That Clipperton Island was probably alright since there were inhabitants there for many years a century or more ago. The odd thing is that the island was mined for Guano (sea and bird shit), probably for fertilizer. And yet they ran out of food?
Unless of course they didn't trust the product themselves.
I suspect the modern epidemics of diabetes and other health issues are caused by fertilizer in our plant-sourced foods and drinks, and the lack of raw starches in our diet. I think the cooked or oxidized starches are to blame, and this is because I suspect the raw starches along with electrolytes and vitamins are what actually support and maintain the pancreas. Raw starches by nature are not oxidized. They are reducing agents that break down oxides instead. And that would be handy in protecting other reduction nutrients.
As an example, raw starches are converted to sugars by saliva. This behavior is normal and expected. But processed flours, bleached flours, cooked or baked starch products, crackers, rice, pasta, etc., never turn sweet in the mouth. Or only slightly.