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 80 Costumes
Hit 25 spikes
Cut 25 baskets
Complete All Bonus Levels
Complete World 4
Unlock 65 Costumes
Use Catapult 25 times
Complete World 3
Teleport 50 times
Collect 1024 Muffins
Hit Laser 50 times
Unlock 50 costumes
Destroy 50 Uranium tiles
Change Gravity 50 times
Change Gravity 25 times in one level
Complete World 2
Travel in a basket 25 times
Unscrew 100 screws
Collect 512 Muffins
Complete World 1
Hit the Ground 50 times
Eat 25 chewing gum
Use motor 25 times
Collect 256 Muffins
Complete a level with no Muffins collected
Collect 128 Muffins
Play for 10 minutes
Slash 200 wooden tiles
Collect 64 Muffins
Complete your first level