Discuss the relationship between calorie restriction diet and longevity
Calorie restriction (CR) diet consists of reducing the daily calorie intake by up to 40% without removing nutritional value, (Willcox et al., 2007, Katsman et al., 2010). The emphasis is based on under-nutrition and not mal-nutrition. The Okinawa diet seems to have a CR status for two main reasons, the first being that Okinawa had reduced food supplies in the first half of the 19th century and secondly the locals needed a high calorie intake to support their daily needs as vocational farmers. Together the low calorie intake coupled with high physical activity levels produced a local situation of CR estimated to be approximately 11% lower than their normal requirements. The local food types, dense in nutrients and low in calories are another factor leading to the mythical longevity of Okinawa centenaries, (Heilbronn & Ravussin, 2003, Willcox et al., 2007).
CR is the most potent means of extending lifespan and reducing age related disease in test animals (Vigeneau-Callahan, 2001, Heilbronn & Ravussin, 2003, Willcox et al., 2007). CR has been extensively explored on animals since the 1930s because of its ability to extend mean and maximum life span and delay or even prevent most age related disease. CR affects metabolism, hormonal balance, and the generation, detoxification and resistance to oxidisation, (Vigeneau-Callahan, 2001). Only one long-term test (>30 years) has linked CR to human longevity, reporting lower all-cause mortality in humans with a CR of 15%. CR of 50% increased risk of death. This data was consistent with previous findings in animals. It is impossible to maintain long-term energy deficit and health, which is why it is important for the nutritional value of a CR diet to be retained with specially selected foods yet still allowing the calorie intake to be reduced, (Heilbronn & Ravussin, 2003, Willcox et al., 2007). Calorie restriction in juveniles has a detrimental effect in growth and development. If the diet is poor in nutritional value as well as in calorific value then juvenile development can produce impaired fertility, impaired growth, and immune capabilities, and adverse psychological effects, (Heilbronn & Ravussin, 2003). The longer the period of CR the greater effect on longevity, however brief periods of CR of less than a year can also increase longevity, (Shanley & Kirkwood, 2000).
Longevity is an elongated lifespan that can be one of the effects resulting from calorie restriction (CR). In rodents it has been observed up to extend the lifespan up to 20-40%, (Shanley & Kirkwood, 2000). CR has successfully extended lifespan in essentially all tested animals, (Vigneau-Callahan, 2001). The calorie restriction diet also has other effects that are part of the general physiological process that happens in the body during CR. These include an increase in gluconeogenesis and a decrease in glycolysis, the liver takes a dominant role because of the loss of fat mass, (Kubova & Guarente 2003). The liver makes keytones that result from the degradation of fat and proteins in test animals, (Kubova & Guarente 2003). The liver also needs to produce less Insulin like Growth Factor taking some of the stress off it. Gluconeogenesis is the synthesis of new glucose not from glycogen. This alternative production of glucose is necessary for use in the brain, testes, erythrocytes and kidney medulla because glucose is the only energy source these organs use, (King, 2011).
A change also occurs in hormonal balance including a reduction of lactation, reduced levels of Insulin like Growth Factors, Reduced Growth Hormone and Gonadotropins, (Kubova & Guarante, 2003). Also including infertility, not applying to male rodents with CR in late-life. Females regain function when CR returns to normal and can be fertile to a later age, however if it is present during early life in male rodents it may be irreversible, (Shanley &...