Regulators of health and lifespan extension in genetically diverse mice on dietary restriction

Abstract

SummaryCaloric restriction (CR) delays aging and extends healthy lifespan in multiple species. Alternative forms of dietary restriction (DR) such as intermittent fasting (IF) have drawn significant interest as a more sustainable regimen, but the landscape of longevity-promoting dietary interventions remains largely unexplored. Identifying the most robust, efficacious, and experimentally tractable modes of DR is key to better understanding and implementing effective longevity interventions for human healthspan. To that end, we have performed an extensive assessment of DR interventions, investigating the effects of graded levels of CR (20% and 40%) and IF (1 day and 2 days of fasting per week) on the health and survival of 960 genetically diverse female mice. All interventions extended lifespan, although only CR significantly reduced the mortality doubling time. Notably, IF did not extend lifespan in mice with high pre-intervention bodyweight. We carried out extensive phenotyping to determine the health effects of long-term DR and to better understand the mechanisms driving within-diet heterogeneity in lifespan. The top within-diet predictor of lifespan was the ability of mice to maintain bodyweight through periods of handling, an indicator of stress resilience. Additional predictors of long lifespan include specific changes in immune cells, red blood cell distribution width (RDW), and retention of adiposity in late life. We found that lifespan is heritable (h2= 0.24), and that genetic background has a larger influence on lifespan than dietary interventions. We identified a significant association for lifespan and RDW on chromosome 18 that explained 4.3% of the diet-adjusted variation in lifespan. Diet-induced changes on metabolic traits, although beneficial, were relatively poor predictors of lifespan, arguing against the long-standing notion that DR works by counteracting the negative effects of obesity. These findings indicate that improving health and extending lifespan are not synonymous and that metabolic parameters may be inappropriate endpoints for evaluating aging interventions in preclinical models and clinical trials.

Quantification of healthspan in aging mice: Introducing FAMY and GRAIL

“…Surprisingly based on previous literature suggesting CR works poorly when initiated late in life (25), both studies found that mice placed on either 20% or 40% CR lived significantly longer, while intermittent fasting did not significantly extend lifespan (23, 24). Calculating healthspan from the longitudinal frailty data, we found that 20% and 40% CR, but not intermittent fasting, significantly extended healthspan ( Fig.…”

“…This was somewhat difficult, as several studies we examined collected healthspan data either at single time points or from only a subset of animals whose lifespans were also determined. Fortuitously, two recent studies collected longitudinal frailty data and determined the lifespan of genetically heterogeneous Diversity Outbred (DO) mice on one of several different diet regimens (23, 24). In these studies, mice were placed on ad libitum (AL) diet, intermittently fasted (1D and 2D represent groups that fasted once or two consecutive days per week in the first study, respectively, while IF1 and IF2 represent mice that were fasted either one or two days per week in the second study, respectively), or placed on either a 20% or 40% CR diet (CR20 and CR40, respectively).…”

“…(A-B) Survival and healthspan (FAMY) of DO mice fed the indicated diets from 2.5 years of age were plotted and calculated using the surivial and frailty data from Luciano et al , 2024 (23). (C) Healthspan (FAMY) of DO mice fed the indicated diets from 6 months of age was calculated during the surivial and frailty data from Di Francesco et al , 2023 (24). …”

“…In these studies, mice were placed on ad libitum (AL) diet, intermittently fasted (1D and 2D represent groups that fasted once or two consecutive days per week in the first study, respectively, while IF1 and IF2 represent mice that were fasted either one or two days per week in the second study, respectively), or placed on either a 20% or 40% CR diet (CR20 and CR40, respectively). The primary difference between the studies is that diets were initiated at 6 months of age in the first study (24), and initiated at 2.5 years of age in the second study (23).…”

Late-life dietary folate restriction reduces biosynthetic processes without compromising healthspan in mice

“…Lastly, we note that male and female mice on the folate-limited diet maintained their weight better as they aged than their counterparts on the folate-replete diet (Figure 2), likely through increased adiposity. A recent study identified these phenotypes as top predictors for positive effects on health and lifespan in genetically diverse mice on various dietary restriction diets (Di Francesco, A. et al, 2023).…”