I Have Been On A Medifast Diet Plan For The

I have been on a Medifast diet plan for the last six months and have lost 45 lbs. I feel great except the fact that for about the last 4 weeks I've had Urgent Grainy, Watery stools several times a day after I eat a meal which is 6 small meals a day. For the fist five months, I had the perfect "S" shaped stools!! Seems like something has changed in my body. I know a lot of the Medifast products are soy based. Any ideas?