Let's be careful not to conflate life expectancy and life span. The former being dominated[1] by improvements in reducing infant mortality and mothers dying during child birth, while the latter has remained largely consistent[2],[3].

‘… life expectancy in the mid-Victorian period was not markedly different from what it is today. Once infant mortality is stripped out, life expectancy at 5 years was 75 for men and 73 for women.’[1]

[1]-https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2625386/

[2]-https://www.bbc.com/future/article/20181002-how-long-did-anc...

[3]-https://www.sapiens.org/biology/human-lifespan-history/

Edit - sources ordered incorrectly.

And back then also a lot of other factors were less than ideal. (Including lack of medication and medical science altogether.) The idea behind cold and hungry is not being that cold for that long and that hungry. Definitely not starving to death.

What Sinclair hypothesizes that the reason behind the phenomena they see is that these adverse conditions trigger mechanisms in our body that are beneficial in the long term. And the very reason might be to try to make up for what causes the the lower life expectancy. Not knowing much about the topic and the mechanism, my other thought was that it tries to slow your ageing so that you can be fertile for longer in a bid to be able to reproduce when the rough times are over.

So the idea is to kick in the protective mechanisms but still cause no real damage. Similarly to how you're better off eating less than what the average person does in any obese society. Even though their life expectancy is still higher than what it was 500 years ago.