Gastronomically redundant could also mean to pair foods that are similar to each other. Imagine eating a Cubano Sandwich with garlic bread on the side. These foods (bread/wheat-based) would cause you to get full (satiated) fast and get bloated. Also, they don't do your body any good but add more insulin! But that's beside the point. Haha. In conclusion, don't eat food that doesn't pair well, or gastronomically redundant food.

Gastronomic refers to food, usually fancy food. "Gastronomy" is the art of fine dining (expensive food as opposed to fast food). Redundant means repetitive or excessive or more than is needed. So I guess "gastronomically redundant" means "too much fine food" or something like that? I am having a hard time imagining a context in which this phrase would be used, but maybe that is helpful to you?