Fish and Seafood Fish and seafood are an interesting issue on a ketogenic diet. Usually, they are low-or- no-carb. (Some shellfish contain a few carbohydrates in the form of glycogen). On the other hand, as the nutrition gurus of the past few decades have hastened to point out, they are quite low in fat-even salmon, often labeled a “fatty fish”, derives, only 28 percent of its calories from fat.