This article is from the Big Folks Health FAQ, by email@example.com (Sharon Curtis) with numerous contributions by others.
There are two main types of arthritis, rheumatoid arthritis and
osteoarthritis. Osteoarthritis is joint-specific, and involves damage
to the cartilage of the joint and inflammation at that site,
along with pain, stiffness, yucky grinding noises and sensations,
and the like.
There is a correlation between being fat and being arthritic. People
do have a tendency to gain weight after getting arthritis, and conversely,
there are several long-term studies which show that fat people are more
likely to go on to develop arthritis, after starting out healthy.
Arthritis of the knee is the only disease that can be conclusively linked
to increased weight per se.
Obesity is positively correlated with osteoarthritis, weight-bearing
and non-weight-bearing joints [VVVV]. It is not known whether obesity is
a risk factor, or whether there is an unestablished risk factor
affecting both [Fel+].