Let's use cheese for an example.
For the past 50 or so years, we've been told that cheese isn't good for you. Cheese his high in fat and cholesterol and we've been conditioned to believe that too much of it leads to obesity and heart problems. There is a kernel of truth to that. Yes, cheese is high in fat. If you're trying to lose weight, you'd be smart to severely curb your cheese intake. Losing weight is about eliminating surplus sources of energy (fat) on the body. Plus, most Americans drastically over consume cheese when they eat it.
Blacklisting cheese as an unhealthy food, something bad to be avoided by everyone, isn't right either. If someone ever tells you that, then I suggest bringing up the ancient Greeks.
A couple of years ago, I was enlightened by Randy Roach's book, "Muscle, Smoke and Mirrors," that Greek athlete's diet included generous quantities of, among other things, Feta. In fact, it may have been one of their main sources of protein. One thing that hasn't changed much since civilization dawned in Europe is the lack of grazing space makes makes it difficult to raise animals for meat in any significant quantity. Thus, meat has always been more expensive. So, food items like yogurt and cheese became the principle sources of animal protein for much of the population. After all, you could get more protein from the animal over it's lifetime and it kept longer. It was believed that athletes and soldiers in Greece probably got more of it than the common people. Obviously, the ancient Greeks weren't getting fat off of their cheese consumption. In fact, you could truthfully say that the ancient Greeks may have been one of the fittest cultures in world history! So, it's entirely possible to eat cheese as part of a healthy diet. While it may be high in fat, it's also a very good source of protein, calcium, and B-vitamins (from the fermentation). It's GI is so low is almost immeasurable, so it helps regulate blood sugar.
So, this food is a shining example of the fallacy of putting, "good" and "bad" labels on foods. How much of it you should consume will vary depending on your physical circumstances. How active are you? Do you have weight to lose? Are you trying to gain muscle mass? Once again, you need to take your individual needs into consideration when planning out what you eat.
When I eat cheese, it's usually one of two ways. I like it in an omlette, first thing in the morning. I'll usually put in one ounce (yes, I measured it!) with three eggs and some mixed veggies. For lent, I got into the habit of eating grilled cheese (asiago, about two ounces)for dinner along with a generous-sized salad or a bowl of shredded red cabbage. I generally like to eat cheese in the mornings or the afternoons. If I have it with dinner, I try to keep the entire dinner low carb. Most of us who know will agree that you don't want to eat a high-fat, high carb meal. It's a sure way to feel slow, heavy and tired for hours afterward.
Regardless of whether you're in good shape or trying to lose some weight, by all means avoid the WAAAY over-processed cheeses. This stuff is garbage and should be avoided like the plague. Stick to the stuff that has ingredients that you can identify (well, except for the bacteria they're using to ferment the stuff) and the stuff that's not dyed. To the best of my knowledge, there isn't a cheese on the planet that should be bright orange! Find some local sources of cheese. There are a lot of hard-working farmers putting out some great cheeses these days. Healthier too.
As always, if you're unsure if you should or shouldn't be eating this, or any other food, my suggestion to you is to experiment. Eat the suspect food in question, wait 1-2 hours (or however long you need to wait before working out), train and see how you feel. Good food will always fuel you up properly for the work. The junk will leave you slow, weak and feeling like shit mid-way through the workout. I haven't found a better test yet of what you should or shouldn't be eating.
"Grilled cheese fucking rules and should be eaten three to four times a day as I've found a direct correlation between being awesome and the uninhibited consumption of grilled cheese."