even better than sugar and bread are meat and dairy products.
just because you don't gain weight off big macs doesn't mean you aren't gaining cholesterol, clogged arteries, chemicals unknown, and so much salt your heart may explode from high blood pressure.
to lose weight I have found nothing like a Vegan diet. I used to weigh 200+ with a damn near 40" waist. I now weigh about 140-145 with a 28" waist. The doctor gave me a blood test because my dad has high cholesterol and blood pressure and he was amazed with the results for my age (37). Excellent good cholesterol and very low on the bad.
besides.. who wants to eat dairy? Did you know that it all carries puss and infection? There is an acceptable level of puss in dairy for every state.. look it up if you want to be disgusted and now how many infected white blood cells you intake.
Veganism is great. I did it for a while to lower my cholesterol and lost weight and felt good. It's just not a diet i can stay with successfully for very long. And my cholesterol is currently fine. But veganism has a lot going for it.