Thanks for using Healthcaremagic,
Your problem is blood in stool
,this can occur due to many causes like infection local cause piles, fissure etc.
If you are losing weight specially with the help of machines they cause lot of perspiration and if proper water intake is not there it may lead to dehydration
can make stool hard and there can be trauma in the rectum
and cause bleeding.
You should avoid constipation and take good high fiber diet including fresh fruits and whole cereals.
I would suggest you to visit a surgeon who will examine internally and do proctoscopy to find any source of bleeding if there it can be treated depending on cause with appropriate therapy.
It is good that you continue to lose weight by exercise and consuming less calories food.
Keep yourself hydrated with adequate intake of water.
Hope this helps.
Dr.Akhilesh Dubey M.D