the reason it has 'less fat' is because those bison are grassfed.
10-15 years ago it was impossible to find grassfed cows in the USA unless you lived in a large city with people who wanted that.
nowadays every whole foods has grassfed beef so unless you live in a town where they bang their cousins you can access it so no need to buy bison meat. i buy the grassfed beef for my burgers once a week, can't beat it. also keep in mind just cause it says grassfed, that only means at some point the cow ate grass. so make sure you find a legit product, the ones they sell at WF the cows have spent their life eating grass.
but to answer your first question you don't buy grassfed beef cause it has 'less fat'. fat that came from nature is not bad for you lol. (if you don't think so then go read a fucking nutrition book). you get grassfed because the meat is packed with nutrition, while cheap walmart meat is devoid of everything cause the animals are fed shit their whole lives.
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