Academics aren't any more free from the influences of corporate money than anyone else. They are totally dependent on funding in order to get published - and if you don't get published, your academic career kinda goes down the tubes. So who funds nutritional studies? Companies who want to put nutritional claims on their products, and the health-related branches of government, who are themselves heavily lobbied by Big Ag types.
Let's say you're a nutrition researcher working at a reasonable-sized university. You've heard of this "Primal/Paleo" diet thing and you'd love to do a long-term study on, say, its capability to reverse non-alcoholic fatty liver disease. You'd need some funding, a good swack of doctors willing to get their patients to participate, and a couple of months, minimum, to invest in this. Where would the funding come from? There are no drugs involved, no manufactured foods, and it's too simple to require and significant medical oversight. So, unless you have an interested philanthropist onside, or you're sleeping with the dean/department head, you don't get funding for this. But, if a drug company came up with a pill that combined an omega3-6 balancing agent, vitamins D, K2, several B-complexes or whatever, a bunch of minerals and antioxidants, and you wanted to see if THAT would clear up a fatty liver, you would have funding thrown at you and you'd be enjoying expensive single-malts while your test subjects "inexplicably" ended up hospitalized.