Sorry, but both kinds of studies are useless. Your proposition is observational and needs a big sample. (Not that any nutritional study does not need one, just

Sorry, but both kinds of studies are useless. Your proposition is observational and needs a big sample. (Not that any nutritional study does not need one, just an order of magnitude bigger.) Tomato juice is liable to get lost in the noise of various diets and genetics unless you truly control the whole of the diet, which is reasonably easy to do with free, well done boxed meals. Then you just need a sample size of few thousands instead of few hundred thousand.