If you're following good nutritional practices and minimizing the intake of high-GI carbs (sans your PWO periodization), a cheat day filled with lots of high-GI carbs (rice, pasta, potatoes, cereal, bread, simple sugars), moderate protein, and low fat (think ADA guidelines), you can "replenish" your glycogen stores. For example, I eat ~ 80g of Carbs on non-training days, coming from neglible sources (soy sauce etc.), lots of fibrous veggies, and a piece of fruit or two, or perhaps some oatmeal. All of these carbs fall below 50 on the GI scale, and are equally low on the insulin index. My training day intake bumps this up to around 125 - 150g of Carbs. I add in a 2:1 ratio of high-GI carbs and protein immediately PWO, and then consume a 1:1 ratio of low-GI carbs, protein, and some fats (a 40:30:30) split an hour or so afterwards.
Come the weekend, I take in around 350 - 400g of Carbs, very low fat (30 or 40g maximum), and moderate protein. My vascularity and overall density explodes, and I experience very little fat gain, if I time it correctly. It took me a long time to figure out just how much I need to eat and in what time period. I consume the 350-400g of carbs over a six hour period, and just consistently refill with grains. This lets me get my "fix" (I love Asian food, but white rice and maintaining a lot of muscle while staying lean for a poor-carb metabolizing individual such as myself, are somewhat mutually exclusive) and maintain good body composition.
I personally respond poorly to balls out cheats. My body spills over into storing the nutrients as fat far too quickly. Just note, the "rev up the metabolism with the cheat meal" thing is bunk. I know Lyle McDonald preaches his leptin story, but I think for someone who isn't doing an insane CKD or UD 2.0 type diet, the balls out cheat tends to throw you off the tracks and derail individuals too much. Find out what works for you. I keep my cheat "periods" limited to around 2x a month. On the weekends where I don't "cheat," I refeed and add perhaps an additional 500 - 750 calories to my diet, consistently of low-GI carbs, proteins, and good fats.
I find my response to cheats directly correlates to how well I followed my nutritional guidelines during the week. When I was first experimenting with this, my cheats would turn into weekend binges. Not good
I'd then starve myself during the week, and then boom, cheat again the following weekend. Don't fall into that pattern like I did.
Good luck to you. And take care.
