This is an (I think short) story. I think I read it in some story compilation.
This human is in the far future and by his time evolution has caused people to become enormously fat (large and nearly spherical), so much that they are unable to support their own weight or make use of their limbs. Instead, robots tend to their every need. Btw, I'm not sure, but maybe only one human has remained by that time.
The fat human entertains himself by doing mental time tourism - he enters the mind of people from our present. The protagonist is one such person who has his mind entered. He can feel it.
The story in question was partially a love story I think.