Never noticed spinach causing me problems, not sure what lutein would do by itself to cause symptoms. There is a lot of fiber in these foods and that may be more an issue for people (for good or bad) than any particular chemical in them.Anyway, it is one of the chemicals in food that is part of the cell wall so is locked in place and when people say something came out the way it went down it is usually a plant with strong cell walls that do not dissolve in the GI tract.Cooking breaks things down. Sometimes that makes heat sensitive nutrients go away, but for other things (also lycopene in tomatoes) the cooking allows something to be released that would otherwise mostly pass
through.http://www.mskcc.org/mskcc/html/69286.cfm doesn't list any side effects so it isn't known to be a big cause of diarrhea for people.