If you were 178cm and only 68kg so you were really skinny or skinny fat. I am going weight training to the gym regularly (currently 4 times a week, but will increase to 6 times as I'm planning to change my routine and use a different split) and also I am 178cm height and my weight is 75kg. Also I am really lean with a very low body fat (I think around 10%). So if you could achieve that it would give you only positive effect for your TT play. If you gained weight to 75kg but gained not only muscle but also fat (gaining only muscle while bulking is pretty hard to achieve), it wouldn't have any negative effect to your TT as well, as being 75kg at 178 is also really ok. And, as everyone mentioned in multiple examples, table tennis is not about muscles or body mass or age. It's everything except that
To gain the levels of muscle that would have a negative effect for playing table tennis, you have to go into some very serious bodybuilding (for example had a weight of a 100kg for your height while still being on normal body fat levels). But if you somehow got there, it would definitely decrease your TT performance.
by the way, as this post is a couple of years old, did you achieve your goals?
that's not how it should be done. Basically your diet should be calculated in the following way:
-calculate the amount of calories you need to consume daily (depending on your physical activity, age, height, body composition and your goal -maintain, gain muscle mass, lose fat)
-then (depending on your goals) adjust macros: firstly the amount of protein needed (a lot more if you are on a weight loss diet to preserve your lean muscle mass), then the amount of good fats needed which is constant and independent on your goals, the remaining calories can be consumed as carbs.
So basically you shouldn't use as little fats as possible as they are vital for your body function.. but use no less than the minimum healthy amount for you and then add carbs if you are bulking and cut them if you want to lose fat
