Aug 2011 20
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Triiodothyronine, also known as T3, is the big daddy of thyroid hormones. It affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate. And study after study has shown it is lowered by low-carb diets.

Jay writes:


I thought I'd give you a heads-up on an article at that discusses your “Is a Low Carb Diet Bad For Your Thyroid?” article. The author, Mario Renato Iwakura, dismisses your assertion that carbohydrate restriction lowers T3 levels and instead blames the polyunsaturated fatty acid content of the experimental diets:

By the way, when I last emailed you, I was 195 in 4 months. Now I'm 180 in 5 and 1/2 months! You're right ... total calories are king.  I upped my carbs to 50% and still losing 2 pounds a week.



Anthony replies:

Hi Jay,

I just read through Mario Iwakura’s article and the comments section, and once again am left shaking my head at the blatant reality evasion that has become the hallmark of low-carb advocates. It’s yet another classic example of how low-carbers single-mindedly plod through life, refusing to even acknowledge the existence of contradictory evidence to their beloved yet fallacious beliefs.

In a nutshell, Mario’s article is a complete joke. That Paul Jaminet describes him as’s “resident thyroid expert” suddenly casts the quality of that site’s information in a whole new light.

When you point out to Mario that I already addressed the polyunsaturated fatty acid (PUFA) issue, he replies:

“Yes, I saw his replay [SIC] to your e-mail, but nothing he said convinced me.”

So that’s it. With a single throwaway line, Mario conveniently discards my PUFA discussion and refuses to even acknowledge any of the points I raised. And of course, the moronic low-carb haters in the comments section are just fine with his evasiveness. Case in point is “Franco” who, under the safety of anonymity and distance, so bravely writes:

“Bashing Colpo and PUFA in one single post! It can’t get better then [SIC] that! ”

That single sentence pretty much sums up the deranged low-carb attitude towards scientific debate. For these vicious little misfits, it’s not about an impartial search for the facts, it’s all about grasping any opportunity to smear your opponent and getting the smug, warm, fuzzy feeling of having your beliefs validated. Well, Mario and the heroic Franco may not want to address the evidence that contradicts their pro-low-carb hypothesis, but I certainly will. Before I do that though, I want to address another comment by Mario. He writes:

“In the Stephan post there is also an example of a human study that man gained more body fat on a diet high in linoleic acid, just like the rat study.”

Unbelievable. I gave a detailed dissertation on why this study could not even begin to be used as evidence for the weight-promoting effects of PUFAs, but of course, Mario isn’t having any of it. It doesn’t confirm his confirmation bias, so he simply dismisses it without so much as a cursory discussion: “Nothing there to convince me, so case closed. Next!”

Hear no evil, see no evil: The official low-carb policy for dealing with contradictory evidence.

Sorry Mario, but real science doesn’t work like that. You can’t just dismiss a compelling argument based purely on your own personal whims and fancies.

Even Stephan Guyenet no longer considers the “human study” (Dayton et al) to be convincing evidence of anything, as his most recent blog post attests:

For those of you who want to learn for yourself why neither Stephan nor myself consider the Dayton study to constitute anything resembling proof about the role of PUFAs in weight gain, you can read my original discussion of it here. The full text of the Dayton study can also be found at the above link so that you can peruse first-hand the data and study methods for yourself.

Iwakura et al are trying to shift the blame for low-carb-induced reductions in T3 on to the polyunsaturated fatty acids found in vegetable oils. Don't believe them. Yours truly avoided these fat sources like the plague and still suffered euthyroid sick syndrome on a low-carb diet.

