I've been eating pretty close to the McDougall way for half of my 55 years now, and figured it's about time I share what I've learned.
I first read McDougall's books around 1984 or so - I believe there were just 2 books out then. My then-boyfriend was in training for marathons and started noticing that he had a much harder time completing his longer training runs when we'd eaten steak the night before. We started eliminating red meat during his training, and as we both paid more attention to what we ate and how we felt afterwards, we migrated to a plant-based, whole grain, no added oils diet over the next few months. We never made a decision to cut out any food forever, we just cut way back on red meat, then poultry, then dairy and eggs, then fish. We each went through an episode of trying to eat cheese again after going a month or so with no dairy - the way my stomach reacted took away any desire for cheese (including the "fake" soy cheeses) forever. Since we were both young and in good health, we had the luxury of taking the time to try different adjustments to our diet to see how we felt. We both ended up completely losing our taste for any animal products or any oily food.
Jump forward a decade or so, to where I'm in my mid-30's, still eating this way, and still healthy with a BMI of about 21.5. I met my now-husband who was about 40 lbs overweight and trying to get the weight off through sheer willpower. He started eating the same meals that I ate, but switched his nightly pig-out from a pint of Haagan-Daz to a pint of "low-fat" yogurt. I pointed out to him just how much fat was actually in the yogurt, but he stubbornly held on to his comfort food. The yogurt was deceptively labelled - it said "LOW FAT" in big letters, but the fine print showed that it was actually a combination of yogurt (which was low enough in fat to call "low fat") and a lot of other ingredients, most of which added fat or sugar. It ended up being very calorie-dense, with about 50% calories from fat and a whole bunch of sugar.
Even with the yogurt pig-out every night, he started dropped pounds rapidly. Once he hit a plateau, he cut out the yogurt too and the rest of the excess weight dropped off quickly. That was about 20 years ago, and he's now at his high school weight of 160 lbs. Meanwhile, sad to say, his younger brother never abandoned his southern fried diet, and died about 10 years ago of his 3rd heart attack.
So, jump forward again to present day. I'm about to turn 55, my husband is about to turn 68, and we are both in excellent health. He has some arthritis, but not debilitating. He lived a very hard life up until his mid-40's, starting with childhood abuse, followed by alcoholism, cocaine addiction, bar fights, physical labor, etc., so it is truly amazing to see him with no major medical issues beyond worn out joints. I have some disk problems in my neck from a career of hunching over computers all day, otherwise in perfect health.
When so much of the nutrition research started focusing on omega-3's and so-called good fats, I admit to getting a little concerned. I asked my doctor for a full lipid profile - I had only had my total cholesterol tested before. She told me my lipid profile is to be envied - she would love to get all her patients in such good shape. Total cholesterol=154, HDL=75, LDL=70. Apparently I am able to keep in HDL up and the LDL down, in spite of my alleged omega-3 deficiency
She also tested my iron, b-12 status, and anything else she thought might be a problem with my diet. No problems found. The doc says don't change a thing.
I get into discussions online sometimes where I am told that NO ONE can eat more than 100g of carbs (any carbs) without gradually gaining weight and becoming insulin resistant. I tell them I've eaten more than twice that amount every single day for almost 3 decades now, and I weigh in at a whopping 120 lbs. I am usually met with extreme hostility after that. Which is a part of the reason I'm posting here now - it's one place I don't feel like I'm swimming against the current. But more so for others - I know there are a lot of people dealing with obesity, diabetes, high blood pressure, and other serious conditions. I know that eating this way as a lifestyle, not as a diet, will help them. It takes time, and it requires paying attention to what's in your food and to how you feel. It does NOT require an absolute 100% commitment to never eat meat again, or to avoid every drop of olive oil. But as you cut way back on those things, you may find you'd rather eat something that makes you feel good.