Chapter 1:
Introduction to the ketogenic diet
Many readers may not be familiar with the ketogenic diet. This chapter discusses some
general ideas about ketogenic diets, as well as defining terms that may be helpful.
In the most general terms, a ketogenic diet is any diet that causes ketone bodies to be
produced by the liver, shifting the body’s metabolism away from glucose and towards fat
utilization. More specifically, a ketogenic diet is one that restricts carbohydrates below a certain
level (generally 100 grams per day), inducing a series of adaptations to take place. Protein and
fat intake are variable, depending on the goal of the dieter. However, the ultimate determinant of
whether a diet is ketogenic or not is the presence (or absence) of carbohydrates.
Fuel metabolism and the ketogenic diet
Under ‘normal’ dietary conditions, the body runs on a mix of carbohydrates, protein and fat.
When carbohydrates are removed from the diet, the body’s small stores are quickly depleted.
Consequently, the body is forced to find an alternative fuel to provide energy. One of these fuels is
free fatty acids (FFA), which can be used by most tissues in the body. However, not all organs
can use FFA. For example, the brain and nervous system are unable to use FFA for fuel ;
however, they can use ketone bodies.
Ketone bodies are a by-product of the incomplete breakdown of FFA in the liver. They
serve as a non-carbohydrate, fat-derived fuel for tissues such as the brain. When ketone bodies
are produced at accelerated rates, they accumulate in the bloodstream, causing a metabolic
state called ketosis to develop. Simultaneously, there is a decrease in glucose utilization and
production. Along with this, there is a decrease in the breakdown of protein to be used for energy,
referred to as ‘protein sparing’. Many individuals are drawn to ketogenic diets in an attempt to
lose bodyfat while sparing the loss of lean body mass.
Hormones and the ketogenic diet
Ketogenic diets cause the adaptations described above primarily by affecting the levels of
two hormones: insulin and glucagon. Insulin is a storage hormone, responsible for moving
nutrients out of the bloodstream and into target tissues. For example, insulin causes glucose to
be stored in muscle as glycogen, and FFA to be stored in adipose tissue as triglycerides. Glucagon
is a fuel-mobilizing hormone, stimulating the body to break down stored glycogen, especially in the
liver, to provide glucose for the body.
When carbohydrates are removed from the diet, insulin levels decrease and glucagon levels
increase. This causes an increase in FFA release from fat cells, and increased FFA burning in the
liver. The accelerated FFA burning in the liver is what ultimately leads to the production of
ketone bodies and the metabolic state of ketosis. In addition to insulin and glucagon, a number of