Start with unhealthy high-carb refined grains and add anti-nutrients like lectin and phytates, plus fiber that you would probably be better off getting from whole fruits and vegetables and you don't end up with something healthy.
Pretty much any of the myriad resources on paleo / low-carb / grain-free diets will cover most of the reasons and point to research backing up why whole grains are not healthy. Nutrition science is a weirdly controversial topic however so for every study that points in one direction you'll find someone passionately committed to a different theory who will dig up conflicting evidence.
Having read a lot on the subject over the years (and through personal experience) I'm persuaded by the evidence in favour of a low-carb, largely grain-free, high fat paleo style diet but I've largely given up trying to convince anyone who feels differently on the Internet as for whatever reason nutrition debates are as heated and futile as political ones.
“Lectins and phytates” are the black box doom and gloom ingredients of the paleo world. Let’s straighten up a couple misconceptions:
1. Lectins. Lectins are substances found in many raw foods, like tomatoes, lentils, beans, and whole grains. Some lectins are toxic (like those in kidney beans) and some are completely harmless (like those in tomatoes). Toxic lectins are completely destroyed by proper cooking. Some high lectin foods (like lentils and beans) are strongly correlated with longer lifespans, so diets suggesting they be avoided are probably worth scrutiny.
2. Phytates. Phytates can bind to vitamins and minerals and make them biologically unavailable in digestion. In practice, this is only problematic in already nutrient deficient diets. And like most dietary concerns, the picture is more complex. Phytates also have remarkable positive effects, such as decreased rates of cancer, kidney stones, diabetes, and heart disease.
The paleo diet (basically rebranded Atkins) runs contrary to every developed nation’s dietary guides. To believe it’s healthy is to believe in conspiratorial thinking as silly as flat earth or faked moon landings.
To believe the typical developed nation's dietary guidelines are the best advice on a healthy diet is to show a level of credulity and lack of critical thinking as silly as thinking paleo is rebranded Atkins.
Pretty much any of the myriad resources on paleo / low-carb / grain-free diets will cover most of the reasons and point to research backing up why whole grains are not healthy. Nutrition science is a weirdly controversial topic however so for every study that points in one direction you'll find someone passionately committed to a different theory who will dig up conflicting evidence.
Having read a lot on the subject over the years (and through personal experience) I'm persuaded by the evidence in favour of a low-carb, largely grain-free, high fat paleo style diet but I've largely given up trying to convince anyone who feels differently on the Internet as for whatever reason nutrition debates are as heated and futile as political ones.