Temperature affects your body's sugar uptake. I believe that it is not insulin sensitivity so much as non insulin basal glucose uptake. Type 1 diabetics have a tendency toward low blood sugar in very hot weather, and high blood sugar in cold weather. (which always seemed counter intuitive to me, as my assumption would be that shivering would qualify as exercise which would drop blood sugar, but there must be some accompanying liver dump)

This is a great question, I am convinced insulin sensitivity is related to the seasons, so many other things are, including sleep patterns and fat distribution in the body, for instance. Seasonal change and food availability would have been the overriding influence on every facet of Paleolithic Life, so I assume every function in the body is tuned into it.

I therefore think it is really important to eat what is found in season in your own country, like fruits only in late summer and autumn, spring veggies and sprouted seeds in spring, mushrooms and nuts in autumn etc. and this means, growing them ourselves, foraging for them in nature or going to the farmers' market and seeing what is on offer from stalls that don't sell bananas and avocados (unless you live in the tropics).

I think insulin production is far more complex than we realize and plays many, many more (seasonally sensitive) roles than we have yet to discover, so, it just makes sense to go with the seasons.....

Vitamin D is known to have some function of maintaining insulin sensitivity, so higher carb consumption in summer would most likely be offset by higher vitamin D blood levels.

Fantastic question.

Have you read Lights Out: Sleep, Sugar, and Survival? The book is a bit wild and I think off-base at times, but does make some strong points about seasonality and diet.

Back to your question: Is insulin sensitivity seasonal; and if so, should we eat seasonally?

My answer is that:

A) it appears reasonable to assume so....dependent on your heritage, and how close to the equator your ancestors might have been 10,000 years ago.

B) even if A) is true -- can we eat seasonally? I live in Southern California, and for all intents and purposes, it is summer all year-round - which I love BTW. But perhaps I am missing out on an important metabolic cycle? I dunno.

i'm starting to lose weight again after plateauing in the winter. don't know if it's related to more sun or not. i live in the northeast.

I think this is a very interesting topic and definitely look forward to more thorough investigation of this idea by people such as Robb Wolf, and the other fantastic bloggers out there...

However I think in the grand scheme of things, that many of plants beneficial compounds aren't necessarily part of an evolved adaptation, its such a side effect of chemical interactions, and studies of epidemiology, amongst other things...

From Wikipedia on Blueberries:

Blueberries contain anthocyanins, other antioxidant pigments and various phytochemicals possibly having a role in reducing risks of some diseases,[19] including inflammation and certain cancers. Blueberry anthocyanins, proanthocyanidins, resveratrol, flavonols, and tannins inhibit mechanisms of cancer cell development and inflammation in vitro."

Now there might well end up being a great argument for the fructose in blueberries to only be ingested seasonally, however I am suspicious that we would not benefit from a year round consumption of blueberries due to the potential inflammatory effects, and all the other good stuff in them.

I am a scientist however and I would love to have my assumptions proved wrong :)

Interesting question.

Personally, I am tyring not over-analyze or over-regiment my diet, so the only seasonal adjusment I think I would make comes down what veggies are in season at the farmer's market.

It's a good point, though.