The problem is acidity. The digestion is acid, and the acidity is normally neutralised in the colon, with calcium. Alcaline forming food (plant products) reduce acidity in the digestion, while animal products increase acidity. After take-down I could not cope with animal products at all and went back to the plant based diet. I ran four trials with animal products and found that the acidity with animal products took one to four days to kick in and took up to two weeks to come back to a level that I could cope with. The ph levels also vary for other reasons. So for us, alcaline forming food should be better, and for me they are. I also avoid acid fruit. I don't eat anything with a ph below six.