Is Your Diet Negatively Affecting Your Thyroid?

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When I addressed the issue of the theory of “Safe Starches” as outlined in the “Perfect Health Diet” book, a couple of months ago, one of the reasons given by Paul Jaminet for eating a certain amount of starches, was that being low-carb for too long can negatively affect thyroid function. I didn’t really think about it too much at the time, but since then I’ve been revisiting the idea. I’ve noticed for a while now, that even though the majority of my body is quite lean, I still can’t seem to get rid of the little amount of fat left on my belly and love-handle area. Could it be that my belly persistent belly-fat is because after many months spent on a very-low-carb version of the Paleo Diet, I’ve reduced the effectiveness of my thyroid, and over-produced cortisol?

Last year, on the 18th of August 2011, Paul Jaminet published an article on the website, called “Low Carb High Fat Diets and the Thyroid”. Paul opened with the following statement:

There have been anedoctal reports on low carb forums about people becoming hypothyroid after following a low carb, high fat diet. Anthony Colpo recently wrote a blog post about carbohydrate, fat and protein intake and their effects on thyroid hormone levels, concluding that a high fat or high protein diet is detrimental and that a high carbohydrate diet is good for the thyroid [].

What I will try do demonstrate here is that the sole conclusion we can draw from the literature, including the studies cited by Anthony and others, is that a high polyunsaturated fat (PUFA) diet is detrimental to thyroid health. There is no evidence that a diet, such as the Perfect Health Diet, that is high in saturated and monounsaturated fat, low in PUFA, and provides sufficient, moderate levels of protein and carbohydrate, has any detrimental effect on the thyroid. On the contrary, I believe that such a diet is optimal for thyroid health.”

Paul went on to point out that he majority of the studies on the subject, including most of the studies that were cited by Anthony Colpo, used only polyunsaturated fats as the primary source of fat, in the “high-fat” portion of the studies. Paul showed that the studies that included a high amount of PUFAs, all led to suppressed thyroid function.

Low-PUFA High-Fat Diets and the Thyroid: Lack of Direct Evidence

Unfortunately we don’t have human studies comparing diets high in saturated fat and polyunsaturated fat and their effect on thyroid hormones synthesis. Neither do we have studies showing what happen to T3 levels after a high saturated/monosaturated fat diet is eaten. We will have to rely on indirect evidence.”

“So the high-PUFA diet promoted weight gain: it caused excess weight to be retained at a lower calorie intake. This is consistent with reduced thyroid activity.

Is this effect due to a high-fat diet generally, or to high-PUFA diets only? Some insight into this question may be found in a blog post by Stephan Guyenet []. Rats fed isocaloric diets in which the fat source was varied among three groups – a beef tallow group (primarily saturated fat, 3% PUFA), an olive oil group (primarily unsaturated, 10-15% PUFA), and a safflower oil group (78% PUFA) – had highly variable weight gains. The olive oil group gained 7.5% more weight than the beef tallow group, and the safflower oil group 12.3% more weight.  This is exactly the same pattern found in the Vermont overfeeding study in man: reduced energy expenditure as the consumption of PUFA increases.”


A diet with sufficient but not excess protein, moderate carbohydrate comprising a minority of calories, and high intake of saturated and monounsaturated fat but low intake of polyunsaturated fat would seem to be optimal for thyroid function. But this is the Perfect Health Diet!”

Well of course Paul concludes that the findings were consistent with the diet that he peddles, but it actually appears to be the truth in this case.

Just from looking at the data, it is definitely obvious to me that a very-low-carbohydrate diet, coupled with a high intake of polyunsaturated fatty acids (PUFAs), is a recipe for thyroid disaster. However, it does appear that a higher-fat, moderate protein, and moderate carbohydrate diet that focuses on saturated fats, and not PUFAs will optimize most of these thyroid factors.

So, is your diet negatively affecting your thyroid? Personally, I think that It’s definitely time for me to up the carbs, and reduce the amount of PUFAs that I’m eating. I hate to say it, but that could mean saying goodbye to most of the bacon I eat! But what about the carbs? Should I use the PHD signature “safe starches”, or is there a potentially “better” choice for my carb intake? Maybe I’ll cover that in my next article….

Have you found it difficult to lose those last pounds and inches while following the Paleo diet? Please leave your comments, questions and observations below. If you found this article interesting please share it on your social media network. Thank you!


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Barry Cripps is a Paleo-based Nutrition and Wellness Consultant, who operates out of Bowling Green, Kentucky.

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