How Low-Carb Diets Lower T3 – It Ain’t the PUFAs

The likely mechanism by which low-carb diets lower T3 levels is hardly unknown and has in fact been elucidated by numerous researchers (and also in my Is a Low Carb Diet Bad For Your Thyroid? article). Here’s Bisschop et al on the subject:

“Apparently, isocaloric carbohydrate deprivation induces a catabolic state with respect to protein metabolism compared with diets with a normal composition and compared with starvation. This catabolic reaction to carbohydrate deprivation is associated with decreased insulin secretion. Apparently, exogenous carbohydrates and/or insulin induced by exogenous carbohydrates are required for a proper utilization of dietary proteins.”[Bisschop 2001]

I’ll discuss this some more in a second, but first there’s one other comment I’d like to make in regards to the Dayton et al study, and this applies not so much to Mario but the low-carb crowd in general. The Dayton study was not designed to examine the role of PUFAs in weight gain/loss; the real purpose of the study was to determine changes in blood and tissue lipid levels. There have however, been studies that did examine the role of PUFAs in weight loss/gain. One of these was conducted by Kasper et al. Now, I’ve made no secret about just what I think of this so-called ‘research’ - I’ve discussed it in detail here. But to quickly recap, this crew compared MUFA and PUFA-rich diets, and reported weight loss on the PUFA diet but not on the MUFA diet. What’s more, the astronomically high caloric intakes allegedly consumed while this weight loss was supposedly occurring would indicate that PUFAs accelerate metabolism to a greater degree than a hyperactive thyroid on jet fuel. Again, as I discussed here, all evidence reports to these results being complete crap, but that doesn’t stop the low-carb movement from citing the aforementioned study as ‘proof’ of a metabolic advantage.

So, my flabacious low-carb friends, which is it? You really need to make your minds up on this, because you can’t have it both ways. PUFAs either cause weight loss, or they don’t. You can’t embrace the results of a study claiming that PUFAs turn your thyroid into a raging furnace that melts fat away even under conditions of gross overfeeding, but then turn around and claim that PUFAs suppress thyroid hormone levels and cause weight gain in an attempt to rebut me when I point out the well documented links between low-carb diets and low T3 levels.

That my friends, is known as hypocrisy, and you low-carb jokers exhibit it in spades.

Here Comes the Boom!

Awrighty … time to get down to business and blow the "It's not low-carb, it's the PUFAs!" hypothesis into oblivion. To get the ball rolling, ladies and gentlemen of the jury, I would like to call to the stand the following study:

Danforth E Jr, et al. Dietary-induced Alterations in Thyroid Hormone Metabolism during Overnutrition. Journal of Clinical Investigation, 1979; 64 (5): 1336–1347.

My dear jurors, Mr Iwakura is claiming that it is not carbohydrate restriction but omega-6 polyunsaturated fatty acids responsible for the reductions in T3 observed time and time again on low-carb diets. However, as you scan through the above paper, you will notice that one of the groups followed a zero-carb diet consisting of nothing but lean meat, fish, fowl, and vitamin and mineral supplements. In other words, they ate next to no PUFA. During this very low PUFA diet, T3 concentrations fell steadily and at six weeks were equivalent to those found after 7 days of fasting (88 ng/dl)!

Ladies and gentlemen, that pretty much destroys Mario’s hypothesis right there, but I’m not done yet folks, nosirreee. Your honour, I would like to bring back to the stand the following paper:

Bisschop PH, et al. Isocaloric carbohydrate deprivation induces protein catabolism despite a low T3-syndrome in healthy men. Clinical Endocrinology, 2001; 54: 75-80.

As you look through this paper, my dear jurors, you will see that Dr Bisschop and his colleagues from the Netherlands measured thyroid hormone levels, resting energy expenditure and urinary nitrogen excretion in six healthy males after eleven days of 3 isocaloric diets containing 15% of calories as protein and 85%, 44% and 2% as carbohydrates. The diets supplied 33.1 calories per kilogram of bodyweight, which is the equivalent of 2,483 calories per day for a 75 kilogram person.

The results were pretty much what anyone who is not a hopelessly biased low-carb shill would expect. In contrast to the high- and intermediate-carbohydrate diets, carbohydrate deprivation decreased plasma T3 values (1.78 and 1.71 vs. 1.33 nmol/l, respectively, p 0.01), whereas reverse T3, T3 uptake and free T4 levels increased simultaneously compared to the two higher-carb diets. TSH values were not different among the three diets.

