Try changing chocolates, cakes or crisps for fruit or avoid snacking altogether if you think you may just do it out of habit. The Change4Life website listed in 'Further Reading and References' below gives tips about healthy snack alternatives.
What's more, obese people don't necessarily have slower metabolic rates than thin people, so that whole notion is bunk. The weight loss experts all described to me how they trick themselves and engineer their environments so that maintaining a healthy weight is easier. To get a sense of what you're truly eating, measure your food for a period, suggested Dr. Freedhoff. At restaurants, use your hand to help you estimate portion sizes.