I didn't hear it anywhere, actually. I found it completely by accident. I was attempting to lose weight and my mom had mentioned grapefruit was great because it will help cut appetite. I'm also diabetic and love citrus and after some fact checking I found out it has a pretty low carb value so it wouldn't affect my sugars a lot. I also had heard it's a good way to flush your system out of toxins (which is why you can't eat it when you're on certain meRAB because it flushes the medication out of your system), so I thought what the heck?
Anyway, I've been having a pretty bad attack since Christmas. Constipation every day a long with a lot of pain in my lower back because of spasms. Everything made it worse (including flax and tons of water and I had given up red meat, dairy, sweeteners, etc... nothing helped!). But, the morning after I had the grapefruit in the evening my attack just went away. It's been a month or so, but every day I have a great bowel movement that seems to "clean me out" (I know TMI!) and I've never felt this great for so long (usually I'll have a great few days and go back to being constipated and miserable).
I find the ruby red ones are the best. The pink ones are ok, but taste-wise and action wise, the red ones are amazing. If you can tolerate a bit of splenda, put a few sprinkles on top for a bit of sweetness.
Oh I did some internet research on grapefruit and IBS, and the only thing I could find was how grapefruit seed oil/extract can help. I'm assuming if the seed oil can help then the grapefruit can't hurt! I'm going to try some of the oil for an extra boost.
I know what works for some might not work for others, but I really hope this helps you as I know the misery IBS (esp with constipation) can cause!