Interesting article

Awkward30

I haven't yet looked up the sources to see if I believe that running lowers your metabolism, but that is the premise of this article:

http://articles.elitefts.com/training-articles/women-running-into-trouble/

Anecdotally, I saw similar weight loss between my endurance training period and my strength training period, but since I have gained a slight amount of muscle since I started strength training and almost 1/4 of what I lost when I was running was muscle, I lose much more fat while strength training...

Anyways, I thought this was interesting!

Awkward30

bump because it is actually interesting!

BrianSharpe

Gave it a quick read, sounds a little like broscience to me but I'll have a look at some of the studies he refers to, it's easy to misinterpret correlation for causation which may be the case here (I've yet to read anything that suggests steady state cardio causes hypothyroidism)

Toddrific

Referenced study one basically discovered lower thyroid and leptin levels in some exercising women. They noted no change in mass or body composition.

Study 2 notes hormone changes but notes an increase in lean body mass.

Study 3...huh? Appears rowing lowers thyroid hormones, but stops at some set point.

Edit really 80 studies...?

Study 4...having a negative energy balance messes with hormones in twins.

5. Suggests thyroid hormones play a role in physical conditioning.<<<

6. Increasing exercise without increasing caloric intake results in lower thyroid hormones.

Meh, enough for me. Basically thyroid hormones change in response to exercise. I none of the studies so far state this is a bad thing.

Awkward30

I didn't think it seemed bro sciencey, since I rarely find fitness/exercise articles that cite primary literature in the first place. I've looked up a few of the references, but my complete ignorance of physiology is getting in my way. Took me months in an immunology lab before I figured out that a thymus is not actually the same thing as a thyroid. Who thought that naming was a good idea?!?

So, things that I did find interesting from the cited literature:

Some of it was done in rats... why on earth would they do something as unintrusive as cardio and testing blood levels in rats? lol

Clin Endocrinol (Oxf). 1984 Jun;20(6):657-69.
The thyroid function in young men during prolonged exercise and the effect of energy and sleep deprivation.
Opstad PK, Falch D, Oktedalen O, Fonnum F, Wergeland R.

Thyroid function has been investigated in 24 young military cadets participating in a 5 d ranger training course with heavy physical exercise, calorie deficiency and deprivation of sleep. The cadets were divided into three groups, each differing in the amount of sleep and food consumption. The serum levels of thyroid hormones (T4, FT4, T3, rT3) and TBG showed a biphasic pattern during the course. Initially there was an increased secretion concomitant with an increased deiodination of T4 to T3 and rT3 mainly due to physical exercise. When the activities lasted for several days without sufficient food supply the thyroid secretion decreased simultaneously with an alteration of the peripheral conversion of T4 to rT3 instead of T3. A significant correlation was found between the changes in total and free thyroxine (r = 0.9) and between the increase in rT3 and decrease in T3 (r = 0.6). TSH decreased during the first day of activities and remained low throughout the course. The TSH response to TRH stimulation was greatly reduced during the course due to physical exercise and calorie deficiency. The present investigation demonstrates that the thyroid function is strongly affected by prolonged physical exercise and a negative energy balance, whereas sleep deprivation does not have any significant influence. The results indicate that the alteration observed is not regulated just by the hypothalamo-pituitary-thyroid-axis alone.

A similar study looked at female endurance athletes and found only minor changes, but its not open access and my school doesn't subscribe



Overall, I buy the premise that thyroid function is important to metabolism, I buy that endurance training isn't doing any favors there, so it logically follows that endurance training just for the sake of weight loss isn't a good idea.

Toddrific

I think I can sum up the article by saying it's author bias so they can sell more fitness equipment.

Running, you don't need to buy any of their stuff.

The modification of thyroid levels appears to be an adaptive response to physical exertion.