Hello sudden weight loss in this age group is a matter of concern dear this could be due to any of following indigestion or mal absorption syndrome Worm infestation Tuberculosis or HIV infection in my opinion you should consult a gastroenterologist for examination and a battery of tests like blood profile and a colonoscopy or endoscopy mean while ask him to have good balanced food with multivitamin supplements plenty of fresh fruits and vegetables well cooked meat and meat products avoid excessive fried or junk food or carbonated drinks smoking and alcohol to be given up hope this helps him best wishes