I feel like this question is very troll but my guess is for less weight to hold them down....
They are natural pain and stress relievers and with excerise it helps the heart pump blood with less effort.
I couldn't find that much but I found the same question as yours and this is another person comment. :3 hopefully that help :D
A diet that can lower your stress looks like something with a lot of fruits and vegis. Making sure you get a least one hour of exercise a day. Plus drinking tons of water and a some juices. Foods I'd consider would be pineapples, strawberries, bananas, cucumbers, carrots, and etc.
You may fall and get hurt can be too the weight of the backpack
