I read an article about carbohydrates and was wondering which I should consume before starting an exercise.
Simple carbohydrates or the complex ones? And does it really matter or anything goes? Does it depend on which are fastest to get digested?
What type of exercise? If it's short burst exercise such as the anaerobic exercise of body building, then simple carbohydrates are better: baked potato with cheese. For long aerobic exercise such as marathon running, slow burning complex carbohydrates work best - pitta breads, pasta.
This book goes into a lot more detail:
Whether to eat high GI or low GI foods pre-exercise has long been a controversial area. Many experts recommend a low GI meal based on the idea that such a meal would supply sustained energy during exercise. Indeed, a number of well-designed studies carried out at the University of Sydney have supported this recommendation. For example, the researchers found that when a group of cyclists ate a low GI pre-exercise meal of lentils (GI = 29) 1 hour before exercise, they managed to keep going 20 minutes longer than when they consumed high GI foods (glucose drinks, GI = 100; or baked potatoes, GI = 85) (Thomas et al., 1991)
[...] This isn't necessarily rule of thumb as other studies have found that the GI of the pre-exercise meal has little effect on performance, with cyclists managing to keep going for the same duration whether they ate lentils or potatoes (Febbraio & Stewart, 1996).
A UK study confirmed that athletes burn more fat during exercise following a low GI meal of bran cereal, fruit and milk compared with a high GI meal of cornflakes, white break, jam and sports drink (Wu et al., 2003). The benefits kick in early during exercise, the difference in fat oxidation is apparent even after 15 minutes.
As you're not a professional athlete (I'm guessing), or even if you were, it's really whatever works best for your body based on the sport and the food which takes a few months of trial and error.
When looking at the type of exercises you are planning, you don't have as high a demand for carbohydrates as someone who is long distance running or weightlifting. The type of carbs really has to depend on when you intend to ingest them. I've been weightlifting for a while, and I really don't need the spike that Chris S's answer suggests. In fact, for my purposes all I need is energy which can come from carbs or fat.
In general, a slow burning carb is better for exercise. Slow burning carbs take up to 12 hours to properly digest, so it should be eaten well in advance of your exercise. This is why runners tend to carbo-load the night before they run and run in the morning. That morning they will have something that is higher in protein.
The bottom line is that both walking and yoga is in no danger of depleting your normal energy stores unless you've been fasting all day before you exercise. You can walk for hours on end without needing additional carbohydrates. Jogging is a little more demanding, but still you would be OK with replenishing the carbohydrates after you work out rather than before.
Also, it is safe to say that the highly processed carbs that you find in candy and sugar sodas (not diet) are too easily absorbed by the body. While they can grant you a quick energy boost for a few minutes, when your body is done with this unnaturally high level of nervous energy it crashes and leaves you with less energy than before you ate them. In short your insulin processed too much sugar and temporarily left you a little hypoglycemic. No carbs should be simpler than whole fruit (not dried) or potatoes. Your body is able to deal with these carbs and not overcompensate.