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The Question of Seasonality in Human Health and Nutrition

Posted By Mark Sisson On March 25, 2010 @ 9:32 am In Primal Health | 93 Comments

How important is seasonality in our understanding of human health? In last week’s nuts [7] post, I referred to the seasonality and intermittence of nut availability [8] in the wild, implying that because they weren’t available to our ancestors on a year-round basis, excessive daily nut consumption may not be in our best interest. Regular, consistent, high-volume nut ingestion may not make sense in the light of human evolution, but does that necessarily make eating nuts – or, really, any food – in anthropologically unrealistic amounts detrimental to our health?

What about seasonal behavioral patterns, or seasonality of access to sunlight [9]? Does it make sense to view our every move, our every tradition, in the light of the seasons? What do we mean by “seasons,” anyway – aren’t the seasons different depending on several factors, like proximity to the equator? Or is there an ideal seasonal cycle all humans should strive to follow, regardless of location or background?

To establish whether or not an ideal human seasonality even exists, it would help to establish what we know about our earliest stomping grounds. What was the climate like where and when we evolved? What were the seasons like? Humans evolved in East Africa, with modern Homo sapiens first appearing around 200-250 thousand years ago. It’s popular to suggest we evolved in a stable, constant Edenic landscape: lush forests, grasslands teeming with wild game and edible vegetation, steady rainfall, predictable seasons. The reality wasn’t so neat and smooth though (is it ever?). In fact, the region has seen major topographical and climate changes over the ages, beginning with the clash of the Indian and Asian tectonic plates 40 million years ago, which set into motion both the uplift of the Tibetan plateau and massive volcanic activity in East Africa. The growing Tibetan plateau deflected moist air away from East Africa, while the volcanic activity coincided with rifting in Ethiopia. The newly formed rift valley and accompanying rift shoulders, or mountain ranges, led to even more deflection of moist air, and what began as a uniformly flat plain covered in rainforest became a landscape of plateaus, mountains, and valleys featuring both cloud forests and desert scrubs.

Temperature was fairly constant, tending toward the warmer side of things, but the seasons were characterized by intense bouts of rain and drought. A wet period might last thousands of years, only to be followed by centuries of brutal drought. Enormous lakes could dry up in a hundred years (a blink of an eye), rapidly changing an established people’s way of life and spurring innovation. Seasonal cycles no doubt followed the wet/dry dynamic, and this is where and how we evolved – in a constant (on the large scale) state of flux. It was a tumultuous, highly variant environment, and some anthropologists think it had the effect of producing the most adaptable species on the planet: us. Good thing, too, because if we were going to successfully migrate to every corner of the globe, we had to be prepared to make quick adaptations.

Based on that ability to adapt, I lean toward the absence of a cut-and-dry seasonal mentality that applies to all humans. I mean, just look around. We see and hear examples of humans surviving, even thriving, in any locale, under any climate, and exposed to any environmental pressure. We live where it rains 3/4 of the year, and we live in bone-dry, arid deserts.

Before I sat down to write this, I was planning a fairly basic examination of seasonal foods. Once I began digging around, things became a little more complicated (as they always do). I think I’d be shortchanging the topic and over simplifying a complex issue if I stuck with what I imagined the script to look like. It’s not so much that there isn’t a single seasonality that we can all adhere to; it’s that there are multiple cycles that “work” with our respective physiologies. That’s the whole point of being human, really! We adapt, we conform, and we mold.

I have a feeling this will be a broad topic, and I won’t be able to cover everything, but I’ll try in a series of upcoming articles: The relationship between Vitamin D and fructose consumption, spring and winter fats, egg, meat, and tuber availability, intermittent fasting, the remarkable similarities between the climate of the modern Hiwi tribe of Venezuela and that of our early human ancestors in East Africa (found the free full text of a fascinating study) and what they all indicate about our ancestral seasonal diet.

In the meantime, leave me your thoughts in the comments section, and stay tuned!

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