Here is the full list of all 30 Cat on a Diet achievements. It takes around 6-8 hours to unlock all of the achievements on Windows.
Unlock 65 Costumes
Hit Laser 50 times
Teleport 50 times
Unlock 50 costumes
Complete All Bonus Levels
Complete World 4
Hit 25 spikes
Cut 25 baskets
Use Catapult 25 times
Complete World 3
Destroy 50 Uranium tiles
Collect 512 Muffins
Hit the Ground 50 times
Change Gravity 50 times
Change Gravity 25 times in one level
Complete World 2
Unscrew 100 screws
Travel in a basket 25 times
Eat 25 chewing gum
Complete World 1
Use motor 25 times
Collect 256 Muffins
Collect 128 Muffins
Slash 200 wooden tiles
Complete a level with no Muffins collected
Play for 10 minutes
Collect 64 Muffins
Complete your first level
Collect 1024 Muffins
Unlock 80 Costumes