By Dmytro Gospodaryov and Oleh Lushchak
The idea of extending life expectancy by modifying diet originated in the mid-20th century when the effects of caloric restriction were found. It was first demonstrated on rats and then confirmed on other model organisms. Fasting activists like Paul Bragg or Roy Walford attempted to show in practice that caloric restriction also helps to prolong life in humans.
For a long time the crucial question in this research concerned finding a molecular mechanism that demonstrated how caloric restriction might promote longevity. The discovery of such a mechanism is possible with very simple organisms whose genetics were well understood and whose genes could be switched on or off. For example, the budding yeast, nematodes and fruit flies are windows into the complicated genetics of longevity. Several discoveries have been made in recent years, including resveratrol, sirtuins, insulin growth factor, methuselah gene, Indy mutation.
The effects of caloric restriction may be more complex than anticipated. Protein-to-carbohydrate ratio has been shown to play a large role in diet response. Additionally, medical concerns about danger of refined sugar and fructose for health have gained recognition, typically relating to high-mortality diseases and disorders, such as diabetes, diabetic complications, and obesity.
Following an initial study of antioxidant system of the budding yeast, we turned our sights to biogerontological studies after the discovery of possible molecular mechanism of resveratrol action in yeast model. However, we quickly realized that the fruit fly (specifically Drosophila) is likely a better model because we could then also investigate behavioural outcome and food intake. How would caloric restriction and the amount of carbohydrates in the diet affect the longevity of fruit flies?
We posed the question of whether the type of carbohydrate fed would affect mortality in fruit flies, including fructose, glucose, a plain mixture of the two, and sucrose (a disaccharide composed from monomers, fructose and glucose). We wanted to see whether fructose is a “poison” or “toxicant” as can be found in publications or popular lectures of Professor Robert Lustig.
We found, surprisingly, that flies fed on sucrose ceased to lay eggs after several weeks of adult life, and sucrose shortened their mean life span at all concentrations above 0.5% total carbohydrate. On the other hand, we found that fruit flies were quite well adapted for living on fructose. Furthermore, this effect was not observed for plain mixture of fructose and glucose.
The results were surprising because sucrose is routinely used in laboratory recipes of fly food. Lower fecundity on sucrose was also unexpected. However, we realized that the effects we had observed in the study would not lead us to immediate sugar denialism. The fly food used in the study was quite different from usual fly food, and in human context resembled likely a spicy marmalade diet.
Nonetheless, it is known that egg laying in Drosophila is promoted by dietary proteins (taken up mostly from yeasts). The diets of our flies contained a very small amount of protein, and yet this deficiency did not interfere with egg laying on monosaccharides while disaccharide sucrose caused dramatic loss in fecundity.
Is it possible to apply our current data to human physiology? It seems to be rather difficult to build assumptions on healthy diet of humans based on the data obtained for insects. The insect physiology with their specific development hormones, probably different metabolism and metabolic demands stands far away from that of humans. Nevertheless, the general message is that the influence of diet on ageing cannot be reduced to simply amount of calories, or macronutrient balance. The quality of nutrients, the micronutrients, the peculiarities of digestion, including gut microbiota, should also be taken into account. While scientists are often forced to simplify models, to gain a better understanding of molecular, biochemical, genetic, and physiological grounds of ageing, our understanding would likely benefit from bringing a variety of researchers, from ecologists and mathematicians, into the discussion.
Dr. Dmytro Gospodaryov is Assistant Professor and Dr Oleh Lushchak is a researcher at the Department of Biochemistry and Biotechnology at Vasyl Stefanyk Precarpathian National University. They are the co-authors of “Specific dietary carbohydrates differentially influence the life span and fecundity of Drosophila melanogaster” in The Journal of Gerontology: Biological Sciences. Their research interests comprise the influence of dietary components on survival, oxidative modification of proteins, and roles of different redox-active compounds within cells.
The Journals of Gerontology® were the first journals on aging published in the United States. The tradition of excellence in these peer-reviewed scientific journals, established in 1946, continues today. The Journals of Gerontology, Series A® publishes within its covers The Journal of Gerontology: Biological Sciences and The Journal of Gerontology: Medical Sciences.
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