Not sure about any studies but I definitely find what I eat affects my waistline in the immediate future  I also think that by eating healthy we set a good example for our littlies.

I'm pretty good mostly, my only downfall when BFing (and beyond) was chocolate and wine but I don't have too much of either. 

When Bfing I did find I'd get cravings for certain foods I wouldn't normally eat eg.  I don't eat nuts but for weeks I couldn't get enough of peanut butter on toast.

You said you're grazing during the day, are you doing this because you're hungry or just because the foods there?  I find filling up on wholegrain low GI carbs at meal times keeps me from snacking during the day, good carbs is particularly important when you're feeding a growing toddler.  Try porridge at breakfast time with raisins or unsweetened jam for a bit of flavour and you'll find you won't want to eat anything for another few hours.  Have some wholegrain toast or bread with your lunch for the same reasons.  The other trick I tried once upon a time when dieting was I only allowed myself a sweet treat after I ate a vegetable or piece of fruit.

If you actually set aside specific meal times (including a morning and afternoon tea) throughout the day and plan ahead to eat healthy at those times you'll find it easier to eat good meals, snack less on junk, take a few minutes for yourself and set a good example for Lucas.

Finally I'd say remove temptation.  If you always find yourself drawn to the chocolate in your bedroom stop buying it.