Answer :
The most appropriate cause claim for the student researching the impact of food deserts on African American health in communities in south Houston would be:
"A lack of access to fresh produce and a variety of grocery stores have caused increases in obesity and heart disease rates of African American in south Houston communities."
This claim directly links the lack of access to fresh foods and grocery stores with the negative health outcomes experienced by African Americans in south Houston. It highlights the causal relationship between limited food options and the health issues faced by the community. This claim focuses on the impact of food deserts on health outcomes, making it a suitable choice for the student's research topic.