Optimize protein intake for testosterone, thyroid and muscle growth

Is meat bad for testosterone and thyroid hormone production?

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TLDR: Protein doesn’t negatively affect testosterone or thyroid function. The different amino acid profiles of different protein sources can differently affect thyroid hormone-binding proteins, which can modulate the free T3 fraction.

Hypothyroid individuals would do better to avoid pork and duck (maybe turkey and chicken as well) and stick to lamb (and maybe beef and whey as well).

Apart from the amino acids, animal foods are the best source of micronutrients, which is extremely important for thyroid hormone and testosterone production.

The best range for testosterone and thyroid optimization is likely around 20-35% of total calories, or 1.6-2.4g/kg/BW.

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Table of Contents

Protein consumption has been studied a lot for longevity and thyroid hormone production.

Should we be limiting our meat intake or does it not really matter?

I argue that there isn’t any good evidence to limit meat intake to improve thyroid hormone or testosterone production and on the contrary, evidence rather points to at least having a certain amount of animal foods in your diet since they provide valuable compounds you don’t get anywhere else.

Protein intake and testosterone

There is this very famous study that gets cited all the time that high-carb diets are better for improving testosterone than high-protein diets.

Let’s take a closer look. Here are the details. They compared a high carb diet (10% protein, 70% carbs and 20% fat) to a high protein diet (44% protein, 35% carbs and 20% fat) in 7 men while eating at maintenance for 10 days.

The results: “Testosterone concentrations in seven normal men were consistently higher after ten days on a high carbohydrate diet (468 +/- 34 ng/dl, mean +/- S.E.) than during a high protein diet (371 +/- 23 ng/dl, p less than 0.05) and were accompanied by parallel changes in sex hormone binding globulin (32.5 +/- 2.8 nmol/l vs. 23.4 +/- 1.6 nmol/l respectively, p less than 0.01). By contrast, cortisol concentrations were consistently lower during the high carbohydrate diet than during the high protein diet (7.74 +/- 0.71 micrograms/dl vs. 10.6 +/- 0.4 micrograms/dl respectively, p less than 0.05), and there were parallel changes in corticosteroid binding globulin concentrations (635 +/- 60 nmol/l vs. 754 +/- 31 nmol/l respectively, p less than 0.05).” (R)

Not even a 100ng/dl change.

There are a couple of downsides here.

  • They only used 7 men.
  • They did the study for only 10 days.
  • They didn’t check testosterone before the diet, so they have no idea how each individual’s testosterone changed.
  • They drew blood from 8am to 8pm every 2 hours. So they got a total of over 12 hours and we know testosterone varies significantly over the day. That’s not how it’s done in almost all other studies, where blood is only drawn in the morning.

But let’s say this study is not garbage. Perhaps the high-carb diet group’s T would have gone even higher over time. Perhaps it would have started to go down because they were not getting enough micros. We don’t know, but this study is a far cry to start recommending low protein, high carb diets to people to optimize their testosterone.

Let’s move on.

This meta-analysis found that moderate-protein intake of less than <35% of total calories), low-carbohydrate diets had no consistent effect on resting total testosterone. However high-protein intake of over 35% of total calories, low-carbohydrate diets greatly decreased resting and post-exercise total testosterone (R).

As long as you stay below 35% of your total calories from protein, your testosterone should be fine.

During a 40% deficit (which is a very big deficit), there is no difference in testosterone between 0.8 (RDA), 1.6 (2×-RDA), and 2.4 (3×-RDA) g/kg/d for 31 days (R).

This good 1-year study found that a higher protein low fat (35% protein, 40% carbohydrate, 25% fat) or higher carbohydrate low-fat diet (17% protein, 58% carbohydrate, 25% fat) diet increased testosterone after a 12-week deficit as well as after a 40-week maintenance phase with no difference between the two groups (R).

In summary, stick to below 35% of your total calories from protein during maintenance or bulking. During a cut, you can go as high as 2.4g/kg/BW, which will be enough to retain your muscle mass without negatively affecting testosterone levels.

Protein, micros and testosterone

Animal food sources are the best sources of micronutrients, such as zinc, iron, selenium, calcium, fat-soluble vitamins, B-vitamins, magnesium, etc. If you want to limit protein intake under the false assumption of longevity, you might be missing out on a lot of beneficial T-boosting micros.

Let’s switch over to thyroid function

Protein intake and thyroid

Some people think that protein suppresses thyroid hormone production and thyroid hormones are essential for steroidogenesis. Hypothyroid individuals tend to have lower T than euthyroid individuals.

Thyroid hormone T3 is also one of the most potent 5-alpha reductase inducers.

So you clearly don’t want to negatively affect your thyroid right?

Is it best to avoid meat then? Is it really bad?

Let’s dive in!

Amino acids and thyroid hormone production

Some studies (not all) in the past have shown that higher protein intake in animals lead to lower levels of thyroid hormone.

But I’d like to bring attention to the fact that it’s rather the free fraction (free T3) that is sometimes lower, and not total T3. And this all depends on the kind of protein consumed.

