Laboratory experiments from a variety of animals, most notably rodents, suggests that energy restriction may increase longevity. In particular, animals exposed to low energy intake for much of their life are protected from diseases associated with ageing, and may also increase maximum lifespan through unknown mechanisms. Extrapolation to humans is tempting, although no solid observable evidence is available to conclusively show that energy restriction increases lifespan in humans. However, certain populations around the World to consume low energy foods for much of their lives and these populations do show greater longevity compared to Western populations. Whether this is due to a reduction in the risk of degenerative diseases associated with ageing or due to an actual increase in maximum life span, however, is not fully understood. Low energy foods also tend to be of higher quality which further muddies the understanding of the cause of the association between energy intakes and longevity.
Many populations around the World are noted for their longevity. These populations tend to be rural living and consume their traditional diet. The Okinawan people live on the Ryukyu Islands which include Okinawa in the pacific Ocean close to Japan and this population still retains many of its traditional practices including its traditional diet. This diet includes substitution of the usual Japanese rice with the sweet potato, and this is supplemented with vegetables, including soy, and small amounts of fish and pork. One of the characteristics of the diet of the Okinawans as a whole is the lower energy intake when compared to other Japanese cultures. In fact the Okinawan people have been estimated to consume around 83 % of the energy of a typical mainland Japanese individual. This is coupled with death rates from cardiovascular disease, cancer and stroke that are only 60 to 70 % that of populations on the mainland of Japan. Okinawan all cause mortality rates are roughly half those for mainland Japan.
A large part of the protection from Western diseases and protection from all cause mortality may come from the lifestyle of the Okinawan populations. They tend to live less stressful lives that are of a slower pace. Such slower pace of life is also characteristic of other traditional populations around the World and is typified by the Mediterranean population of Sicily, a traditional population renowned for its longevity and health. However, diet likely contributes to the health of the Okinawans, and evidence suggests diet protects significantly from the development of Western lifestyle diseases such as cardiovascular disease and cancer. The energy restrictive nature of the Okinawan people is not surprising, as their diet is based on plant foods that are by their nature relatively energy sparse due to the high water and fibre content. The limited inclusion of animal proteins and the almost absence of processed foods therefore decreases the energy content of the diet as a whole relative to typical Western intakes.
Studies have been conducted on the elderly populations of Okinawa, who would have been septuagenarians at the time. From these studies it was found that the energy intake during the life of these individuals was around 11 % lower than would be recommended for maintenance of body weight, suggesting that in the long term they under consumed energy. One important point that is obvious from this data is that it further disproves the energy balance theory of weight gain and weight loss. Clearly after consuming 11 % too few calories the Okinawan people did not continue to lose weight, suggesting that energy regulation is more complex that considered by many. Of course the Okinawans are a genetically isolated population and so genetic factors should always be considered to play a part in their longevity. However, that low energy intakes are associated with longevity may simply be an artifact of the fact that low energy diets tend to contain high amounts of plant based foods, and these by their nature are protective of disease.
RdB
