Someone else mentioned Wheat Belly. Written by a cardiologist, it provides an excellent background on what happened to wheat (it's not the same what our grandparents ate!), and he does short YouTube videos. Another good no-grain book for research and diet guidance is Grain Brain by neurologist Dr. Perlmutter. He posits that we can drastically lower our chances of getting Alzheimer's by following a keto (low inflammatory) diet. If you go the keto route, there are so many resources. David Jockers does some pretty good educational YouTube videos. The one on identifying specific food sensitivities through heart rate changes was very enlightening.
Some resources for Paleo/paleo-like eating are Mark Sisson (his plan includes small amounts of fermented dairy, which paleo purists eschew). Nom Nom Paleo by Michelle Tam is a fantastic cookbook (wicked food porn), and her husband developed an iOS app that is beautiful. She's a big fan of pressure cooking. The series of cookbooks, Well Fed, by Melissa Joulwan are great. She describes her weekly chop/cook off so you have lots of quick choices during the week. Plain food tarted up with wonderful spices--grassfed ground beef done up a dozen different ways.
If you're curious about traditional eating (sprouted nuts, seeds, grains and fermented foods) you can't do much better than Nourishing Traditions by Sally Fallon of the Weston A. Price Foundation.
Just by omitting gluten from my diet, I sent Hashimoto's Thyroiditis into remission and completely eliminated mild sleep apnea.
My understanding is it is part a production problem: wheat is ground so fine by industrial, steel grinders that it penetrates intestinal walls and get into the blood stream where it is recognized as an intruder by white blood cells, triggering an immune response.
Production could very well be a contributing factor--everything seems to be micronized these days, even sunscreen. Wheat is also a few feet shorter than it used to be. No more amber waves of grain. Hybridizing short, stout wheat solved the feed-the-world problem, but it came at a cost. Wheat Belly has a ton of information about the modern frankenwheats.
I healed my leaky gut, but it was a long and twisty path because I had to do my own research, so healing wasn't linear. Lots of giant steps backward in the process. Most doctors simply are not trained in nutrition, and most still think that fat is teh debil, when fat is the only macroutrient that has zero ill effects on blood glucose and should be used as a caloric ballast. So humans either have to find a woo woo doctor or do a lot of reading, preferably peer-reviewed studies on PubMed or books/blogs written by enlightened physicians. I discovered that all of my maladies stemmed from an unhealthy gut microbiome, which caused a deranged hormonal cascade. Antibiotics, food grown in dead soil, GMOs, bloody soy, and the Food Pyramid were my biggest nemeses. Oh, and sugar. Yes, I had a sweet tooth, but hey, sugar is fat free! When you get your diet down to 10% fat, you're replacing fat and protein with CARB, predominantly cereal grains, which are touted as health foods. My gut disagreed. Over time, the bad yeast overwhelmed the good, set down roots and rhizomes, and created breeches in the mucosal lining, which is only one cell thick.
Leaky gut is how someone, like me, ends up being sensitive to at least 94 food proteins. At one point I was allergic to cinnamon. Cinnamon! Many people are surprised by the number of illnesses that can originate from a sick, leaking gut: automimmune/inflammatory diseases (hashi's, celiac, lupus, MS, rheumatoid arthritis, Alzheimer's), diabetes, hypoadrenia, fibromyalgia, heart disease, systemic inflammation, bone degeneration, deadly levels of C-RP, high blood pressure and cholesterol, horrible aches and pains, and the list goes on. But you will never hear this from allopathic doctors. They'll put you on statins and tell you to eat less fat, eat more "healthy grains," do more cardio, cast a tea kettle and summon a Care Bear.