The second thesis statement, "Because junk food is bad for your health, the size of sodas offered at fast-food restaurants should be regulated by the federal government," can be argued and proven with evidence in an argumentative essay. This statement presents a clear position that can be supported with reasoning and evidence regarding public health, government regulation, and the impact of junk food on society.
The first statement, "Junk food is bad for your health," is more of a claim rather than a thesis, as it does not present a clear argument or a specific position that could be defended or refuted in an essay. It could be used as a point of discussion within a broader argument, but it does not offer a debatable assertion or a call to action like the second statement does.