When you examine the studies, the researchers always have evaluated a mixed diet, often the standard American diet, so they’ve looked at the effects of adding fruits and vegetables to the other garbage many people eat. Sure, if the result is that you eat less sugary, oily, processed garbage because you’re eating more fruits and vegetables, then you would expect to see a benefit. Do any studies compare an all-meat or meat-based diet to a more plant-based diet? Nope, no one has ever done that.
