Growth Hormone (GH)
Growth hormone is involved in many processes in the body but a primary one in adults is the mobilization of fat. Women show higher levels of GH than men along with an larger increase in response to exercise. This is probably part of why women use more fat for fuel under some conditions.
The hormone insulin is one about which there is a great deal of confusion and mistaken information. While all too frequently blamed for being the cause of fat gain it's better to think of insulin as a general storage hormone. It impacts on fat metabolism, stimulating fat storage and inhibiting fat mobilization and burning but it also increases the storage of carbohydrate in skeletal muscle and liver and is involved in skeletal muscle growth. In general, women have lower levels of insulin along with better insulin sensitivity than men. This is more pronounced during the follicular phase when estrogen increases insulin sensitivity and is decreased in the luteal phase when progesterone causes some degree of insulin resistance.
Almost everyone knows about the thyroid hormone although, like so many things, there is a lot of confusion and misinformation about it. Among its other effects in the body, thyroid hormones are a primary controller of metabolic rate, interacting with other hormones (such as the catecholamines discussed below). Thyroid also impacts on fat cell metabolism (helping to mobilize fat out of the cells) and skeletal muscle.
There are two primary types of thyroid hormone called T4 (thyroxine) and T3 (triiodothyronine) which are released from the thyroid gland in a ratio of about 80% T4 to 20% T3. T4 is primarily a storage hormone which is converted to the more active T3 in other tissues in the body, especially the liver. The conversion of T4 to T3 is important as this process goes down while dieting, leading to lower levels of T3 and a lowered metabolic rate. Reproductive hormones interact with T3, estrogen decreases levels of active thyroid hormone while progesterone increases them. This may be part of the metabolic rate increase during the luteal phase. T3 can also be converted inside of tissues to T2 which has its own metabolic effects there.
Women are significantly more likely to be hypothyroidal (meaning that their thyroid gland releases insufficient levels of thyroid hormones) having more issues when iodine intake is insufficient. They are also three times as likely to suffer from thyroid cancer as men and this is probably related to the direct effect of estrogen on thyroid hormone metabolism. Women are also more likely to suffer from depression and, while far from the only cause, low thyroid levels are an often undiagnosed cause.
All medical cases of hypothyroid are treated with thyroid hormone to replace the hormone that is not being produced normally. Either T4 or a combination of T4 and T3 are typically given and some women report better results from a type of thyroid called Armour. Determination of hypothyroid of any sort must be made through blood tests and medication should be used under the care of a health practitioner. Certain diet and training practices can interact with thyroid and women's levels can be impacted significantly, this effect being both large and rapid. Women's overall dietary choices can also negatively impact on thyroid hormone levels (and by extension their metabolic rate).
The catecholamine hormones refers to adrenaline and noradrenaline in America and epinephrine and norepinephrine everywhere else in the world Adrenaline (epinephrine), as its name suggests is released from the adrenal gland into the bloodstream and has effects throughout the body. In contrast, noradrenaline (norepinephrine) is released from nerve terminals and only has effects very locally where it is released. Many of you may have heard these hormones referred to as the fight or flight hormones although, they appear to have slightly different effects in women.
Released in response to a variety of stressors, the catecholamines raise heart rate, blood pressure, mobilize fuel for energy and have many other functions. In general women show lower levels of the catecholamines at rest along with a generally lower response to exercise compared to men. While women initially increase levels during exercise to the same degree as men, they rapidly adapt to exercise and no longer match men's levels. As with the differences in GH described above, these differences are probably part of why wo