Anabolic and catabolic processes
The terms anabolic and catabolic tend to be misused and overgeneralized in popular media
leading to misunderstandings. In a biological sense, ‘anabolic’ means the building of larger
substances from smaller substances. Glucose is synthesized into glycogen, amino acids are built
into larger proteins, and FFA are combined with glycerol and stored as triglycerides (TG).
Anabolic processes occur as a result of overfeeding which raises anabolic hormones, such as
insulin and testosterone, and lowers catabolic hormones such as cortisol and glucagon.
The term ‘catabolic’ refers to the breakdown of larger substances into smaller substances.
Glycogen is broken down into glucose, large proteins are broken down into individual amino acids,
and TG are broken down to FFAs and glycerol. Catabolic processes occur as a result of
underfeeding, which lowers anabolic hormones and raises catabolic hormones. An overview of
anabolic and catabolic processes appear in figure 1.
Figure 1: Overview of anabolic and catabolic processesAnabolic (food intake,hormones,etc) Catabolic
Proteins Amino acids
Glycogen Glucose
TG FFA + Glycerol
Muscle gain Muscle loss
Fat gain Fat lossAn often heard statement is that the ketogenic diet is catabolic. This is true in that all
reduced calorie diets are catabolic. In general, without specific drugs, the body must be in either a
systemically (whole body) anabolic state or a systematically catabolic state. It is quite rare to
see anabolic processes occurring in one part of the body (i.e. muscle gain) while catabolic
processes are occurring in another (i.e. fat loss).
In this respect, the CKD is somewhat unique in that it encompasses a phase which is
catabolic (low carbs, below maintenance calories) and a phase which is anabolic (high carbs,
above maintenance calories).
Anabolism and muscle growth
The catabolic effect of the ketogenic diet has been discussed in detail in chapter 5 and are
not repeated here. Although anabolism is discussed in greater detail in chapter 20, a few general
comments about anabolism and muscle growth are necessary. The exact mechanisms behind
muscle growth are not well understood at this time. In general, it can be said that net muscle
growth requires that protein synthesis be greater than protein breakdown. This assumes that a
stimulus to synthesize new proteins (such as weight training) has been applied to the body.
Therefore, the carb-up could potentially affect muscle growth in two ways. The first would
be by decreasing protein breakdown. The second by increasing protein synthesis. There are
numerous factors affecting both protein synthesis and breakdown. These include the hormones
insulin, testosterone, thyroid, glucagon, growth hormone and cortisol (32). Insulin plays an