Maybe it's not "optimal" but considering that obesity, heart disease, diabetes, cancer, etc rates have all been climbing like crazy for the last 50 years and the diet has changed a lot in the last 50 years, it's not outside the realm of possibility that the change in diet is causative towards these outcomes rather than simply correlated.
And considering how long it's going to take to sort it out definitively, you might have to go most of your life making decisions based on a hunch rather than with proven science. It sucks, but that's life.