I make my own bisto gravy with old fashioned bisto gravy powder and cornflour if I have some meat juices to incorporate into it. 
For example, tonight I am having Liver and onion and when it is cooked i will make old fashioned powder gravy with the juices and some added water.  I'm, not having anything with it, I just fancy a bit of meat tonight. 
  If I havent got anything tasty to add to the plain gravy then I do use bisto gravy granules.  
The amount that we can eat is so small that I dont think a few tablespoons of gravy are going to make a massive difference to the amount of weight we lose.  We are 'supposed' to moist things with our food and I find gravy helps me to digest and I get less food stuck if I have gravy. 
 It is also yummy which is the main reason I have it. 
 Just think, nice lamb chop, couple of sprouts, spoonful of mash and gravy!  Yummy.
Lynne x