I recently covered the topic of nutrition and aging - at least, energy restriction and protein restriction. Therein, I mention that calorie restriction has substantial amounts of research behind it in favor of it slowing the aging process. However, much of that evidence is in animals, because animals have much shorter lifespans than we do, and getting people to sign up for a 40 year randomized controlled trial where they are told to consume under what their body would normally need is 100% out of the realm of possibility. But, that doesn’t mean we can’t gain some human data from other types of studies.
For example, looking at associative studies, we might be able to tease out associations between underconsumption and lifespan extension. Interestingly, there is one group of people that actively believe in calorie restriction and have been calorie restricting themselves for years - this group of people belong to the Calorie Restriction Society and are currently being studied with hopes of getting some form of more controlled associative study to inform on the benefits. Still, as that research hasn’t released - what else can we lean on?
There have been randomized controlled trials, like the CALERIE study, that have put people on a mild calorie deficit for a couple of years and found numerous health benefits that would translate to a longer life, relative to if people didn’t enact this nutrition change. So, between the animal data, the CALERIE data, and some associative data, the evidence seems to lean toward ‘yes, calorie restriction leads to improvements in lifespan’. However, if these effects are mediated by lower energy consumption from food or from the indirect effect of reduced protein consumption is currently being debated - why?
Because there are studies that have reduced calories and specifically reduced protein, and when looking at a hormone called Insulin-like Growth Factor-1 (IGF-1), protein had massive IGF-1 reducing effects, while calorie restriction (while maintaining higher protein) had less effect. Since IGF-1 is thought to be one of the mechanisms for aging, there is some thought that protein restriction may be more effective than calorie restriction. Beyond that, animal protein restriction, which has more potent IGF-1 producing capabilities, may be even more beneficial.
While I can’t argue against this mechanism - I tend to be a bit more cautious in my interpretations, because relying on data based on one popular mechanism is insufficient evidence to convince me this is the right path to go. Still, I do think protein restriction is likely a benefit to lifespan; unfortunately, if done too drastically, can come at the serious cost of healthspan. There is likely a sweet spot where some level of normal healthspan can be maintained and majority of lifespan benefits can also be had - if you were to ask researchers like Dr. Valter Longo and these researchers looking at IGF-1 , that number is likely somewhere around 10% of calories coming from protein, which is very low and doesn’t leave much flexibility for exercise recovery.
There’s a lot more research that needs to be done, and hopefully we’ll get some new answers in the coming years (with the CHRON study in the Calorie Restriction Society), but at present, there is weak evidence that calorie restriction and possibly protein restriction do extend lifespan, although it may come at a cost of healthspan if not finely tuned - see previous article on ‘Reconsidering Aging’.
Nic  Most J, Tosti V, Redman LM, Fontana L. Calorie restriction in humans: An update. Ageing Res Rev. 2017;39:36-45. doi:10.1016/j.arr.2016.08.005 For Premium content, including detailed articles and videos: https://bit.ly/PhysionicInsiders2 Premium content + Consulting Lite: https://bit.ly/PhysionicInsidersPro