1) Dude, it's SO CONFUSING. Tuna is good for you! No, too much tuna gives mercury poisoning! Do low-carb! Low-carb will kill you! Wtf.
2) I found it rewarding to cut to one drink a week and then do sodas & lime, tipping on the water like a normal drink. : ) Or be good all week and have a slice or two of pizza at the end of it. Sweets are no problem, but I effing love pizza.
3) This is something I don't understand that well either. Personally, I ran at a bit of a deficit, but not enough to create a fasting state. I mostly lost fat (based on body fat analyzers and the measurements I took), but I also lost weight overall. I *think* I put on a bit of strength, but I only lifted 1-2x weekly so I didn't see huge gains. I guess what I was saying is...you could healthily weigh 215 at your height and that body composition is more important than the scale number, so
start tracking body comp ASAP. Measure yourself & take pics! If you don't see the progress you want in 1-2 months, it's a good cue you need to adjust. (Like now! I think the problem is not enough Calories ---> your body is burning everything, prob not the finer details of your macros. Calculate what you need for maintenance and don't run a deficit in excess of like 500Cals.)
3/4) So...it depends on your goals and what you mean by performance?
If you were going to run a triathlon tomorrow (>90 min event), your body would
burn through the liver and muscle glycogen stores first, then it would need something else for ATP (usable energy). It turns to metabolizing other things, some of which take more steps to turn into usable energy. Eating a stick of butter (fat) during your triathlon is not going to be an efficient way to make ATP available. It's like having money in cash (glycogen stores), versus having to run to three different banks and stand in line and then transfer it and withdraw it...UGH. (That's my understanding). Sure, it's money, but what you have to get through to spend it is more complicated than pulling out a $10 bill.
Along with that story about the triathlon, what do you do once you've burned the glycogen stores and you still have 3 miles to go before you finish your tri? The body can absorb carbs at about 60g/hr, hence the replenishing with Gatorade that you see. You can keep burning efficiently that way. That's why lots of marathoners carry GESs, Clifbar Shot Blocks, etc. Also note, muscle glycogen storage ability will vary: for someone untrained, it could be 12g/kg muscle. For trained athletes, it could be 30g/kg muscle.
Think of it like this: carbs are the most efficient fuel. Based on how you train and eat, you create a certain capacity for storage. You want to FILL that supply up before an event (carb loading), then try to keep it replenished to keep your body running the best you can.
So my advice before the tennis tournament or a triathlon would
NOT be to limit carb intake to 100g/day - I don't care what your overall goals are; it's not going to
optimize performance during the actual event. However, in training/fat loss mode...I think it's OK to limit to a degree so that your body burns through the carbs (used up by the central nervous system, red blood cells, and brain alone!) and turns to another source next, such as fat. Does that make sense? You just don't want it to burn everything, which is what you force it to do by eating 2000 Calories as an active, male, 215lb, 6'4" guy. Haha.
I'm not a nutritionist or anything; I just find it highly interesting and have been working my way through my course. Will come back and update if I said anything erroneous and am open to correction from others.
Here are some articles that you might find interesting. I *love* this website; it's targeted towards people who want to work smarter, not harder. Kinda like here!
http://www.nerdfitness.com/blog/2015/02/05/how-fast-can-i-build-muscle-naturally/http://www.nerdfitness.com/blog/2015/02/02/just-how-fast-can-i-get-the-body-i-want/http://www.nerdfitness.com/blog/2015/06/18/your-most-popular-diet-questions-answered/ <-- Steve would probably recommend keeping carb intake the same and just upping overall Calories so you don't go into fasting mode. Me, I think sustained effort is the main key, and that keeping ~30% AMDR carbs is just fine for fat loss. But who am I, anyway...