AAAAAH! Another cooking-metaphor film - "soul food is cooking from the heart". Nothing intrinsically wrong with that statement, but in the context of this film, it's about as deep as the water I steam my veggies in.
Big Mama is the matriarch who holds this American family together. A forty year tradition of feasting on -yup!- "soul food" is upheld every Sunday lunch. Here the extended family gets together, to enjoy each other's company, and have their arguments lovingly resolved by Big Mama. This all happens in the world of continually clean and uncreased clothes, where homes are devoid of the wear-and-tear of day-to-day living, and furnishings are artistically placed the same in all the characters' homes. Pretty surreal, and goes to show that Hollywood is getting better at Socialist Realism.
Already unnerved by this unreal world, you know family solidarity is going to crack when Big Mama disappears form the scene and lies in a coma in a hospital bed. Sure enough, bickering and sisterly rivalry ensure that the family don't come together for the traditional soul food.
Things go from bad to worse with arrests, marriagal disputes, infidelity and serious misunderstandings. There is a lesson in here somewhere, especially with Ahmed (the young son / nephew / grandson of the family) stepping in to remind everyone about the value of family, but I don't think its one you or I already didn't know.