We conclude that while serum total T3 is elevated in rats chronically fed a low protein diet, this elevation is not due to enhanced T4 to T3 conversion. Rather, the increased T3 levels can be accounted for by a striking alteration in protein binding to T3.” (R)

Different kinds of protein (beef, lamb, pork, chicken, turkey, casein, whey, etc) have different amounts and ratios of amino acids.

And the reason why this is important, is because higher levels of certain amino acids boost certain thyroid hormone carriers, such as thyroid hormone-binding globulin (TBG) and albumin.

Amino acids and thyroid hormone-binding proteins

Glutamic acid, leucine, aspartic acid, serine, and alanine correlate with TBG, thus eating meat high in those amino lead to higher TBG.

Isoleucine, and particularly leucine can promote albumin synthesis.

Transthyrethin (TTR) is also an important protein carrier for the thyroid hormones
(binding 5% of serum T3 and 20% T4) and serum TTR concentrations are particularly correlated with serum valine levels.

In summary, different kinds of meat have different amino acid amounts that can differently affect thyroid carrier proteins. As per the table above, even a small difference in the amount of amino acids can make a large difference in total thyroid carrier proteins.

Here are a few examples:

Duck meat increased TBG (compared to casein) which lowered fT3, but not total thyroid hormone production (R).

Pork meat (PM) consumption increased total serum tri-iodothryonine (T3) concentrations (P < 0.05) and decreased serum thyroxine (T4) concentrations compared to casein and lamb meat (LM). However, the PM group had the lower fT3 due to the greatest increase in thyroid carriers, namely TBG and serum albumin. Consequently, pork meat leads to the highest T3 (due to having the highest selenium content), but the lowest free T4 and fT3 compared to casein and lamb (R).

On the other hand, lamb meat consumption lead to a decrease in serum albumin, which increased fT3 which lead to an increase in energy expenditure (R).

As you can see from the image below, the pork diet group had the biggest DIO (the enzyme which converts T4 into T3).

As you can see from this table below, all groups got an increase in T3, with pork diet being the most. However, fT3 decreased in the pork diet, but increased the most in the lamb diet.

In Eastern food cultures, meat is thought to provide an additional physiological benefit beyond that of meeting basic nutritional needs of functional foods. Using meat for health purposes rather than for nutrition alone opens up a whole new field for the meat industry (R).

Some researchers believe that lamb consumption provides health benefits such as enriching blood quality, leading to higher energy levels, while pork consumption provides different health benefits, such as having a cooling effect on the body (R).

This makes lamb a great food for the winter or for hypothyroid individuals and pork is a great food for the summer when you want to cool off.

Lastly, this study found that giving animals escalated doses of whey dropped their TSH and increased their T3 with each increase in whey.

Result: thyroid hormone T4 (0.7–1.48 ng/dL) and T3, and thyroid hormone synthesis parameters including intrafollicular colloid amount, follicular diameter, and epithelial height were significantly higher in 3 cc and 5 cc IHWP (ısole hydrolyzed whey protein) groups compared to the control. Conclusion: We think that regular daily use of IHWP may increase the synthesis of thyroid hormone due to its high amino acid content.” (R)

People want to avoid meat for the “harmful thyroid-lowering” sulfur amino acids, methionine and cysteine since they inhibit thyroid peroxidase. Thyroid peroxidase oxidizes iodide ions to form iodine atoms for addition onto tyrosine residues on thyroglobulin for the production of thyroxine (T4) or triiodothyronine (T3), the thyroid hormones. However, the inhibitory effect can be overcome by adding more iodide (R).

Additionally, despite pork having very high cysteine, methionine and tryptophan, it still increased T3 the most. These amino acids aren’t that big of a problem when found in the food matrix. Micros and amino acids that increase binding proteins matter more.

Despite pork being second highest, the pork group had the highest T3, due to the high selenium content. However, the lowest fT3, due to amino acids enhancing the synthesis of albumin.


Hypothyroid individuals would do better to avoid pork and duck (maybe turkey and chicken as well) and stick to lamb (and maybe beef and whey as well).

Many studies have found that higher meat/protein consumption increases T3, energy expenditure, thermogenesis and satiety in animals (there are no human studies on this) (R, R, R, R). I’m not trying to make the case that everyone should be eating massive amounts of protein daily, but between 100-200g daily is a good goal to shoot for depending on body weight and activity level.

As a side note, a low level of protein in the diet combined with iodine excess evoked a more extensive cellular damage of the thyroid gland than iodine overdose alone (R). A lot of food (not to mention salt) is enriched with iodine and a lot of people don’t eat nearly enough protein. It’s likely that a lot of people are overconsuming iodine with inadequate protein. This leads to thyroid damage and a drop in thyroid hormone.

This study found that people with Hashimoto’s thyroiditis tended to consume more processed meat (which is usually very high in iodized salt), whereas the control consumed more red meat (R).

A neat little trick if you want to increase free T3 is to use aspirin or sodium salicylate. Salicylate displaces T3 from TBG and increases fT3 and T3 uptake (R, R).

