If you think that aikido will help you to lose your overweight you are wrong. You have to change your life style, diet and this under control of certified dietician. So I see it as a first step. Then, you may consider starting very light running every day, also following advices qualified coach. Only after that, you can be back into the tatami, otherwise it will be huge disappointment and you will quite dojo forever.
Touche Szczepan Janczuk.
BTW, how do you pronunce Szczepan Janczuk. What sort of name is that? Greek? Russian? Croat?