Carol,
I know that prednisone changes our metabolism and redistributes fat to our abdomen, face, and back. Been taking pred since 2005 and hope to be off later this year. I lost 40+ lbs of muscle due to polymyositis and have gained the weight back (not all of the muscle) and now weigh the same as I did before getting sick and the same as I did at 16...almost 50 years ago. It is possible to control your weight while on pred (I started on 60mg and am down to 8mg) but it is more difficult. I needed to gain some weight back and allowed myself to do it. Once I hit my goals I started a plan to control what and how much I ate. Went a little over my ideal weight but have lost that in the past 2 months.
Do not believe in diets but in eating healthy and changing your eating habits if necessary. We all have comfort foods that are probably very high in calories and have little or no nutritional value. IN times of stress we tend to eat more of those foods. If you combine increased inactivity due to disease and lower metabolism due to meds and/or less muscle mass, that is a formula for gaining weight. It is not just the prednisone although many blame it on the meds.
Look at what you eat and when. Eliminate the high calorie foods and substitute them with more nutritional ones. Reward yourself weekly with small servings of your favorite "bad" food so that you don't go crazy and abandon all attempts to control your eating habits. Eat smaller portions. Increase your activity, even if it is just walking for a few minutes daily. All of this has a cumulative effect and over time will result in weight loss. A small reduction of 250 calories daily and an increase in acivity to burn 250 calories will result in a 1 lb per week weight loss. I have seen studies that losing more than about 5 lbs per month makes it difficult to retain the loss.
Our bodies are conditioned to respond to lower calorie intake by lower your metabolism as well. Diets will work temporarily but without a change of eating habits your body will not adjust to a different weight level.
I am not a nutritionist but have been able to maintain a healthy weight my entire life by being prudent. Only gained significant weight once after an injury but was able to lose it all through exercise and portion control. Ate pretty much what I wanted but in lower amounts.
Bill