The hunger games as the key to happily ever after?

Abstract

The world's human population is reaching record longevities. Consequently, our societies are experiencing the impacts of prolonged longevity, such as increased retirement age. A major hypothesised influence on ageing patterns is resource limitation, formalised under calorie restriction (CR) theory. This theory predicts extended organismal longevity due to reduced calorie intake without malnutrition. However, several challenges face current CR research and, although several attempts have been made to overcome these challenges, there is still a lack of holistic understanding of how CR shapes organismal vitality. Here, we conduct a literature review of 224 CR peer-reviewed publications to summarise the state-of-the-art in the field. Using this summary, we highlight challenges of CR research in our understanding of its impacts on longevity. We demonstrate that experimental research is biased towards short-lived species (98.2% of studies examine species with <5 years of mean life expectancy) and lacks realism in key areas, such as stochastic environments or interactions with other environmental drivers (e.g., temperature). We argue that only by considering a range of short- and long-lived species and taking more realistic approaches, can CR impacts on longevity be examined and validated in natural settings. We conclude by proposing experimental designs and study species that will allow the discipline to gain much-needed understanding of how restricting caloric intake affects long-lived species in realistic settings. Through incorporating more experimental realism, we anticipate crucial insights that will ultimately shape the myriad of socio-bio-economic impacts of senescence in humans and other species across the Tree of Life.