Protein sources, micronutrients and thyroid function

As you’ve seen above, selenium boosts T4 and T3 production. Meat that is high in selenium, such as pork, will increase T3.

Point is, that micros are very important for proper thyroid function. If you don’t eat a nutrient-dense diet, where will you get your micros? Plants? They are full of anti-nutrients and in no way better than animal foods.

Some would argue that if you have a fast metabolism you can retain your micros better. But how will you get a fast metabolism without micros? CoQ10 for example essential for proper energy production and a fast metabolic rate. Where do you get CoQ10? Animal foods!

In order for the thyroid to produce nutrients sufficiently, it requires nutrients, namely zinc, selenium, iron, calcium, B-vits (flavoproteins, ), etc.


We can all agree that excess iron is bad, but we do need a certain amount of iron. The best food source of iron is red meat, which is about 4 times higher in iron than white meat and 10 times higher in heme iron than white meat.

The central role that iron has in thyroid economy can be explained by one good reason: thyroid peroxidase (TPO) is a hemeprotein. Experimental data have shown that iron deficiency reduces the activity of TPO (R). Additionally, iron deficiency can lead to decreased plasma concentrations of T3 and T4 and increased hepatic rT3 deiodination, suggesting that iron deficiency tends to metabolize thyroid hormones via deactivating pathways (R).

Heme is produced in mitochondria and the path into these organelles requires coordinated action between intestinal uptake or iron, iron transport and entry into the cytoplasm and into the mitochondria. Besides iron other nutritional requirements for heme synthesis include: vitamin B6, riboflavin, biotin, copper and zinc (R). And those nutrients you also get abundantly in animal foods.


Low levels of zinc can (R):

  • Lead to low T4 and T3. In patients with Down syndrome, supplementing with Zn sulfate can improve thyroid function (R).
  • down regulate the activity of the TRH degrading enzyme in the hypothalamus and pituitary, leading to increased levels of TSH and prolactin.

Low levels of Zn have been described as being related to uncoupling of mitochondrial function acting at the level of cytochrome b and c interfering also with CoQ10 (R).


Magnesium is crucial for thyroid iodine uptake as well as ATP production. ATP synthesis appears to be essential for iodide uptake to occur (R).

Magnesium deficiency can reduce the bioavailability and tissue distribution of selenium which can also negatively affect thyroid hormone production and conversion.

Many hypothyroid symptoms are the same as low magnesium symptoms. This study claims that: “Dwelling deeper into this clinical situation we were able to identify a common denominator behind the “so-called” thyroid disease complex of symptoms, namely magnesium deficiency [15].” (R)

It is a common clinical observation that some otherwise healthy patients with hypothyroidism continue to complain of fatigue, poor mood, inability to concentrate, and vague cognitive difficulties (often described as “brain fog”) despite normal TSH levels” (R)

Giving them magnesium can reduce those symptoms. As you can see from the graph above, a drop in magnesium can actually increase fT4, which could give you the idea everything is going well. But in reality, fT3 is likely dropping leading to hypothyroid symptoms.

Stress (e.g. sound, seasonal, darkness, physical, financial, relationship, traffic, etc.) can powerfully deplete magnesium and lead to hypothyroid symptoms. “The importance of psychological stress has to be considered and treated in all cases of thyroid disease.” (R)

Vitamin B2

Riboflavin plays a role in the process of thyroid hormone deiodination in the form of flavoproteins. Flavoproteins use nicotinamide adenine dinucleotide phosphate (NADPH) and FAD (created from riboflavin) for the generation of H2O2. H2O2 is indispensable for thyroid hormone synthesis.

Thioredoxin reductase, a flavoprotein, plays an important role in the response to iodine excess. What are the best sources of riboflavin? Milk and organ meat.


The thyroid gland is particularly rich in selenium, which takes part in the structure of antioxidant enzymes (e.g., glutathione peroxidase—GPx—and thioredoxin reductase—TrxR—as well as the three deiodinases—D1, D2, D3). Specifically, these proteins retain a key role in hormone metabolism and a powerful antioxidant activity directed against free radicals generated during the production of thyroid hormones (R). Too little selenium can lead to excess oxidative stress in the thyroid as well as a reduction in T3 levels.

Sustained physical and psychological stress in men has been shown to induce lower levels of zinc, iron, and selenium. Both the structure, i.e. loss of cristae, and the electron transport function of mitochondria can be altered in selenium deficiency. Finally, selenoprotein synthesis is also an active process that requires ATP, and proper ATP production requires magnesium and CoQ10.

Point being, eating animal foods rich in these micros is key to improving thyroid health and hormone production.


Protein doesn’t negatively affect testosterone or thyroid function. The different amino acid profiles of different protein sources can differently affect thyroid hormone-binding proteins, which can modulate the free T3 fraction.

Hypothyroid individuals would do better to avoid pork and duck (maybe turkey and chicken as well) and stick to lamb (and maybe beef and whey as well).

Apart from the amino acids, animal foods are the best source of micronutrients, which is extremely important for thyroid hormone and testosterone production.

The best range for testosterone and thyroid optimization is likely around 20-35% of total calories, or 1.6-2.4g/kg/BW.

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