Measurement of a serving

Hi, ormo2000. A tablespoon of any nut butter is considered a serving. With any yogurt, a nutritionist is of course going to say “plain is best,”, but realistically – just note that the flavoring may add carbohydrates, so try to make a natural/unprocessed choice,such as http://chobani.com/products/non-fat-blueberry/ (see the ingredients as an example).

Hi, operagirl. Serving size units for meal planning will be coming out in the near future. In the meantime, the menus from the menu planner can give you an idea, as can the serving sizes for the recipes posted in the Recipes section (link above).
Peanut butter is fine, so long as it is an “all natural” or organic type product. Conventional brands generally have undesirable additives, such as sugar and hydrogenated fats, which can work against your goals.