The Japanese say “Itadakimasu” before eating and “Gochisousama” after eating. These are often translated into “let’s eat” and “thanks for the delicious meal” but not perfectly translated into English yet.
Because these words not only are just greetings but also express their appreciation for the nature’s blessings, those who have cultivated them, and those who have prepared the meal.
The concept came from the Shinto, Japanese unique religion, which does not exist out of Japan.
As you can see, their behavior while saying “Itadakimasu” looks like exactly the same as at shrines. They put both palms together in both cases.
The Japanese are originally agricultural people. They prayed the nature for good rice harvest in spring and appreciated the nature for the results in autumn.
They believed that gods resided in every living things in the natures and that the invisible gods helped them with good blessings.
So people began dedicating the Sake made from rice (the nature’s blessing) to the gods at shrines. This is the origin of Japanese autumn festivals.
All the Japanese have been brought up at home and schools to say “Itadakimasu” and “Gochisousama” since they were born. It's a very common customs for them.
This practice has also affected their eating manners. You can neither walk nor make noises during your prayer and appreciation.
You will sit and keep quiet. Eating meals while walking in Japan is treated as a breach of the manners for this reason. So it is considered bad manners.
As Western food is now popular in our daily lives, there are more people who don’t mind eating while walking, especially in the young generation these days.
Most of the elderly, however, still love to sit and eat Western food in the good manners.