thank you for your query in healthcaremagic.com..... well your height is 174 cm and you weigh 57 kg....so your BMI or body mass index comes as 18.83 which is normal...the normal BMI range is from 18.5-24.99 and your weight should be in between 56 to 75 kg.... you have also said that your ancestors have lean and thin built...so it is quite normal for you.... anyways if you still want to gain weight, you can try the following- eat healthy, eat three heavy meals a day but dont eat fatty food more, though it increases weight, the risks are more... see a DIETITIAN for a diet chart which you can follow... hope this was helpful.... regards