Let's investigate these questions a little further...
When trying to determine whether or not a food is good for us, this is the first question to ask.
The easiest way is to look at the qualities of the food in question, and compare those with the qualities we are seeking to increase or reduce within ourself. For example, let's say I'm experiencing anxiety. According to Ayurveda, the ancient healing tradition of India, anxiety is seen as an excess of air and ether elements, and has the qualities of being light, dry, cold, mobile, and rough. In order to balance the anxiety, we need foods that have opposite qualities of grounding, oily, warm, stable, and smooth--foods such as good quality oils and roasted root vegetables.
One big mistake I realized I was making when I first discovered Ayurveda was that I was eating too much raw food. I tend towards feeling ungrounded, dry, and cold, and the raw foods I was eating only made things worse. This is because most raw food is also light, dry, and cold ... and like increases like. Once I changed my diet and began eating more grounding, cooked vegetables and whole grains, my digestion improved (along with my sense of feeling grounded, warm, and stable).
When we eat is just as important as what we eat. Our digestive fire is reflected by the sun. When the sun is highest in the sky, at noon, our digestive fire is at it's strongest. This is why it's optimal to eat our biggest meal in the middle of the day. Eating a big heavy meal first thing in the morning, or late at night will squelch our digestive fire, and the food won't be properly broken down.
Another factor we can look at when asking "when" to eat something is the season. For instance, eating ice cream during the winter, the coldest time of year, will increase the cold quality in our body, which can lead to an excess of mucous or congestion. However, eating ice cream in the summer might not be so bad for us (in moderation, of course). Same goes for eating hot spicy food in the summer ... it will increase the heat in your body, and may lead to feeling "hot-headed," agitated, aggressive, or angry. But in the winter, it might be just what your body needs. Fortunately, nature tells us which foods are balancing for which seasons through locally grown produce.
Lastly, we must ask how much of something is appropriate for our body. We want to favor foods that will promote balance, and reduce foods that might aggravate an imbalance. But it doesn't mean we need to completely eliminate "imbalancing" foods, or only eat "balancing" foods. Moderation is key. For example, I didn't completely eliminate raw foods from my diet. Instead, I've reduced the quantity from what I was eating, and now I only eat raw foods during lunch when my digestive fire is at its strongest.
There are lots of ways to "antidote" certain foods as well...for example, if I was going to eat spicy food in the summer, I'd be sure to add lots of lime juice and cilantro, which are both cooling and help to mitigate the heating effects of the spices. This is another way we can moderate the qualities of the foods we are eating in order to maintain balance and health.
What do you think? Have you tried a diet approach that didn't work for you? I'd love to hear your thoughts and experiences in the comments below!