People will often say to strictly monitor protein on a fat loss or ketogenic diet because excess protein will be converted to sugar. Outside of medical contraindications of higher protein consumption, I would argue that protein should be monitored when conservation or gain of lean mass is important to the dieter in order to assure enough is being consumed rather than to limit gluconeogenesis. The reason for the latter is that there are well established levels of protein beneficial for body composition while the scientific literature has thoroughly supported that gluconeogenesis is a demand driven and not supply driven process and that excess protein does not result in a subsequent increase in gluconeogenesis (Fromentin, Et al.). It may, however, trigger glycogenolysis which is where some of the confusion on protein consumption may arise.
Glycogenolysis is the process where stored glycogen (either from the liver or muscle tissue) is converted to glucose-1-phosphate and then to glucose-6-phosphate. Glucose-6-phosphate is then either used for glycolysis to breakdown more glycogen or directly converted to glucose for immediate use or storage elsewhere.
Gluconeogenesis is the generation of glucose from non-carbohydrate carbon substrates. Although this can be done with lactate and glycerol, most people are familiar with amino acids (protein building blocks) being the main substrate for gluconeogenesis.
So, glycogenolysis draws on current carbohydrate stores while gluconeogenesis makes new carbohydrate to be used in the body. Both processes are important in the body for providing glucose when needed. However, it is important to distinguish between the two when talking about diet because they hold different implications for how the body reacts to ingested protein.
This distincting is especially important for those following low carb diets for fat loss. Many individuals will limit protein in fear that it will either limit the level of ketosis they are in or increase insulin levels and lead to fat gain. While the former may be likely in a window shortly after protein ingestion the expected uptake of glucose to restore the glycogen that was depleted should limit the the long term effect of acute change fat accumulation and metabolic differences. By avoiding protein you may be limiting your capability to gain or keep lean mass. If body composition is your primary goal it is better to eat sufficient protein, which most agree on 1.8 g/kg ffm or 0.82 g/lb ffm to be sufficient, but a meta-analysis by Morton, et al showed most benefits peak at ~1.6 g/kg ffm or ~0.73 g/lb ffm, and use your other macronutrients (fat and carbohydrates) to fill varying energy needs.
Fromentin, C., Tome, D., Nau, F., Flet, L., Luengo, C., Azzout-Marniche, D., . . . Gaudichon, C. (2012). Dietary Proteins Contribute Little to Glucose Production, Even Under Optimal Gluconeogenic Conditions in Healthy Humans. Diabetes, 62(5), 1435-1442. doi:10.2337/db12-1208
Morton, R. W., Murphy, K. T., Mckellar, S. R., Schoenfeld, B. J., Henselmans, M., Helms, E., . . . Phillips, S. M. (2017). A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British Journal of Sports Medicine. doi:10.1136/bjsports-2017-097608