The fact is any diet, high fat, low fat, high carb, high this, low that, that totally excludes processed and industrial food has the same results. You lose weight and you get healthier.
More and more studies are linking the micro biome to so many autoimmune diseases, autism (a recent study of kids with autism who received a fecal transplant showed ASD behaviours improved and kept improving even two years after the transplant) , diabetes ... and if you spend a couple of minutes on the "weaning" thread you will see that we start feeding babies crap even before they are 1 year old by giving them melty crisps, waffles and so on.
It is absolutely unsustainable to feed 7.7 billions of humans on meat. The amount of water needed is absurd. To make a pound of beef you need almost 7000 litres of water (to irrigates the grains/grass, drinking and processing) . And you can't minimise the waste's impact. Methane is 23 times more harmful than carbon dioxide for greenhouse effect. 23 more times. And what about cow's poo? Cow's manure goes into waterways when it rains and is the cause of algae bloom . And what about the fossil fuels? It takes 8 times more fossil fuels to produce meat than to produce grains. And never heard of housing shortage? So much land could be used for housing instead of cattle feed.
I think you might want to rely on facts form universities and pubmed for both the health and ecological aspect. This article is a good starting and unbiased starting point on environmental impact news.cornell.edu/stories/1997/08/us-could-feed-800-million-people-grain-livestock-eat
And for the weight loss, eat real food, not too much, mostly plants. Eat 20 different vegetables every week instead of the same ones over and over again . Easily done, it is less that 3/day. So tomatoes, brussel sprout and green beans on Monday, cauliflower, lettuce and red pepper on Tuesday, cucumber, kale and carrot on Wednesday and so on....
I like Michael Pollan a lot more than Pete Evans. Read some of his books or watch some of his speeches, especially those related to his book " in defence of food" which is actually a very good read.
Let me just repeat what I said at the beginning. Any diet that removes processed and industrial food improves health and weight. Eat real food that existed before the industrial food revolution.
And if you really want to know what our ancestors ate, watch this TED talk by an Anthropology professor at Harvard