My concern about low-carb and low-fat is that as the body can only burn carbs in the form of glucose, or fat in the form of ketones as fuel then if an individual is on low-carb AND low-fat, the only other place they could get enough fuel from is their muscles. Of course they feel ok because the body is compensating quietly without their awareness.
As the brain is made of 60% fat and like all cells in the body brain cells die and need to be replaced, where is the body going to get the fat from if not from the diet?
As the lung cells are made from 100% fat where is the body going to get the fat from if not in the diet?
The body can turn glucose into fat, but it can't turn fat into glucose.
Just because we don't drop dead if we don't eat enough of any given food doesn't mean that it isn't causing problems at cellular level without us being aware of it.
Something is causing Alzheimer's. That too, like many other diseases is on the increase - and in relatively young people too. Why? It doesn't happen overnight. Something is triggering it. Could it be the combination of highly-processed foods and low fat? Low-fat won't provide enough of the fatty acids that the brain needs to function with, and the processed and often nutritionally 'dead' food won't supply enough nutrition - in fact much of it actually robs the body of nutrition as the body tries desperately to deal with it. Over a long period of time, those factors have to impact somewhere along the line.....
If nutritional income is less than nutritional expenditure, we will eventually end up in nutrition deficit.
Personally, I would rather look to Ancestral diets - diets that were perfected over thousands of years through the patient trial and error of our forebears. They learned what was good for them and how different types of food should be prepared in order to get the best out of it, and passed that wisdom on to their children. We sadly, have lost that knowledge and understanding. We assume that all food is good food.....