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I wondered if any of the cavemen here have tried a ground beef-only (or close to only) diet? If so, I wondered about your success/failure, lessons learned, etc.
I haven't ever, but I would guess that you're better off getting a mix of protein sources. But if you do go only ground beef for a protein, I would recommend finding a way to still get some greens into your diet. Spinach, kale, chard, mustard greens, whatever... you need fiber too.
Another concern is that it's tempting to go for ground beef for economic reasons as it's one of the cheaper meats. But according to news reports up to 70% of store bought ground beef contains "pink slime", ammonia-treated protein filler. And there's no way that stuff is paleo-friendly.