As I try to eat right, one of the questions that comes up; "Shouldn't I always buy and eat organic?" Beyond my admonition to try not to be so perfect that you stress out or abandon the good in search of the perfect, there are still good reasons to sometimes buy organic, and sometimes just not worry about it.
There are a number of advantages touted for organic products. Some of these I very much understand and take advantage of, some of them are being questioned in recent studies, and some of them I don't much worry about.
Organic Plants Have More Nutrients
I think the jury's out on this one. In principle, growing food organically means the farm can't depend on chemicals and things to keep the plant healthy. This would imply that the nutrients to feed the plants would have to come from the soil, implying that the soil may need to be more rich than the soil where non-organic plants are grown. Studies on the subject seem to be split and probably depend mostly on who sponsored them.
Bottom line: I think this is probably true but probably not enough to go too far out of my way to buy organic.
Organic plants and animals
expose you to fewer chemicals
This is my primary reason to buy organic when I do. I use a relatively simple rule of thumb. If it is a food you are consuming the outside parts of, the parts that are exposed to most of the chemicals in question, then I try to buy organic. If not, then I don't feel I have to go out of my way to buy organic. For example, avocados -- I don't need to buy organic since I don't eat the skin. Another example, leaf lettuce -- I try to buy organic since the leaves are exposed to all the potentially toxic chemicals.
A good website for ideas on what you should and should not buy organic for this reason is ewg.org On the site they highlight their "Dirty Dozen" (the foods from which you will have the most exposure to chemicals and the ones you should buy organic) and their "Clean 15" (the foods that have the least exposure and the ones you probably don't have to worry about getting organic.)
Organic processed food
Using organic doesn't help you if it's highly processed food in the first place. You should avoid highly processed food and eat "real" food. Ignore the label "organic" on highly processed foods and avoid those foods altogether.
This is a tough one. All else being equal, I would probably choose non-GMO. I don't believe that GMO is inherently bad for us, just because it's GMO. I'm not "scared" of it just because it's genetically modified. We've been genetically modifying foods for 1,000s of years. We used to (and still do) genetically modify crops by selectively breeding them to get the characteristics we want. GMO isn't much different -- just a whole lot faster. The biggest problem with that is that the objective of the modifications is all about productivity, resistance to spoilage, palatability, etc. Health doesn't likely play a big role. That means these crops are bed to be ultra sweet, palatable, etc. and are likely less heathy for us. But that's already happened, long before GMO was an acronym. Read the book Wheat Belly to see the effect this had on the modern wheat we eat and what it does to us. (You can buy at at the sponsored link to the right and help to support this site.)
My biggest problem with GMOs is the way the big companies such as Monsanto are treating local farmers, suing them because their crops end up containing genetic material that is patented (something I think is totally crazy to begin with.) The contamination of those crops is likely due to natural processes like wind driving pollination from neighboring GMO crops.
I've certainly not covered every possible reason to buy organic food, but if all else is equal, I would definitely choose organic. If it's much more expensive or hard to find, and it's not one that I think would have a strong effect on health, I don't go too far out of my way.