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