Wednesday, December 20, 2006

Thyroid and Fatloss - the condensed edition

Stuff I learned in my recent studies...

The Thyroid gland has many important functions and in the adult its primary concern is to control the Metabolic rate - a subject of great interest to anyone wanting to lose fat or keep it off. I managed to dig up a few papers in my studies that peer closely at what happens to your Thyroid Hormone (TH) levels when you lose fat. It’s veeeery interesting.

A little background Bioscience to start :O) There are two main TH’s, T4 and the more active form, T3. Your Thyroid produces predominantly T4 and most of it is converted to T3 at various sites in your body. T3 is important because there is a direct link between your T3 levels and your Resting Metabolic Rate.

On a reduced calorie diet T3 levels plummet and then they rebound once the diet is over, but here is the catch - they do not return to previous levels, hence the ease at which you can re-fatten yourself. Check out this study. A group of ‘weight-stable-post-obese’ women were matched with their ‘never-obese’ equivalent in terms of Fat Mass (FM) and Fat Free Mass (FFM). The RMR of the slimmed down group was about 8% lower than the other group and this correlated to their T3 levels. I found this interesting because it seems to show that T3 levels are more important to maintaining metabolism than FFM.

The reduction of T3 is more severe in low-carb diets and I found one rat study that showed a good T3 spike with one carb-heavy meal. A single meal doesn’t seem to have the same effect in humans but researchers like Lyle McDonald have discovered that a longer carb-refeed does seem to go some way to getting those T3 levels back up.

So, what does all this mean in practical terms? The first thing that springs to mind is the importance of exercise. If exercise and healthy eating are a habit then it should be easy enough to offset an 8% or so reduction in RMR.. get moving, and keep moving! You can’t turn lazy again once the fat is off! Secondly, I understood a little more about the idea behind incorporated structured carb re-feeds and how to go about them. More about that in a future blog.

Of course I also ended up with a head full of questions. What happens when you diet less vigorously? How much protein were they eating? Can supplementation help? I just know I'm going to be dreaming about this..... ;)


  1. ...I understood a little more about the idea behind incorporated structured carb re-feeds and how to go about them.

    So...I'm guessing that hoeing through an entire Bakers Delight apple & walnut log doesn't actually qualify as a 'structured carb re-feed' then? Damn! THAT'S what I've been doing wrong!

  2. Right! It has to be low fat. Also a longer refeed seems in order. So, taking 'free meals' may work psychologically but doesn't really help the hormones get back to normal. It seems that the minimum would be 5 hours with steady intake of carbs. Then you can get right back to trashing your metabolism :O)

  3. hmm, facinating! Please do tell more when you have the time.


I love to hear from you! Tell me what's in your brain, your heart or your dinner plate :D.