Ppelroth,
I followed the Weight Watchers plan while riding anything from 30 to 150 miles a week. I managed to get rid of 3 stone. Although it did take the best part of a year. But what I found was that I'd have to stick to their points system Monday to Friday (this is when I'd do the 30-35 miles to and from work) Then on the weekends when I would sometimes ride 70 one day and 80/90 the next I'd just eat what ever I wanted. This took a long time to figure out as I was trying to keep within the points and still ride 70/80 miles, I'd generally hit the bonk before lunch time then again in the afternoon. Now that I've hit my target weight I find on long day rides I go with everyone else and have a scone at both morning and afternoon coffee break and make sure I take something really sensible for my lunch - like pasta or rice with veg.
Just don't be tempted by any of the diet plkans that make you miss out a whole food group like Aitkins- no carbs is no good.
But like MM said, first you need to asses if you really do need to shed weight or if you'd just like to be a bit more trim.
Hope this helps.
Jacqui.