In all likelihood, most of the anabolic actions of GH are mediated through a class of
hormones called somatomedins, also called insulin-like growth factors (IGFs). The primary IGF
in the human body is insulin like growth factor-1 (IGF-1) which has anabolic effects on most
tissues of the body. GH stimulates the liver to produce IGF-1 but only in the presence of insulin.
High GH levels along with high insulin levels (as would be seen with a protein and
carbohydrate containing meal) will raise IGF-1 levels as well as increasing anabolic reactions in
the body. To the contrary, high GH levels with low levels of insulin, as seen in fasting or
carbohydrate restriction, will not cause an increase in IGF-1 levels. This is one of the reasons
that ketogenic diets are not ideal for situations requiring tissue synthesis, such as muscle growth
or recovery from certain injuries: the lack of insulin may compromise IGF-1 levels as well as
affecting protein synthesis.
There are two thyroid hormones, thyroxine (T4) and triiodothyronine (T3). Both are
released from the thyroid gland in the ratio of about 80% T4 and 20% T3. In the human body, T4
is primarily a storage form of T3 and plays few physiological roles itself. The majority of T3 is not
released from the thyroid gland but rather is converted from T4 in other tissues, primarily the
liver. Although thyroid hormones affect all tissues of the body, we are primarily concerned with
the effects of thyroid on metabolic rate and protein synthesis. The effects of low-carbohydrate
diets on levels of thyroid hormones as well as their actions are discussed in chapter 5.
Cortisol is a catabolic hormone released from the adrenal cortex and is involved in many
reactions in the body, most related to fuel utilization. Cortisol is involved in the breakdown of
protein to glucose as well as being involved in fat breakdown.
Although cortisol is absolutely required for life, an excess of cortisol (caused by stress and
other factors) is detrimental in the long term, causing a continuous drain on body proteins
including muscle, bone, connective tissue and skin. Cortisol tends to play a permissive effect in
its actions, allowing other hormones to work more effectively.
Adrenaline and noradrenaline (also called epinephrine and norepinephrine) are frequently
referred to as ‘fight or flight’ hormones. They are generally released in response to stress such as
exercise, cold, or fasting. Epinephrine is released primarily from the adrenal medulla, traveling in
the bloodstream to exert its effects on most tissues in the body. Norepinephrine is released
primarily from the nerve terminals, exerting its effects only on specific tissues of the body.
The interactions of the catecholamines on the various tissues of the body are quite
complex and beyond the scope of this book. The primary role that the catecholamines have in
terms of the ketogenic diet is to stimulate free fatty acid release from fat cells.
When insulin levels are low, epinephrine and norepinephrine are both involved in fat
mobilization. In humans, only insulin and the catecholamines have any real effect on fat
mobilization with insulin inhibiting fat breakdown and the catecholamines stimulating fat
breakdown.
Liver glycogen
The liver is one of the most metabolically active organs in the entire body. All foods coming
through the digestive tract are processed initially in the liver. To a great degree, the level of liver