I watch a couple things about diet carefully. I use the myFitnesspal app partly because it interfaces with my Garmin watch to take exercise into account as well, and partyly because it makes tracking easy as any food you can think of is in there - raw, homemade, restaurant, packaged you name it.
3-4 times a year I track for a week or two to see how I'm eating. I get a free pass on salt sort of (addisons disease) but check all the other stuff calories, fats, carbs, all that stuff. I also like a really good multi-vitamin with lots of micro nutrients. GNC Mega Men is one of my favourites.
There are things we don't get out of our diet and something that "fills in the cracks" of nutrition, and all the things like magnesium, iron, selenium, etc that you may not get in your diet I think is hugely important. Those things may come in your food - but it depends if they are in the ground your food is grown in.
As for eating in the heat - it takes circulation away from the skin and cooling where adding water gives you more cooling capacity through sweat. If you reallly want to feel hot on a hot day? Drink a couple cans of cola and then go outside to work.....the a. digestion and b. sugar will have you overheated in no time.
Did a lot of research on this when I was working on playing better golf because - all those things tie together. You need to eat when you burn a few thousand calories in a few hours, (I have played 2.5 hour rounds - walking) My fave was PB&J cut in quarters or a bite or two of a Clif bar every hole or two. Small amounts of easy to digest food not a hot dog at halfway. Hydration - you gotta get ahead to stay ahead. Because the loss of salt through sweat is critical (Addison's again) for me. I drink a ton of water the night before, and then add a Nuun to the bottle I drink before playing for added electrolytes.