In an interesting series of experiments, researchers found evidence for a diet of old tissues to modestly reduce life span in flies and mice. If speculating on specific mechanisms, we might look to the various forms of metabolic waste and damaged proteins that accumulate with age; some of that might find its way past the digestive process to be incorporated into tissues and thereby accelerate the aging process. This sort of dietary influence on aging is already a much-debated topic regarding advanced glycation end-products, for example. The results of the studies here offer reinforcement for the SENS approach of damage repair to create rejuvenation, but sadly that is not the conclusion reached by the researchers involved. They instead look ahead to a much harder task with the prospect of only marginal benefits, which is to say safely altering cellular metabolism in order to slow down damage accumulation. This is an inferior approach to periodic damage repair, requiring far more research to realize, and capable of producing only lesser gains in health and life span.
A study offers evidence bolstering one long-held theory: that aging is caused, at least in part, by molecular damage accumulating in the cells. This damage is generated by nearly every cellular process by the work of enzymes and proteins and the life-sustaining metabolic processes that occur at every level of complexity, from simple molecules and cell components to whole cells and entire organs. Over time we have many, many damage forms, byproducts of enzyme function, for example, or of protein-to-protein interactions, errors in DNA transcription or translation. As a function of age, they accumulate, and eventually, it's more than the body can cope with.
Researchers found that feeding a diet of "old" organisms to yeast, fruit flies, and mice shortened their lifespans by roughly 10 percent. Here's how it worked: for yeast, the researchers formulated one cell-culture medium composed of extracts from young yeast cells and another of extracts from old ones. They then grew new yeast cells on each medium and watched to see which set would live longer. "Our hypothesis was that as yeast ages, it accumulates certain damage forms, and we wanted to test that specific damage and find out if it is deleterious for yeast." The team replicated the same basic procedure in fruit flies and mice: they collected 5,000 freshly dead flies that had lived an average of 45 days, and sacrificed 5,000 others that were three to five days old. Then they prepared two homogenized diets, one composed of young flies and the other using the old ones. They fed these diets to young female fruit flies. The mice were fed diets of skeletal muscle from young and old farmed red deer (three years old versus 25) that replaced the animal-product components (insects, carrion, worms, etc.) of a normal mouse diet. Using mouse tissue was not feasible because of the large quantities needed for the experiment; deer meat was a suitably close match.
The experiments raise new questions - in a field that's full of them - and some of the results were a little unexpected. The researchers had expected to see larger differences in the test organisms' relative lifespans. The effect was consistent, however, across all three species. In the study, the authors interpret the minor-but-consistent effect to mean that damage accumulation may be only one contributing factor in aging, and also that damage caused by internal molecular changes may have a stronger effect than damage introduced through the diet. It's also likely that the damage arises from many processes. "And they all work together in a deleterious way. So the question is, how do we slow down this process? How do we restructure cellular metabolism so that this damage accumulates at a slower rate?"