Yes, the danger I was trying to caution you on was the well known causal relationship of carbohydrates producing blood sugar spikes. That could lead to obesity and diabetes.
The article you site is quite old, published 40 years ago in 1978. While I don't discount medical research based solely on age, there have been a substantial number of studies done over the last 5-10 years which have supported the higher fat diet, as long as those are healthy, natural fats.
I'm glad you brought up the Okinawans and the Adventists. That's a good point I would like to address. The Adventists consume a good variety of foods, and their website includes mentions of "legumes, dairy products, and healthy fats such as olive oil." It also includes fruits, vegetables, and yes, whole grains, while also avoiding processed foods and added sugars. So I wouldn't say they are necessarily low fat. With dairy, olive oil, etc, they are most likely moderate fat. The only real question here is the grains, which I will address next, along with the Okinawans.
It is my understanding that the human body has the ability to store glycogen in the muscles and the liver. The amounts vary per person, obviously, but a good ball park estimate is that the average person can store approximately 350-400 grams in their muscles and another 75 to 100 grams in their liver. At 4 kcal/gram this equates to ~1700-2000 Calories in storage capacity for the average human. Your body uses this as quick-access energy. However, when there is excess from consuming too many carbohydrates or other foods (like dense proteins that also get converted to glucose for storage), the extra remains in the blood, raising blood sugar. Think of it like a tank or a glass and once the tank is full, it overflows and spills everywhere because there is nowhere to store it. That's what you want to avoid - the excess sloshing around in your blood for extended periods of time.
So in the case of people like the Okinawans, I believe they are able to consume a majority of their calories as carbs because they do not consume enough quantity for it to be a problem and are physically active enough to not max out their body's storage tank. This is the same case in my mind for why people in rural China aren't overweight when they consume mostly grains like rice. They are physically active and work outside in things like rice paddies. And much of them are poor and simply cannot afford what is available to you and I in mass quantity for low cost. I could go to the store right now and get 2,000 calories of pure garbage for As far as the grains go, I don't see a real purpose to consume wheat. But there are very nutritious alternatives, such as steel cut oats. I consume those daily, in milk with raisins, flax seed, and crushed walnuts. That's a high carbohydrate breakfast (with high fat as well). My blood sugar spikes usually, but not too high to be problematic. Steel cut oats and hulled barley are extremely nutritious.
My suggestion is still to closely monitor your blood sugar. I still do. Sometimes I find that certain foods or combinations of foods spike me far higher than expected while others surprise me and don't move me that much. The glycogen storage also plays a factor. The more active you are, the more carbs you can probably consume, unless you are carefully monitoring volume of carbs. For example, in the summer if I am doing very laborious yark work in the extreme heat, there is basically nothing I can do afterwards to raise my blood sugar. After 2-3 hours out there working my ass off I can consume copious amounts of gatorade, juices, soda, anything - and my blood sugar won't budge and inch for the entire 2 hour window. Presumably because I have depleted enough of the glycogen storage through physical activity so that whatever isn't needed from the sugary fluids I am consuming goes straight into storage.