As with the Danforth study, dear jurors, Mr Iwakura cannot even begin to blame PUFAs for the decrease in T3 on the low-carb diet. I emailed Dr Bisschop for the fatty acid composition of the diets employed in his study, and he so kindly sent me the requested data by return email. Unlike many of the previous studies where the fat intake of the low-carb diets was boosted by n-6-rich oils like corn, Dr Bisschop and his team used liquid formulas with a far more balanced fatty acid composition. The data show that n-6 PUFA (linoleic acid) constituted only 20% of the fatty acid content of the mixed and low-carb diets (the fatty acid content of the highest carb diet was next to non-existent). A further 1.5% was derived from n-3 PUFA (alpha linolenic acid). The remaining 78.5% - over three quarters – of fats on both diets were derived from fatty acids of the monounsaturated (oleic acid) and saturated (capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid) variety. Despite what Mario and his snarling cheer squad would prefer to believe, the results of this study cannot even begin to be explained away by the consumption of inordinate amounts of n-6 PUFA; the amounts consumed in this study would easily be replicated by any pork-, poultry- and beef-fat-slurping low-carber.

So what does explain the reduction in T3 seen on the low-carb diet? Well, remember how I said that Dr. Bisschop and his team also measured urinary nitrogen excretion in the male subjects? Urinary nitrogen excretion is a long-standing and widely employed marker for protein (as in, lean tissue) breakdown. Low-carb diets have repeatedly been shown to increase nitrogen excretion, which is one reason why they suck the big one for building muscle. It’s also the most likely reason they also suck for maintaining optimal T3 levels. As Dr Bisschop stated in the passage I quoted earlier, the reduction in T3 appears to be an attempt by the body to try and at least partially counter the increase in protein breakdown that occurs on low-carb diets. The key mechanism behind this increased catabolism, by the way, is dramatically lowered insulin levels. Yep, insulin - that much maligned hormone that the low-carb fringe lunatics would have you believe is more evil than an Australian Labor-Green Party coalition - is actually helping you preserve your muscle mass and keeping your T3 levels at a healthy level. That’s a good thing.

Champion bodybuilder Branch Warren knows carbohydrates help build muscle, which is why he's been known to put away as much as 1000 grams of them daily!

Why the Volek Study Proves Absolutely Nothing About Thyroid Levels

It's now time to tear up what the PUFA theorists believe to be their trump card. The study headed by Jeff Volek  is the only one allegedly showing no change in thyroid hormone levels on a low-carb diet, so of course it is eagerly cited by Mario as proof that I’m wrong. Just one wee problem: Volek et al didn’t even measure levels of T3, the critical thyroid hormone in question! Instead, as I explained in my article, the pro-low-carb and Atkins-sponsored Volek team chose to only measure T3 uptake, a test also known as “resin-binding T3 uptake”.

This, of course, is just fine by Mario, who happily extrapolates the results of unrelated studies examining the relationship between thyroid hormones and a bunch of other hormones; studies, I should point out, that did not involve low-carb diets. This kind of fantasy-based commentary is par for the course in the world of low-carbia; when low-carb advocates cannot find the direct experimental results they are after, they take indirect and often totally irrelevant results and go ahead and extrapolate them in a manner that fits in nicely with their preconceived beliefs (hi Dr Mike!)

Sorry folks, but I’m having none of that nonsense here. Instead, let’s have a look at what might have happened had Volek et al bothered to measure not just resin-binding T3 but actual thyroid hormone levels as well. Otten et al did just that, comparing the following 1500 calorie diets:

I:   100% fat (F, 164 g; P, 5 g; CHO, 3 g);

II:  50% fat with 50%  protein (F, 82 g; P, 168 g; CHO, 7 g);

III: 50% fat with 50% CHO (F, 73 g; P, 6 g; CHO, 167 g);

IV:  Mixed diet (F, 70 g; P, 76 g; CHO, 137 g).

And here's what they found:

"Serum T4, TSH, T2, and T3-resin uptake did not change significantly during any of the experiments. Important changes, however, were noted in T3 and rT3, levels especially during periods I and II. These changes, as depicted in Table 2, equalled in diet period I (100% fat) the changes observed during total starvation in man."[Otten 1980]

So even though there was no change in T3 uptake, the two low-carb diets still decreased actual T3 to levels lower than that seen on the higher carb diets. In fact, on the highest fat diet, T3 levels fell to levels similar to those observed during starvation!

