Living organisms can be thought of as heat machines and metabolism as the inner workings of the machine. The metabolism converts energy from the combustion of food into useful work (mostly chemical work that makes new material for the living cell) so efficiency (useful work rather than wasted heat) can be maintained. Human metabolism has two goals. First, we obviously must maintain energy production, the useful part of which is usually measured by the availability of biological intermediates that can drive life processes. Second, we must maintain more or less constant levels of blood glucose.

In this 2003 article in the CrossFit Journal, Greg Glassman provides a series of observations on the then-current state of the “diet wars” and the growing understanding of the benefits of carbohydrate restriction. Along with a review of “responsible diet books,” he notes: “In the public square, the realization that carbs, not fat, make you sick and fat is spreading rapidly. Spreading like truth unobstructed. The position that carbohydrate is essentially toxic at common consumption levels was a truth suppressed by political and industrial corruption of science and journalism. Suppressing truth is like holding a beach ball under water; it takes constant work against a tireless resistance. They have slipped and our position sits like the beach ball on top of the water, where everyone can see it.”