I’ve been <20g of carbs per day since February 2016. My athletic performance was impaired for the first 6-8 weeks, but has since increased dramatically.

At low circulating insulin levels, most cells in your body can efficiently metabolize fatty acids. For the minority of cells that cannot, your liver converts protein into sugar by a process known as gluconeogenesis.

It’s very possible to be a performance athlete and eat very low carb.