The abstract of a recent review paper nicely sums up the very high level view of what is known of the practice of calorie restriction in humans. No biochemistry here - just results and conclusions presently backed by science:

CONTEXT: Excessive calorie intake and subsequent obesity increases the risk of developing chronic disease and decreases life expectancy. In rodent models, calorie restriction with adequate nutrient intake decreases the risk of developing chronic disease and extends maximum life span. OBJECTIVE: To evaluate the physiological and clinical implications of calorie restriction with adequate nutrient intake. EVIDENCE ACQUISITION: Search of PubMed (1966-December 2006) using terms encompassing various aspects of calorie restriction, dietary restriction, aging, longevity, life span, adiposity, and obesity; hand search of journals that focus on obesity, geriatrics, or aging; and search of reference lists of pertinent research and review articles and books. Reviewed reports (both basic science and clinical) included epidemiologic studies, case-control studies, and randomized controlled trials, with quality of data assessed by taking into account publication in a peer-reviewed journal, number of animals or individuals studied, objectivity of measurements, and techniques used to minimize bias. EVIDENCE SYNTHESIS: It is not known whether calorie restriction extends maximum life span or life expectancy in lean humans. However, calorie restriction in adult men and women causes many of the same metabolic adaptations that occur in calorie-restricted rodents and monkeys, including decreased metabolic, hormonal, and inflammatory risk factors for diabetes, cardiovascular disease, and possibly cancer. Excessive calorie restriction causes malnutrition and has adverse clinical effects. CONCLUSIONS: Calorie restriction in adult men and women causes beneficial metabolic, hormonal, and functional changes, but the precise amount of calorie intake or body fat mass associated with optimal health and maximum longevity in humans is not known. In addition, it is possible that even moderate calorie restriction may be harmful in specific patient populations, such as lean persons who have minimal amounts of body fat.

All of this should be just as much common sense on diet and health as avoiding the accumulation of excess fat and exercising regularly.

Eat less, but obtain adequate nutrition - calorie restriction is not starvation

No-one knows the absolute, optimal, best level of calorie restriction for you - and no-one is likely to find out any time soon

But an 80/20, unoptimized practice of calorie restriction that costs little in time and effort and provides additional years of health appears to be a very practical goal

Experiment! Find a point that makes you feel healthier and your physician approve of your vital statistics

Involve your doctor in any sort of diet change for health reasons; everyone is different, and your doctor is there to help you understand whether you suffer from any medical condition that might put you at risk

The effects on general health in human trials are quite eye-opening, and the effects in long-running primate trials are even more so. If you can practice calorie restriction safely, then you owe it to your future self to look into it.

Take a little time to read through the following resources, set out there on the internet to help you: calorie restriction isn't anywhere near as hard as some folk make it out to be, and the benefits can be great.

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