Is it common to get muscle spams all the time when on extreme diet ?

May be: If you are on extreme diet and lack potassium or calcium you can have muscle spasms.

Is possible: I agree with dr. Tran, & would add dehydration to the list of relatively common concerns that can develop with certain extreme diets. Dehydration can lead to a variety of problems including muscle cramps/spasms. If you need to loose weight & are trying-good job, but if doing it in an extreme manner, please be sure you're doing it with medically supervision so you can have proper monitoring.