I would say whether it's water melon or sweet potatoes or donuts or French fries, any food that sends you down that slippery slope isn't going to be helpful when you are trying to become a fat burning beast.
Personally, I ate strict low carb paleo for > a year, no cheats whatsoever, before I knew it, I was a fat burning beast. By that time, fruit, cakes, donuts, chips, fries, pizza...etc had no hold on me.
Today, I can have a piece of chocolate cake and stop there because it's something I almost never do. I won't dream and fantasize about having chocolate cake the next day either.
I think developing the habit of eating right is very important. Doing whatever it takes until the habit is formed is crucial. Otherwise, you'll just keep slipping back to the bottom of the slope and having to start all over again. For me, it took a year of exercising immense will power over my temptation to eat junk.
Now I eat 1 meal a day with no desire to cheat on food quality and feel fantastic while remaining lean in my 40's, and I come from being a fat diabetic.
Last edited by chickenbackside; 07-05-2012 at 08:08 AM.
From my experience it's taking me a lot of disciple to get into fat burning mode. Even if you weren't cheating 3/7, a daily dose of sugar is going to keep you hungry and relying on your next glucose-fix.
If you're quite addicted to sugar (like most people), the transition can take a while. I would cut out the cheat days, and then after a week or so start cutting out the watermelon. You'll want to replace it with something else - replace it with fat! Preferably animal fat. Seriously, I did this (and cut out coffee), and I'm in fat burning mode for the first time since starting this 3 months ago.
Eat what you want to burn.