However, I believe that losing a large amount of weight (and keeping it off) is more about: 10% exercise, 40% nutrition, 50% facing what you've been avoiding. This is what is commonly branded as behavior modification and/or change; but I want to take it farther and delve deeper into the specifics.
Regarding disease in this matter. Disease complicates, but it does not stop these efforts.
~ It is a cumulative affect not and immediate result. ~
Simply getting up and reducing your sedentary lifestyle can work wonders. Then image what could happen if you added purposefully exercise bouts via specific cardiovascular efforts, strength efforts, flexibility challenges, or all of the above.
Humans are amazing and most of us only use 10% or our brains. What would have if we really devoted 10% of our efforts to fitness - it is amazing what changes this can bring. Simply making plans to be slightly more active during the day in some way would go very far to making some big changes.
If you put crappy fuel into a performance vehicle, in a very short time the performance vehicle would start to run like a rusty Volvo from the 60's with broken windshield wipers. Likewise, if you eat poorly or imbalanced you break, swell, barely inching forward, with very little ability to assist others around you - let alone yourself.
The absolute biggest issue I see in this area as a fitness professional is inadequate hydration, crazy high sugar intake, and sodium intake that is off the charts.
50% Facing What You've Been Avoiding
Laziness (a.k.a, disbelief).
Memories of what "used to be".
Being motivational hampered by too much futuristic thinking.
The root of many of the problems I see clients (and myself) facing, seem to stem from one of the following:
Lack of perceived social acceptance.
Lack of commitment or motivation = no follow through.
Poor or unrealistic goal making.
Persistent negative self talk.
Unexplored and unresolved issues.
Not using support resources.
Now, of course there are many serious medical issues that some of this doesn't apply to. However, the greatest of all interruptions that I have professionally seen on this topic, have not been from major health issues. I strongly encourage those in the pursuit of serious weight-loss, to also companion their efforts with a mental health professional, support group, or a highly supportive confidant, while perusing such "weighty" matters.