As said it varies from country to country and from person to person, the profession, ailments, weather conditions, working style..... do have there own impacts on food habits.For ex fishermen eat early morning before entering the sea, those who work on shift basis eat according to their duty timings. Eating habits of elderly person are different from a pregnant or breastfeeding women.... The executive of a company and labour have different schedule of meals. So it can't be specifically pointed out but yes three times a day meals is by and large an acceptance in human society. Whatever may be, when you eat, eat two morsels less as to keep yourself healthy and to take care of those who are poor, for them the question is not how many meals a day but how to get a stomachful meal, at least once a day.