Don't use your imagination to worry, use it to create possibilities
I think if you are looking to became a healthier, more active person, the most important thing to do is not to feel sorry for yourself for what you can't eat or do anymore. Because it isn't a case of "not being allowed". It's a case of choosing the better option, and see what benefits and good it does for you.
I think many would need to stop and think to themselves "How do I feel? How does my head feel? My muscles? How am I sleeping? How's my mood?"
I think a lot, and I mean a lot, of our wellness comes from what food we eat and how we exercise. Sugar, for example, causes our brains to behave in the same way as cocaine. It is also now related to diseases such as alzheimers and dementia, because it affects the nerval endings in our brain. Scary, huh?
So what are you actually missing out on? I think we need to become more aware of the direct chemical effects food have on our bodies. We must not forget that our bodies will digest, and process all the food that we eat in order to fuel our cells. It does make a difference if you choose to eat a bag of sweets as a snack or a couple of fruits.
Of course you can still eat sweets, cake and all those nice foods, but that should also be a choice. Not because you have an addiction to it and just grab it in the shop every time you go shopping. You can say yes to treats, but you should also be able to say no.
Back to the positive thinking then. Imagine loving yourself. Looking at yourself and accepting yourself. Look at what you do for yourself and your body. If you think something should change, make the change, see the possibilites. You are strong enough, because you can only gain from doing a positive change. You can start by saying "I love my body for what it is, and I will treat it the way it deserves". Feed your body all those delicious, lovely and healthy foods, that will not only make you feel happier chemically but it will also make you happier psychologically. Exercise because not only will it make your body stronger, but it will boost your confidence and self-love. That is proven.
So what are you waiting for? :)