Can sudden ibs-d be improved only by diet ?

IBS-D: That helps, surely. Many people use immodium(loperamide) to prevent diarrhea when working. Stress reduction techniques may help. Probiotics can be tried, bile acid binders, antidepressants, mast cell stabilizers, and 5 ASA. Check out this link for more info: http://www.mayoclinic.org/medical-professionals/clinical-updates/digestive-diseases/better-agents-needed-irritable-bowel-syndrome-diarrhea

Only if due to diet: IBS can stand for irritable bowel disease or inflammatory bowel disease- both of which can cause diarrhea. Diet does influence your gut both in a negative and positive way, but to effectively treat you need to know the underlying issue. "Sudden" changes are always concerning for infection, inflammation, or additional causes Probiotics may help. Care with GI strongly suggested.