Starting messing with my diet in an effort to improve my health about a month ago.
First thing I did was to start taking Vitamin D more regularly (400 UI per day), around the same time I starting having Huel. I felt great after a few days, however noticed I was going to the toilet less often. I attributed this to the fact huel is lower in mass to normal food. However I started getting worried after about 2 weeks as my constipation was just getting worse. Then I had the really bad luck of my doctor calling me up and telling me I was vitamin D deficient, so I tripled my dose (to 1000 UI per day)! I stopped taking Huel, not thinking the vitamin D could be an issue. But it was only after 2 weeks of bad constipation that I realised it was the vitamin D causing it - stopped taking it and felt a massive relief after only one day.
I think what happened is the vitamin D was reducing the amount of magnesium in my gut, which is essential for muscle relaxation. I might have a go with Huel again and possibly supplement with magnesium although the amount of vitamin D in Huel should be fine as long as I don’t take any supplements. The other theory is that the vitamin D was upping the amount of calcium in my gut, which can also cause constipation.
Hope this can help anyone suffering from Huel or vitamin D related constipation.