So what the Otten study shows is that the Volek low-carb subjects could indeed have experienced significant declines in T3 despite no changes in T3 uptake, but we’ll never know because the researchers conveniently chose not to measure the former. To use the Volek study as evidence that low-carb diets do not lower T3 levels is merely another exercise in extremely dodgey extrapolation.

Fifty Grams I Tell Ya, FIFTY GRAMS!!

If you look in the comments section of the article, you’ll see that “Stabby” cites the following study as evidence that only 50 grams of carbohydrate is needed to ensure blissful levels of T3:

Spaulding SW, et al. Effect of caloric restriction and dietary composition of serum T3 and reverse T3 in man. Journal of Clinical Endocrinology & Metabolism, Jan, 1976; 42 (1): 197–200.

Mario excitedly responds:

“And, if you look at the study cited by Stabby, in a severe calorie deficient diet, 50g (FIFTY GRAMS) of carbs was enough to restore T3 and rT3 levels. Based on this, how on the hell one can conclude that only a high carb diet is the best for thyroid?”

I’ll tell you how the hell, Mario. It’s by doing the very thing you low-carbers are so highly averse to; namely, examining the evidence in its entirety, as opposed to cherry-picking only the studies that can be twisted and distorted to support your case.

Let’s take a look at the Spaulding study. That paper reports that 800-calorie diets containing no carbohydrate (20 percent protein, 80 percent fat) mimicked the fall in T3 found during starvation. In contrast, the same subjects receiving isocaloric diets containing at least fifty grams of carbohydrate showed no significant changes in T3 levels. Mario and Stabby jump on this finding as if it is proof that only fifty grams of carbohydrate is needed to maintain optimal T3 levels. In doing so, they totally ignore the fact that this result was hardly a universal finding. They totally ignore all the other studies showing T3 reductions at higher carbohydrate intakes.

Ruth Mathieson and her colleagues from Virginia Polytech and State University placed fourteen obese free-living women on 530-calorie/day diets containing either 44 grams or 94 grams daily of carbohydrate. Both diets caused significant reductions in T3, with the ketogenic diet causing the largest decline[Mathieson RA].

Hmmm, the magical 50 grams – FIFTY GRAMS! – level cited by Stabby and Mario isn’t looking so magical after all. And the following studies indicate that the 50-100 gram level used as the cut-off for non-ketogenic dieting is no sure-fire guarantee of optimal T3 levels either.

Davidson et al found that increasing carbohydrate intake over a range of 104-409 grams daily at eucaloric levels resulted in greater T3 levels, while on the high-calorie diet T3 concentrations were similarly increased with carbohydrate intakes of 206 and 407 grams per day[Davidson MB].

Serog et al examined four isocaloric (mean intake 2800 calories/day) diets lasting 1 week each. In two of these, a standard diet containing 45 percent carbohydrate was consumed. The remaining two diets were either low- or high-carbohydrate, and were consumed by all the subjects in random order between the two standard diet phases.

Average carbohydrate intake in grams was 250 grams on the standard diet, 71 grams on the low-carbohydrate diet, and 533 grams on the high-carbohydrate diet. On the standard and high-carbohydrate diets, T3 levels did not change, ranging from 163.3 to 169.5 ng. They declined on the low-carb diet to a mean 148.6 ng. Mirroring these changes, rT3 rose significantly only on the low-carb diet[Serog P].

How the hell can I conclude a high-carb diet is best for the thyroid? Because that’s exactly what the research shows, Mario. In saying that, I want to make it perfectly clear that the kind of high-carbohydrate diet I recommend is one high in healthy carbohydrates. I’ve noticed a rather sneaky and disingenuous trend of late in which low-carbers are increasingly using the terms “high-carbohydrate” and “high sugar” interchangeably, as if they are the same thing. They’re not, and only a bloody idiot would try and claim that sucrose and fructose are the same as sweet potatoes, berries, and taro (more about bloody idiots in a moment).

