Thanks for contacting healthcare magic. After taking meal some amount of bowel movement is common physiologic phenomenon. In stressful condition, bowel movement may be increase. In irritable bowel syndrom, abdominal cramps is present. You mention that after taking food immediately bowel movement is started that indicate crohn s disease also. In Crohn s disease is diagnose by endoscopy. Diarrhea, pain,blood in stool,weight loss are also present in crohn s disease. For gain a weght eat high fiber diet like lead,black beans,like beans,broccoli,rasberry etc... Take multigrain in diet. Eat fress fruit and green vegetables. Drink whole milk with banana. Don t Take stress too much. Eat healthy foods and avoid junk foods. Take care. Thanks.