How has the quality of the food we eat changed since the agricultural revolution?

They are completely right

According to a recent study at the University of Colorado, the nutrient density of food has declined significantly over the past 100 years. In fact nutrient density has declined approximately 40-60% over the past 100 years. That means that our food today typically has 50% fewer nutrients compared to the food that our grandparents ate.

Nutrients such as the vitally important vitamins, minerals, anti-oxidants and phytochemicals are the foundation of healthy cells and a strong body. Today, if you ate the same amount of vegetables that your grandparents ate you would only receive half the nutrients.

Also your grandparent consumed on average 131 pounds of homegrown vegetables every year compared to 11 pounds today. And a recent study showed that only 11% of Americans eat 2 fruits and 3 vegetables every day. This unhealthy combination of nutrient poor foods and reduced intake is an open door for disease, especially if it is applied over a lifetime.