Hi Michelle, that did happen with me. I was very fit, doing a lot of athletics and eating sort of right, adhering to what I thought was the right way to eat with not a lot of thought put into it. My active life kept me within reasonable weight bounds.
When the OA hit, I still kept up my activities (soccer, basketball, martial arts, weights, etc.) and thought that would be fine, but the weight started to pile on. I am not a small guy anyways so my frame hid the increase in weight until I could not deny it.
I was perplexed, since I was still doing all of the things as before, even more in some cases - I added a fitness boot camp as a misguided way to 'fix' my hip, which I thought was just muscular tightness issues. One thing that all of my teammates in the different sports noticed was that I was getting slower.
In my mind, I still was moving as quickly, but I think in all of my activities I started to slow down without thinking to avoid the increasing pain. I also started to get much more sedentary in my regular life. I owned a beauty spa with my ex-wife (wife then), and spent a lot of time doing carpentry, painting, climbing ladders, etc. Not the usual fare for a computer engineer during off hours. This became worse and I found myself avoiding doing work that I thought nothing of before.
All of this, plus my turning to food for comfort when the OA became my daily companion put more and more weight on. This of course made matters worse, since more stress was being put on my increasingly deteriorating hips. It's a vicious spiral.
After the surgeries, I lost some weight, but labored to do so, and to tell the truth it was a lower priority to recuperating as well as possible and surviving a divorce. In due time, the hips became better and the divorce came to its uniquely ugly end, but some rays of sunshine came in. I was no longer in this huge pain for many reasons, and life looked better.
I was still overweight, though and finally, when about a year+ on both hips came about, I got motivated. I was not eating overmuch, but the weight refused to come off. This was alarming to me, since I wanted so much to improve in every way. I also wanted to give the hips a fighting chance to go long term.
So I started looking around for something that worked and made sense without being idiotic about it. The fact is that my ex-wife was a weight loss junkie, and tried many plans without any result. The only sure result was that (since she insisted I join each to give her support) with every plan that we tried, I put on 5 pounds. It was almost automatic - sign a check for the fees and 5 pounds of gristle fell directly on me and attached itself. She did go on one after we separated, that worked. For her it included hypnosis and use of a new diet. It is called by many names - paleo diet, prime diet - I prefer 'caveman diet', since it plays to my instincts.
It is basically a diet that is different from the way most western cultures eat, based on not eating any sugars, fake sugars or anything that if consumed by the body would produce sugars. The idea being that introducing sugars into yourself is like building a superhighway to obesity.
Using this process, my ex-wife, my daughter, my sister and her husband (another hippy) each lost a large percentage of weight. I decided to go on it, but didn't want to pay an exhorbitant fee for the hypnosis. A post here pointed me to "Dr. Gundry's Diet Evolution" book,
http://www.drgundry.com/ which I've used to drop 40 lbs (18.3 kg?) so far since February. I am still losing weight on a weekly basis, with my goal being a trim 220 lbs (99.7 kg). I had an assessment done of my non-fat content and it is about 200 lbs (90.72kg), so my doctor and I agreed on that as a target for me with 10% body fat.
I believe it is a healthy way to lose weight and to live from that point on, but it requires a large change in eating style. The focus on sugars means that some of my most favorite foods are gone or deeply reduced in my diet. The book has been easy to use, but does require me to forego anything sugared (easy for me), fake sugared (harder) diet sodas, 'light' ice creams, etc., anything that is a direct source of sugar (much harder) like fruits and fruit juices, and the hardest of all - anything that is an indirect source of sugars from grains. So bread, pasta, rice, beer, potatoes, etc.
I've kept mostly to the diet, with occasional planned slippage. The most frequent miscue has been with beer. You can still drink alcohol, but only red wine and clear alcohols (gin, vodka) in reasonable amounts. I still drink beer, but keep it measured and will frequently substitute wine or spirits. The lack of some vitamins is made up in my case by ingesting multiple vitamins every day, which has helped. I am not starving by any means and am happy with the results.
I've kept my doctor informed about my diet, and she is guardedly happy about the results, she mistrusts fad diets, but this seems to take the weight off an keep it off.
So hope that helps, it does require changes, but I find that I feel better and it works for me.