Archived Research: 
Caloric restriction and disease prevention strategies

Research into the possible use of caloric restriction to prevent or delay age-related diseases is focusing on several areas:

• Immune function
• Cancer
• Other disease prevention in humans
   
  

Immune function
The ability to resist infection declines with age, in animals and in humans. In mammals, at least some of this impairment of immunity is believed to be due to a decline in the function of specialized white blood cells called T cells. In a Japanese study of calorie-restricted mice, T-cell function was dramatically better than in the freely fed mice. In a study published in Clinical Immunology in December 2002, researchers found that mice afflicted with colitis and fed calorie-restricted diets showed improved T cell function over freely fed mice. This led to improved immune response to the colitis and a reduction in the severity of the condition. Whether the boost T cells receive from caloric restriction will translate to better overall infection-fighting ability remains to be determined.

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Cancer
The incidence of many cancers increases with age. Certain long-lived strains of mice are noted for their high risk of developing lymphoma (cancer of the lymph nodes) and hepatoma (liver cancer). In a University of Wisconsin study, that strain when subjected to caloric restriction had a cancer incidence of 38% compared to the freely fed control mice, whose tumor incidence was 78%. Another study in mice documented that caloric restriction reduced the rate of all cancers by about half.

This protection from cancer may be due to an improved effect on the body's capacity to repair damaged DNA. Researchers at Wayne State University found that caloric restriction reverses an age-related decline in a certain type of DNA repair called base excision repair, giving older animals the same ability to repair damaged DNA as younger ones. The study, published in March 2003, also showed that this enhanced base excision repair capacity corresponded to a reduced mutation frequency when the animals were exposed to carcinogens.

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Other disease prevention in humans
Most studies of caloric restriction in humans have been preliminary, observational and involving few subjects. One famous (and inadvertent) study took place in Biosphere II, intended to be a self-contained, self-sustaining greenhouse and colony in the desert of Arizona. Unanticipated problems with food production led to a reduction in the participants' daily calorie intake to about 1,500 calories per day, largely in the form of grains, vegetables, beans and fruits. Gerontologist Roy Walford of UCLA, a participant himself and one who followed a calorie-restricted diet voluntarily for years, studied his fellow calorie-restricted subjects. He found improvements in their total blood cholesterol levels, blood pressure and glucose levels. The study was too short and the participants mostly young adults, so extrapolations to aging adults are premature, but the results are provocative nevertheless.

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