I gain weight in the fall and winter due to BAD thyroid problems, and lack of exercise. I am 6'1 and 280 pounds. I always thin out during spring and summer. To about 220. Instead of just going to uni and then sitting around studying, I am trying to make myself more active during the colder months. I usually walk 3.5 miles a day(I have bad knees, and my lower back hurts even when walking, but worse when running)

Anyway, so with staying active and keeping with my replacing one meal with a salad(as I do during the spring/summer months) I am trying to stay away from heavy foods(like chips, meat etc, potatoes, etc..) which I LOVE during the fall/winter, instead of cutting them out completely I have been thinking of having a smoothie as a replacement meal.

My smoothies are:
One yoplait single serving cup, either strawberry, harvest peach, plain, or blueberry
Some frozen strawberries(about 6)
Some frozen pineapple chunks(again 6)
and some raspberries(usually 6)
I like my smoothies runny, so I add at least a cup of orange juice. They are so good, and usually make two smoothies. So I freeze the other one and save for a snack later during the day.

Does this seem like a good idea? Salad, Smoothie, regular meal, smoothie ? Plus 3.5 miles walking. Takes about 1.3 hours to walk in total. I also walk to my classes, etc.

Thanks!