Most people say weight gain is inevitable on prednisone, but it definitely doesn't have to be. Prednisone messes with blood sugars, artificially raising them and causing hunger when we don't need food at all. Hunger is not a reliable signal to eat when on prednisone.

I've stuck strictly to a low carb/high nutrient diet and cut out all processed foods with the chemicals & additives that go with them, and have lost over 2 stone since PMR diagnosis. To summarise my approach:
1. Eat no snacks at all during the day. They raise blood sugar and increase the temptation to eat more.
2. Invent a project that involves movement and distracts from food. For me, it's getting the garden in order, 10-15 minutes at a time, many times a day. My garden is looking great now and the regular outdoor exercise is good too.
3. I eat only between 12noon & 7pm. I do drink full cream milk coffee with meds in the morning and don't restrict morning and afternoon coffees with milk (none after 7pm). Limiting the time you eat helps keep blood sugars lower and helps reduce weight. Use the clock rather than hunger to decide when you need to eat.
4. Drink plenty of water. Prednisone can cause fluid retention so it helps with that. I also drink a glass of water with the first sign of hunger. Sometimes it's water that's needed rather than food.
5. Consider what your body needs. What is in the food? If it's high in sugar/carbs or additives, it's rubbish, forget it. Concentrate on fresh foods, vitamin and calcium rich foods.

It comes down to whether we're willing to change a few habits to benefit our health. I expect it would be harder for people on higher doses of prednisone, but for PMR doses, weight control and even weight loss is definitely achievable.