I feel that this is a pretty significant post, tying some things together that I haven't seen anywhere else. Earlier, I was reading through this paper , that speculates that Vitamin D deficiency is the cause of common obesity. I think the paper is on the right track, but it doesn't go far enough.
Before I make my argument, I need to make some other points. If you look at different variables, you see seasonal variations. First, there is a seasonal variation to inflammation . Second, there is a seasonal variation for testosterone in men. Third, there is a seasonal variation in body fat . And of course, there is a seasonal variation in Vitamin D status , barring supplementation. In all these studies, the negative results are highest in the winter and lowest in the summer.
In the paper I initially cited above, the author feels that a lack of Vitamin D is connected to all of these conditions. The idea is that the body senses less sunlight via internal Vitamin D levels and shifts into winter metabolism. Winter metabolism is equivalent to the metabolic sydrome. Therefore, obesity results when a person is in a continual winter metabolism.
I think this argument is mostly correct, but it doesn't go far enough. If you look at diet and inflammation, you start to see some other connections. Specific types of fruit, like citrus fruit and berries, lower inflammation. Of course, fruit is only naturally available in the summer time.
Next, you see that flavonoids and phytochemicals in plant food also lower inflammation ( here and here ). So what causes the development of flavonoids and phytochemicals in plant food? Sunlight (see here and here ).
Here's my thoughts: in Paleolithic times, less sunlight in the autumn triggered the winter metabolism. This led to a whole host of things - accumulation of body fat, declining hormone levels, increased inflammation, etc. These are all things that are associated with the modern metabolic syndrome.
In the springtime, these conditions began to naturally reverse themselves. However, this was due to an increase in sunlight AND an increase in anti-inflammatory plant foods that became available.
You can even take this further and look at how certain plant foods protect the skin from sun damage. This new study shows that foods containing phytochemcials and polyphenols (which are generated from sunlight) appear to protect human skin from sun damage.
In modern times, people can get trapped in a permanent winter metabolism due to lack of sun exposure and lack of plant food in their diet. What is supposed to be a transient state of the metabolism for a few months becomes a permanent condition. You also have children now being born with a "winter metabolism" due to poor maternal diets.
To escape this cycle, people need sun exposure and these plant foods that contain flavonoids and phytochemicals. As I talked about in a previous post , I'm not sure if Vitamin D supplements are equivalent to sun exposure. In the wintertime, people may want to use phototherapy or even tanning beds to increase Vitamin D levels. Combining this with anti-inflammatory plant foods may allow a person to break out of the metabolic syndrome.