When you examine the various studies, it is readily apparent that a wide variety of carbohydrate intakes were employed and yes, in a minority of cases no significant T3 reductions were observed at non-ketogenic low-carb intakes. No-one is saying that an exact % reduction in T3 will be noted at an exact specified number of carbohydrate grams. People vary far too widely in their biochemical individuality to make such a prediction. What is clear from the literature is a consistent pattern in which low carbohydrate intakes, be they ketogenic or non-ketogenic, produce significant declines in serum T3 levels, the effect being most pronounced on ketogenic diets. While not all people may experience overt symptoms of euthyroid sick syndrome (ESS), the literature clearly shows without a doubt that low-carb diets open the door wide for such symptoms to occur in susceptible individuals.

The ESS-inducing effects of low-carb diets are very real, and people need to know about them.’s “resident thyroid expert”, Mario Renato Iwakura, and the feral zealots of low-carbia may prefer to remain blind to them, but that doesn’t change the reality of their existence one iota. Since writing my article, I’ve had grateful emails from people who finally realized what was causing their low body temperature, cold intolerance, and general sluggishness. I’ve also had emails from people who sorely wished I’d written the article years earlier, as it would have saved them a lot of hassle and frustration. Of course, the low-carb camp doesn’t care about any of this; they prefer to simply ignore people who experience adverse effects on low-carb diets. Hear no evil, see no evil, right?

Wrong. Knocking low-carb hogwash to the ground since 2006.

Tormented Tessie

Before signing off, I want to address the aggrieved “Tess” who in her deluded rant in the comments section of Iwakura’s article states:

“Colpo is a bloody idiot. not the first time i’ve concluded this!…looking at his photo, i doubt that Anthony has any first-hand experience.”

Ah, you’re such a charmer, Tess. And such a liar.

In my Is a Low Carb Diet Bad For Your Thyroid? article, I discuss in detail my euthyroid sick syndrome issues while following a low-carb diet. This issue has very real relevance to me, because I suffered firsthand the low morning temperature and cold intolerance symptoms induced by low-carb dieting. I had to endure icicle-like extremities and rug up like the Michelin Man every damn winter for years on a low-carb diet, the problem only disappearing when I began eating a high-carb diet.

But Tess ignores this entirely, and falsely pretends I don’t have any first-hand experience with thyroid issues. Tess, like most of her low-carb cohorts, is a blatant and shameless liar. I just love the way low-carbers like Tess trumpet their own personal anecdotal experiences as inalienable truths that apply to everyone, but flat out ignore the anecdotal reports of (far more reliable) commentators who have had negative experiences on low-carb diets.

Tess, you’re a bloody idiot. Not the first time I’ve concluded this about a deluded, snarling low-carb cultist.

Can someone get Tess her teddy bear? She's just read the latest article, and not at all happy.

Tess, I know people like you like to look at those in good shape and flippantly dismiss their superior condition as the product of good fortune or some other unknowable, uncontrollable factor that for some mysterious reason you had the misfortune of not being blessed with. While this kind of rationalization no doubt helps you avoid some pretty discomforting introspection, it’s complete garbage. The real reason, my dear Tess, I kept lean despite suffering ESS is because I nevertheless obeyed the utterly inescapable reality of calories in versus calories out. I expended enough calories to maintain a low body fat level, low-morning temperatures and inferior low-carb dieting be damned. Instead of scowling and hissing like a spoilt little shit on Internet forums and blogs about my “slow thyroid”, I took the little bugger with me on my bike rides, whether it wanted to come along or not. Yep, while you and your low-carb ilk were pissing and moaning on the web with your “Oh woe is me, I have a retarded thyroid” carry-on, I was on my bike up in the Dandenong Ranges, clocking up the miles, chewing up the calories, and giving my lungs (and thyroid) a good tickle in the chilly winter air.

I know people want me to be ashamed of the fact that I’m not a lazy slob looking for an easy way to lose weight, for instead being a motivated person who actually enjoys working hard at something then subsequently reaping the rewards for it. I know we now live in a world where people are raised to believe they are entitled to anything and everything they want without having to put in any real effort, and taught to blame every single thing that’s ever gone wrong in their life on external factors, but too bad – I don’t subscribe to that bullshit, and if you low-carb folks ever want to amount to something more than a bunch of chubby, disgruntled, groaning Internet losers, you’d be well served to do the same.

