The key to cheap and non-harmful GNG is to have copious amounts of fats circulating, at a keto-typical low weight that means copious intakes of fats too. GNG ideally shouldn't/wouldn't happen from proteins (unless intake is very high) but from other metabolic byproducts and the glycerol backbones of triglycerides. Then this process typically accompanies ketosis in which ketones (endogenously produced-from-fat-burning types-of-carbohydrate but not from GNG) power most (not all) glucose-but-not-fat-burning-capable cells. Fat-adapted where possible, ketone-adapted elsewhere, and lots of byproducts that ordinarily would be "useless and to be excreted" (not just glycerol but also lactate, pyruvate etc) can now feed into (non-protein) GNG without the complications and expenses and downsides of protein-to-glucose GNG.
