I agree heartily with pipermac. Soluble fiber (like psyllium) taken with liquid an hour or two before dinnertime will expand an fill your stomach such that very little food will fill you up.
I defy ANYONE to gain weight on an all-sushi diet. I consider that one of my most conscientious meals and have it as often as my poor pocketbook an bear: sushi isn't among the cheaper dietary choices


!
I'd eat it 7 lunches a week (and 2 dinners) if I could afford it!
Don't believe too much of what you read about the fat-insulin-carbohydrate connection. It's the new FAD and all the diet book purveyors are preaching one or another angle about it...most of it silly nonsense.
Extra calories, whatever the source or whenever eaten, are turned to FAT. Period.