Let us start with diet of ancient human beings.Hunters,they were,ate game whether animal or fish and wild fruits and roots.so it is deduced that diet consisted mainly proteins and fats,with little carb from fruits.No body ever heard of modern day diseases including Obesity and Diabetes.Through evolutionary process our body is more suited for low carb and high fat diet.Grains became part of our diet when cultivation started around 10000 yrs. and slowly it became our staple diet ie carb. Became dominant part of our diet.But as protagonist of LCHF say this is (10000 yrs.) too little a time in history for our body to change from what is called paleo diet to high carb diet.That is why these metabolic problems started coming up and now becoming an epidemic.So solution is simple go back to diet of cave man.
The story has in modern times two face one is Ancel Keys and the other is Dr.Bernstein.Evidence suggest that Keys manipulated research findings and lead to wrong conclusion and which in turn gave birth to national policies which completely changed the worlds health scenario .On the other hand Bernstein, a diebetic ,by experimenting on himself came to conclusion diametrically opposite that of ancel keys.Bernstein said LCHF is the key to treatment of Obesity and Diabetes.High fat is not the cause of heart disease or atherosclerosis rather high fat helps in regulation of carb. Metabolism (indirectly).
All the data supporting LCHF is coming from USA and Europe.,where atmosphere is free of pollution ,drinking water is pure and most of the edible are not adulterated and life style is entirely different from ours.Climatic conditions and dietary habits are vastly different.So the researches,results and inferences may not have the same validity here.
We are used to high carb.diet for thousands of years .So to Change the diet abruptly and shift to very low carb may not be very practical as well as may not have many dietary alternatives.That is why start slowly reducing carb add some protein,animal or dairy which will also increase fat.
There are many far more knowledgable persons in this forum who will enlighten us on details of diet.