The reality is that if people spent less time whining, wanking, and acting like pseudo-intellectual tossers on Internet forums and blogs, and instead got off their soft, fat asses and did some real vigorous exercise (angry keyboard tapping is not exercise), there’d be a lot less adipose tissue in the world. Not to mention a lot less annoying, aggrieved low-carbers with rattlesnake personalities rabidly angry at the world because Mother Nature didn’t endow them with the ability to look like Cindy Crawford despite sitting on their lazy butts all day.

And for the record, even Cindy Crawford exercises, so here’s a news flash: if a gifted gal like Cindy needs to exercise to keep in shape, you flabby Internet warriors certainly aren’t going to do it by remaining sedentary.

No, seriously!

"When I had my son, I did pretty much no carbs and it was effective for a short term, for getting rid of baby fat. But the truth is I didn’t feel as good. I felt almost depressed. It’s not sustainable; you can’t live your life not eating carbs." - Cindy Crawford, Slimming Magazine, June 2005.

You can endlessly talk and debate and wank on about acetyl-coenzyme-A-carnitine-transferase-uncoupling-protein-beta-agonist-Lolly-Gobble-Bliss-Bombs, but until you acknowledge the most simple fat loss fact of all – calories in versus out – and start burning the chub off with good honest exercise and sensible eating (as opposed to idiotic low-carb faddism) you will never get lean. I know MMA fighters, cyclists, bodybuilders and runners who wouldn’t have a clue what an “uncoupling protein” is, and if asked what “COA” stands for would probably venture “Certificate of Authenticity” instead of Coenzyme A. But guess what? They’re all leaner and fitter than you, and have body fat levels that would put virtually every low-carb and Paleo guru to complete shame. Why? Because they don’t talk the talk – instead they get off their butts and walk the walk. They train hard and consistently, and they watch what they put into their mouths. They are conscientious individuals who take responsibility for their physical condition, and know full well the physical results they strive for will never be achieved by sitting at a computer selectively wanking on about metabolic minutiae.

I can already hear the self-righteous howls of protest at what I’ve just written, but telling the plain truth is always a sure fire way to piss people off. Sorry folks, but at no point in time did I say I was here to piss in your ear and tell you everything you want to hear. If you don’t like my style, there’s always that little red box with the cross at the top right corner of your screen…

As you’re leaving, here’s something for you to ponder: This “bloody idiot” is far leaner than any of the low-carb geniuses who so vehemently insist I’m full of baloney.




PS. Jay, congratulations on the continued fat loss! You’re living proof that those who abide by the scientific principles outlined in The Fat Loss Bible achieve far more than the sad malevolents who childishly and fruitlessly rebel against me and said principles. Like I said here folks, if you can’t beat me, join me … 🙂


Bisschop PH, et al. Isocaloric carbohydrate deprivation induces protein catabolism despite a low T3-syndrome in healthy men. Clinical Endocrinology, 2001; 54: 75-80.

Davidson MB, Chopra IJ. Effect of carbohydrate and noncarbohydrate sources of calories on plasma 3,5,3′-triiodothyronine concentrations in man. Journal of Clinical Endocrinology & Metabolism, Apr, 1979; 48 (4): 577–581.

Mathieson RA, et al. The effect of varying carbohydrate content of a very-low-caloric diet on resting metabolic rate and thyroid hormones. Metabolism, May, 1986; 35 (5): 394-398.

Otten MH, et al. The Role of Dietary Fat in Peripheral Thyroid Hormone Metabolism. Metabolism, Oct, 1980; 29 (10): 930-935.

Serog P, et al. Effects of slimming and composition of diets on V02 and thyroid hormones in healthy subjects. American Journal of Clinical Nutrition, Jan 1982; 35: 24-35.

Anthony Colpo is an independent researcher, physical conditioning specialist, and author of the groundbreaking books The Fat Loss Bible and The Great Cholesterol Con. For more information, visit or

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