Fava Beans (also known as Broad Beans) and all legumes, are a grey area in low-carb eating. One the pluss side, they're high in fibre and have reasonable amounts of protein. They are also low-glycemic and compared to grains, are less likely to spike insulin in small qtys. However, due to their high carb content, and their high volume in some diets, they have a high glycemic load. Potatoes and rice are the same in many other diets. They will never be as good as fibrous vegetables. You're really not eating low-carb as long as you are eating beans, potatoes, rice or grains. These can be added back in moderation once you've reached your goals and you know what you can tolerate.
As an example, 1 cup of lentils has 40g of carbs along with 18g protein and a little fat. Almost half those carbs are fibre and 1 cup is very filling. In a normal diet. That volume of carbs would not be problematic. With a small piece of meat and a small salad, this would be a greal meal and would keep insulin in line quite nicely. You just have to careful with the qty.
http://www.whfoods.com/genpage.php?tnam ... le&dbid=43
Also, all dried beeans need to be soaked and cooked but that's probably obvious to you.