabetes, heart disease, and several cancers.
Don't go too low
The Hawaiian researchers observed benefits only when caloric intake fell between 15% and 50% of the group mean. Benefits ceased and mortality increased when caloric intake fell below 50%. Conversely, mortality increased even in non-obese individuals who consumed calories at the level of 15% of the group mean or higher.
Conclusion
Findings from the study imply that what health professionals consider to be "normal" energy intakes may be too high. This study suggests that the less food we eat (without becoming too extreme), the better our health.
References
[1] http://en.wikipedia.org/wiki/Roy_Walford

[2] http://www.lef.org/magazine/mag2004/oct2004_itn_01.htm
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