Of Mice & Men – Dietary Edition

Nature Wants Us To Be Fat”, by Richard J. Johnson M.D., 268 pages, ISBN 978-163-7740347 (2022).

In these days of declining religion, instead of arguing about Catholic vs Protestant or Sunni vs Shia, many people seem to get strident about diet. The spectrum runs from vegans to carnivores, with aficionados apparently believing that those who do not share their beliefs are not only stupid but evil.

Dr. Johnson steps into this minefield with a new interpretation – the problem is fructose, a monosaccharide found in fruit, table sugar, and omni-present High Fructose Corn Syrup.

To over-simplify his argument, a few DNA mutations during the long period of human evolution gave some of our ancestors a great advantage – a “survival switch” – which allowed them to survive during periods of climatic adversity when food, especially winter food, was in short supply. The key to that survival switch was an oddity about the metabolism of fructose from fruits maturing during the Fall season. Fructose led to excessive eating and the formation of adipose fat in the body, which kept our ancestors alive over the winter.

It seems fairly reasonable that bears, subject to the same environmental pressures as our ancestors, developed a metabolism that caused them to gorge on fruit & berries in the Fall to carry them through hibernation over the winter. Since the starving body also produces water from fat when metabolized, it also seems reasonable that the camel developed a fat-filled hump – essentially a valuable store of nutrition & water in the difficult conditions of the desert. But one of the creatures which gains the most seasonal fat is the Emperor Penguin – and fruit is in as short supply in Antarctica as it is in the desert. One has to suspect that there is more to this story than fructose alone – and Dr. Johnson would agree.

Be that as it may, there is definitely a correlation between the obvious obesity epidemic sweeping the Western world and the explosion over the last half century in the use of High Fructose Corn Syrup and the now year-round availability of plentiful fructose-bearing fruits. Is correlation causation? Dr. Johnson’s hypothesis is that the modern diet essentially keeps the survival switch stuck in the “On” position year-round, instead of it providing only a beneficial seasonal temporary gain of fat. Hence obesity.

One of the fascinations of this book is Dr. Johnson’s exposition of his two decades of scientific research. The guys would hang around the lab chewing the fat and wondering – What if … Then they would breed another batch of genetically modified mice with particular genes activated or deactivated, and study how those mice compared to regular mice on various diets. Multiple lines of enquiry have provided strong support for the role of fructose in a “survival switch” … in mice. But as Dr. Johnson notes, they cannot perform similar tests on humans.

So what should we be eating or avoiding if the “survival switch” hypothesis turns out to be real? No surprise – it is the Mediterranean diet, albeit with limited amounts of fruit. And exercise. Always exercise.


“Eat food. Not too much. Mostly plants.”

– Michael Pollan

My take is the first and second parts are compelling, not clear the third one matters a lot. Staying away from e.g. seed oils probably makes sense. Balancing caloric intake with consumption has a shot at getting thermodynamics on your side :wink:

And then, for the truly dedicated to the cause of arguing how many angels could balance on the head of a pin, there are quantitative approaches falling under the nutrigenomics category.

Here is an interesting paper on that topic, however beware Betteridge’s law :wink: