Human beings have been in existence in homo spaiens form for over 2 million years. For 250,000 of those years we evolved into our current homo sapiens form. During this very long era, human beings were hunter-gatherers, hunting animals and their fat for meat and gathering roots and vegetables.
Around 10,000 years ago, grains were discovered and the era of agriculture, the Neolithic era, started. Grains were a source of cheap energy and could last a long time enabling storage and transporation (and hence the spread of civilization) and they could be grown in mass quantities enabling the proliferation of populations.
Think about it…as human being, we have only begun eating grains for about 4% of our existence. We didn’t evolve on that stuff but we did evolve on meat and plants.
Anthropologists can tell at a glance if the remains of a skeletal bones are from the Neolithic (agricultural) or Paleothic (hunter-gatherer) era. The Neolithic remains tend to be shorter, with less bone density and cavity-filled teeth.
Grains are filled with anti-nutrients (like lectin, phytates and gluten) which prevent the absoprtion of nutrients to the body. For more information, click on this great explanation from Mark.
With the advent of mass industrialization of food (specifically the processing of grains and sugar canes into flour and sugar) in the last 150 years plus the subsidies the agricultural industries receive in the past 50 years plus the misguided government nutritional policies that push the idea of processed carbs as the bedrock of a healthy diet in the last 30 years, and you have populations that suffer every sort of ailment unseen in the past…Allergies, dental decay, acne and bad skin, neurological disorders, obesity, cancer, Alzhiemer’s, every kind of chronic illness, etc…
Weston A Price’s “Nutrition And Physical Degeneration” (freely available for reading via project gutenberg) had a central hypothesis that Western diseases from dental decay to cancer, were rarely present in developing societies. His research of isolated and hunter-gatherer tribes across the world (it took him 10 years to complete his very comprehensive study) led him to extrapolate that abandoning traditional diets and adopting the Western diet (flour and sugar based) introduced diseases of the West into societies that never before had experienced them before.