Here, Dr. Robert Mordkin talks to T. Colin Campbell, a professor of nutritional biochemistry at Cornell University who has spent 40 years studying health and nutrition, and is the author of 'The China Study' and 'Whole.'

How has your research impacted what you eat?
I was raised on a farm milking cows, so I started out with the idea that the good old American diet, high in fat and high in protein, was the best there was. When I started seeing some of the evidence in the laboratory, we started eating more salads, dropped red meat, and dropped the dairy probably about 1990. It was a life changer.

How do you see your former diet now?
I look at three different kinds of dietary systems: One is whole food plant based, the second is animal-based foods, and the third is this sort of really odd mixture that we call processed foods. Animal-based foods and the processed foods both have a lot of problems.

But meat itself isn't always harmful.
It's kind of a zero-sum discussion. That is to say, as you add animal-based foods to the diet you're going to basically be subtracting the plant-based foods, so it's not possible just to throw in an extra helping of peas or beans or something like that into the traditional diet because we can't accommodate that many calories basically.

Is there something fundamentally wrong with getting a lot of protein?
The high-protein, high-fat diet that is customarily consumed by the average American promotes inflammatory reaction; there is no question about that. You see a lot of stuff changing in the immune system [with this diet] and other sorts of things that are associated with inflammation that we tend to be familiar with – a risk factor for heart disease as well. A plant-based diet – if you will, that means fruits and grains – that has all the protein we need. As a matter of fact, it's the ideal level of protein.

You essentially advocate a mostly vegan diet. For athletes, too?
A plant-based diet with fruits and grains has all the protein we need. I'm friends with Tony Gonzalez, who was going into his 11th season with the Kansas City Chiefs while following my plant-based diet. He lost weight and called me up, concerned. But he said he felt great – he doesn't have the same pain as the other guys do, he recovers faster, and he's generally healthy. That year he had the most catches, touchdowns, and yards gained in the NFL, breaking. Now he's in his 17th year.

How should someone start transitioning to a plant-based diet?
Smoothies are kind of like a stepping stone for those who want to get a start on this. It's not one of the main ways to do things because one of the problems with smoothies is, although they are quite good, people rely on them too much. What happens is that we gulp down these smoothies, and it escapes the first stage of digestion in the mouth. So [the smoothie] ends up in our stomach, in our intestines, and it creates a glycemic burst and that, in turn, has been associated with a higher risk for diabetes. Still, it's a good way to start.

If we're eating a plant-based diet, should we take supplements, too?
I was the chief witness in Federal Trade Commission hearings when the courts were judging supplement health claims, so I follow the industry closely. It turns out, speaking very broadly, that supplements don't work.