If you want to achieve a nice swimmer body with lean, defined muscles and nice abs, go with keto and fast for one day every week. You can do 16 hours, 24 hours, or 32 hours if you like, just check with a doctor first to make sure you’re healthy enough to do so. Keep in mind that ketosis basically means your body is eating itself, in the form of excess fat being burned and used as fuel. If you’re already skinny, you risk eating your own muscles, up to and including your heart muscles (not good!). So anyway, if you’re happy looking lean and refined, do keto and combine that with calisthenics. If you want to look like the hulk, you’ll actually need to eat more and lift progressively heavier weights. I can’t give you much advice there since I prefer looking lean to eating a shit ton of calories every day. Bonus bit: fasting gets easier and easier the more you do it. You may have trouble sleeping at first, but that goes away eventually. As for hunger pangs, just drink water and they go away within the hour. Coolest thing I learned from fasting is that it completely resets your cravings. I used to be addicted to sweets, but now I have no interest. #Consult with a doctor/dietitian before making radical changes to your diet and exercise plans.