Human Calorie Restriction Studies Continue Apace

Studies of the biochemistry of calorie restriction (CR) in humans are being held in a number of research institutes in the US. So far, as expected, the beneficial biochemical changes caused by CR in humans look very much like the biochemical changes observed in mice, rats, and rhesus monkeys. That bodes well for a gain in human life span as a result of this practice, though at the present level of available biotechnology there is little option but to wait and see what the results will be on that count. The consensus amongst biogerontologists appears to be that CR will extend human life span by a handful of percentage points, but practitioners of calorie restriction would be expected to evade or resist all of the common age-related diseases.

Biologist Michael Rose, known for his work on aging in flies, is a calorie restriction (CR) skeptic, it would seem. He and John Phelan have developed a mathematical model that predicts a "lifetime of low-calorie dieting would only extend human life span by about 7 percent, unlike smaller animals, whose life spans are affected more by the effects of starvation. ... Longevity is not a trait that exists in isolation; it evolves as part of a complex life history, with a wide range of underpinning physiological mechanisms involving, among other things, chronic disease processes."

Bear in mind that estimates for the expected difference in human life span between people who exercise regularly and people who do not exercise regularly are in the range of 10 years, give or take a few years. There is no medical technology available today that can achieve anywhere near these sorts of results.

In any case, you might look at this recent paper which examines CR in healthy, thin people:

Calorie restriction (CR) slows aging and is thought to improve insulin sensitivity in laboratory animals. In contrast, decreased insulin signaling and/or mild insulin resistance paradoxically extends maximal lifespan in various genetic animal models of longevity. Nothing is known regarding the long-term effects of CR on glucose tolerance and insulin action in lean healthy humans.

In this study we evaluated body composition, glucose, and insulin responses to an oral glucose tolerance test and serum adipokines levels in 28 volunteers, who had been eating a CR diet for an average of 6.9 +/- 5.5 years, (mean age 53.0 +/- 11 years), in 28 age-, sex-, and body fat-matched endurance runners (EX), and 28 age- and sex-matched sedentary controls eating Western diets (WD).

We found that the CR and EX volunteers were significantly leaner than the WD volunteers. Insulin sensitivity [was] significantly higher in the CR and EX groups than in the WD group (P = 0.001). Nonetheless, despite high serum adiponectin and low inflammation, approximately 40% of CR individuals exhibited an exaggerated hyperglycemic response to a glucose load. This impaired glucose tolerance is associated with lower circulating levels of IGF-1, total testosterone, and triiodothyronine, which are typical adaptations to life-extending CR in rodents.

As for other human studies of CR, it shows that the CR metabolism is better set up for long term health and avoidance of age-related disease.

ResearchBlogging.orgFontana L, Klein S, & Holloszy JO (2009). Effects of long-term calorie restriction and endurance exercise on glucose tolerance, insulin action, and adipokine production. Age (Dordrecht, Netherlands) PMID: 19904628