Diarrhea when dieting is usually from a sudden increase in fiber, along with your digestive system adjusting to stuff that might be a bit more "effort" to digest than the average industrially refined food products. Things like eating more fruit and vegetables, switching from white to brown bread, or maybe replacing a snack cookie with a nut- or grain bar could already be having a large effect on your digestion.
The diarrhea you describe also sounds a bit like a symptom common for people who follow an "intermittent fasting" type diet, where you eat normal for some days and very little on other days. Controlling hunger through increased fluid intake will do that; you can find more info about this if you look up intermittent fasting.
You could try to assist your digestive system with some OTC probiotics; those will be beneficial in any case, restore your intestinal bacteria after bouts of diarrhea, and if this diarrhea were to be caused by a mild infection or something else unrelated to your new diet, they should also help.
I don't think it is from eating less. But maybe it is the fiber of the salad when eating less. Not sure. I know things like cabbage are notorious for causing diarrhea. Anyway, has this resolved?