What with the world collapsing around our ears, maybe now is a good time to contemplate our post-apocalyptic future. It's become politically fashionable to talk about veganism as the new Heathy Diet; God forbid this should ever happen, because it'll precipitate another apocalypse (involving ecology, economics, and public health). No, the future has fat in it. And fewer carbs.
To explain why, I need to first outline why a vegan planet is a really, really bad idea. Even if you consider a healthier variant which includes saturated fats (from tropical oils), there are three big problems:
1) Despite being omnivores, humans eat a fairly limited range of things. We cannot, for example, digest cellulose or lignin (we can digest some forms of 'fibre' and resistant starch, but our ability to do so depends on our intestinal flora). Many plants are poisonous or unpalatable to us. The vegetables we eat today have been engineered to be a lot tastier than their wild ancestors. Veganism, therefore, means the cultivation of familiar vegetables, and to cultivate vegetables you need all the trappings of modern agriculture: herbicides, pesticides, fertilizers, machines, and fossil fuels. The idea that you can just pick a spot of land and grow tomatoes on it is a silly city-dweller's fantasy. There are any number of things that can happen before you get to eat the tomatoes, and modern agricultural techniques have been honed to address those things. Unfortunately, those techniques are also destroying our planet, and more specifically they're destroying the land on which crops are grown.
2) Vegetables have low energy density and (mostly) a limited shelf life. That means you need to grow a lot of them, and that means (a) more resource-hungry logistics and complex storage and (b) a lot more land being brought into use. Not just any old land, but 'arable' land ... which is in short supply, because we're destroying it all. By, uh, growing vegetables on it. Most farmland loses more topsoil each year than it actually exports in produce.
3) Humans aren't the only animals that like eating vegetables. As mentioned in (1), if you have 100 acres of corn or cabbages, that looks like an all-you-can-eat buffet to any number of wild creatures (mostly small ones). The agricultural-science solution, of course, is to kill 'em all with extreme prejudice. A vegan planet would require wiping out entire clades of critters to keep the supermarkets stocked with vegetables.
We can fix all this with LCHF.
The key point here is that the animals we like to keep for meat, eggs and dairy all thrive well on pasture. "Pasture" just means a managed system of perennial plants, and there are many different climate-specific variants. You can establish useful pasture almost anywhere - even in arid locations, given enough land area and a bit of effort. The plants are usually a combination of native species that arrive by themselves, and a careful selection of introduced ones. When paired with the rooting, scratching, and browsing behaviour of pigs, bovines, goats, and chickens, you get a self-sustaining system that locks in its own fertility, requires almost no management, and exports valuable economic commodities (ie., meat, eggs and dairy).
In many climates you can supercharge this system, either by rotating the animals through the land and following them with annual crops (which thrive on the freshly-deposited fertility the animals leave behind), or by interplanting perennials that humans like to eat, such as coconut, palm oil, moringa spp., or fruit/nut trees. Fruit works especially well with pigs, since they happily eat fallen fruit (I've found turkeys and ducks will too, up to a point).
Chickens can even be rotated through low-growing perennials and/or long-lived annuals like katuk, roselle, okra, chili, allium spp., and grafted eggplant (typically on a solanum capsicoides rootstock). They do nibble on things, but not in a particularly destructive way.
This kind of system ('regenerative agriculture') stops soil erosion dead in its tracks, and in fact rebuilds soil fertility. The output is about half-and-half animal products and vegetables ... which by happy coincidence, is what LCHF adherents would like to eat.
LCHF, Intermittent Fasting and Calories
First day of LCHF lifestyle 
Veganism
LCHF Practitioners - Please be aware!