What are your thoughts on chia seeds?
Nothing special. A concentrated source of omega 3's. You can include them in small amounts, a tb or two a day if you would like.
WhatAre they fattening ?
No one food is ever fattening. Dietary patterns and lifestyles are fattening and calorie dense foods are easy to overeat on.
WhatI can run further and faster with them,
No one food, that is truly a food, can make you run further and faster.
Whatbut I also want to lose more weight. I am currently 5 kg above my target weight of 65 kg.
Than you need to follow a dietary pattern that is focused on low calorie dense foods and be active.
I would recommend you review the hot topics on calorie density and also the principles of the MWL program.