Science Fair Project Encyclopedia
Caloric restriction (CR) is the practice of limiting dietary energy intake to improve health and retard aging. In human subjects, CR is known to slow the signs of aging, as indicated by biomarkers such as cholesterol and blood pressure. Every animal species tested with CR so far, including monkeys, rats, spiders and rotifers, has shown corresponding lifespan extension. CR is the only known dietary measure capable of extending maximum, as opposed to average, lifespan. Energy intake must be minimised, but sufficient quantities of vitamins, minerals and other important nutrients must still be taken. To emphasise this, CR is often referred to as CRON or CRAN (caloric restriction with optimal or adequate nutrition.)
While scientists knew about the effects of CR since the 1930s, the first major demonstration of the benefits of caloric restriction was an experimental trial conducted by Richard Weindruch. In 1986, Weindruch reported that restricting the calorie intake of laboratory mice proportionally increased their lifespan compared to a group of mice with a normal diet. The calorie-restricted mice also maintained youthful appearances and activity levels longer, and showed delays in age-related diseases.
The findings have since been accepted, and generalised to a range of other animals. Researchers are investigating the possibility of parallel physiological links in humans (see Roth et al below). In the meantime, many people have independently adopted the practice of caloric restriction in some form, hoping to achieve the expected benefits themselves.
Why CR increases longevity
Recent research has demonstrated (see Matthias Bluher , C. Ronald Kahn , Barbara B. Kahn , et al.) that it is not reduced intake which influences longevity. This was done by studying animals which have their metabolism changed to reduce insulin uptake, consequently retaining the leanness of animals in the earlier studies. It was observed that these animals can have a normal dietary intake, but have a similarly increased lifespan.
This suggests that lifespan is increased for an organism if it can remain lean and if it can avoid any accumulation of fatty tissue: if this can be done while not diminishing dietary intake (as in some minority eating patterns, see e.g. Living foods diet or Joel Fuhrman) then the 'starvation diet' anticipated as an impossible requirement by earlier researchers is no longer a precondition of increased longevity.
Other recent research by Prof. Leonard Guarente shows that the gene SIR2 in yeasts or SIRT1 in mice is released, when fat is released from storage cells. Extra copies of this gene extended the lifespan of the animal even without CR. His work was published in the June 2004 issue of the science magazine Nature. His research is not finished yet. See also ENSEMBL gene database for information on SIRT1.
- The retardation of aging in mice by dietary restriction: longevity, cancer, immunity and lifetime energy intake. Journal of Nutrition, 116(4), pages 641-54.Weindruch R, et al.,April, 1986.
- Caloric Restriction and Aging Richard Weindruch in Scientific American, Vol. 274, No. 1, pages 46–52; Januarytits
- 2-Deoxy-D-Glucose Feeding in Rats Mimics Physiological Effects of Caloric Restriction. Mark A. Lane, George S. Roth and Donald K. Ingram in Journal of Anti-Aging Medicine, Vol. 1, No. 4, pages 327–337; Winter 1998.
- Biomarkers of caloric restriction may predict longevity in humans. Roth GS, Lane MA, Ingram DK, Mattison JA, Elahi D, Tobin JD, Muller D, Metter EJ.: 297: 811, Science 2002.
- Eat more, weigh less, live longer, New Scientist, January 2003.
- Extended longevity in mice lacking the insulin receptor in adipose tissue. Bluher, Khan BP, Kahn CR, Science 299(5606): 572-4, Jan 24, 2003.
- Interview,I want to live forever, Cynthia Kenyon Professor of Biochemistry and Biophysics at the University of California, San Francisco, by James Kingsland. New Scientist online, 20th October 2003.
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