Red blood cells are the most limited of the extrahepatic tissues because they do not contain a nucleus or other cell organelles, most notably mitochondria.
Figure 7.341 Red blood cells do not contain mitochondria1
As a result, compared to the extrahepatic tissues, in red blood cells the following pathways are not performed or are not important:
Glycogen synthesis and breakdown
Fatty acid synthesis and breakdown
Triglyceride synthesis and breakdown
Protein synthesis and breakdown
Ketone body breakdown
These pathways are crossed off in the figure below.
Figure 7.342 The metabolic pathways that are not performed or important in the red blood cells, compared to extrahepatic tissues as a whole are crossed off2
If all those pathways are removed, only glycolysis is left, where pyruvate is converted to lactate.
Figure 7.343 Red blood cell metabolic capability
Thus, red blood cells are one-trick ponies, only being able to perform glycolysis and produce lactate.
Figure 7.344 Red blood cells are one-trick ponies