Seasonal variation in nutrients

I live in a place with four seasons, and I love it when the leaves start changing and I can buy recently-pressed apple juice at the grocery store. Squash, apples, and grapes are fresh and relatively inexpensive in the fall. It's one of the tastiest times of year.

Then comes winter with savory stews using root crops, meat, and grain. And I'm always happy to see spring and summer again, with fresh produce coming back to the supermarkets as it grows and ripens. The different foods of each season help me vary my diet, which I've come to realize is very important for two reasons:

1) Homeostasis, or "the ability to maintain a constant internal environment in response to environmental changes." (http://biology.about.com/od/biologydictionary/g/homeostasis.htm) Our bodies do visible, obvious things to maintain constancy in many circumstances. A common example used in biology lessons about homeostasis in humans covers how we sweat to stay cool and shiver to keep warm. But we also do less obvious things such as downregulate production of certain molecules when there is extended exposure to a nutrient or stimulant that interacts with that molecule. (E.g., http://jn.nutrition.org/content/128/10/1829.full and https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3773689)

Periodic rotation of the foods we eat can prevent unintentional long-term overdosing on any one nutrient. As part of my religion, I also go without food and drink (except water) for approximately 24 hours once each month, which helps me have short, scheduled breaks from pretty much every nutrient. As long as I don't gorge on chocolate cake right after ending the fast, it seems to be a good thing for my health, and there are studies supporting the health benefits of periodic breaks from food (E.g, https://www.sciencedaily.com/releases/2011/04/110403090259.htm).

2) Extreme eating is frequently problematic, and varying foods with the seasons helps avoid it. I don't know if extreme eating is more often a cause or a symptom of mental illness, but my observations over the past decade have been that extreme eating habits and mental illness seem to go together. What is extreme eating? I think it encompasses any kind of eating philosophy that overrides the fundamental human need to be well-nourished. If one's eating philosophy causes malnourishment or obvious physical symptoms of illness, that's a sign that it's extreme. Nutritionists keep repeating mantras about "healthy, varied diets" because too much of a good thing often turns into a bad thing.

Too much avoidance of perceived "bad" foods can also be extreme eating. There's a name for that, "orthorexia nervosa:"

The term was introduced in 1997 by American physician Steven Bratman, M.D., who suggests that in some susceptible people, dietary restrictions intended to promote health may paradoxically lead to unhealthy consequences, such as social isolation, anxiety, loss of ability to eat in a natural, intuitive manner, reduced interest in the full range of other healthy human activities, and, in rare cases, severe malnutrition or even death.

https://en.wikipedia.org/wiki/Orthorexia_nervosa (accessed October 3, 2016)

I'm mindful of the need to avoid my nutrition research giving my children orthorexia. For instance, I'm no fan of folic acid or cyanocobalamin, and they know it. But I still buy foods with small amounts of them for my children and myself sometimes because I have seen no evidence of small amounts causing harm to our family specifically or in scientific studies. At social events, our family eats whatever tasty snacks appeal to them...even Oreos, which are definitely just a "sometimes treat." Human bodies have mechanisms to detoxify and excrete harmful substances, and we can generally rely on those mechanisms as long as we don't overwhelm them with large quantities of harmful substances or have genetic susceptibilities to those substances.