It’s crazy when you think about all of the different kinds of food we eat.
We just swallow and hope it all works out for the best.
Well, it turns out there are better ways
to think about keeping our bodies humming healthfully along.
Welcome to Nutrition Facts.
I’m your host Dr. Michael Greger.
Did you know that the mighty thyroid controls your metabolism,
produces hormones, and helps regulate your body temperature?
What can we do to support it?
Let’s start with a story about plant based milk and iodine.
Adequate dietary iodine is required for normal thyroid function.
In fact, the two thyroid hormones are named after how many
iodine atoms they contain: T3 and T4.
Now, given that iodine is extensively stored in the thyroid gland itself,
it's not something you have to get every day,
but your overall diet needs to have some good source.
Unfortunately, the common sources aren't particularly health-promoting:
iodized salt, [and] dairy foods
because iodine-based cleansers like betadine are used to sanitize
the udders, which results in some iodine leaching into the milk.
They also add iodine to cattle feed,
and some commercial breads have iodine-containing food additives.
So if you put people on a paleo-type diet and cut out dairy and table salt,
they can develop an iodine deficiency, even though they double
their seafood intake, which can also be a source.
What about those switching to diets centered around whole plant foods?
They're also cutting down on ice cream and Wonder Bread,
and if they're not eating anything from the sea—seaweed, sea vegetables—
they can run into the same problem.
Her parents reported striving to feed her only the healthiest foods.
The 3-year-old only got plant-based, unsalted, unprocessed foods
with no vitamin supplementation. Now that could have been deadly.
With no vitamin B12, those on strictly plant-based diets can develop
irreversible nerve damage, but in this case, a goiter arose first
due to inadequate iodine intake.
Here's another case of veganism as a cause of iodine deficient
hypothyroidism in a toddler after weaning. Now before weaning,
he was fine because his mother kept taking her prenatal vitamins,
which luckily contained iodine.
Most vegetarians and vegans are apparently unaware of the importance
of iodine in pregnancy, just as clueless as their omnivorous counterparts.
The American Thyroid Association and the American Academy of Pediatrics
have recommended that women even just planning on getting pregnant
should ingest a daily supplement that contains 150 micrograms of iodine, yet
only 60% of prenatal vitamins marketed in the US contain this essential mineral.
So, in spite of the recommendations, about 40% lack it. Therefore, it's
extremely important that pregnant and breastfeeding women read the labels
to ensure they're receiving an adequate amount.
Women of reproductive age have an average iodine level of 110,
which is fine for nonpregnant individuals, but we'd really
like to see at least 150 in pregnancy.
It's basically a 24-hour urine test, in which iodine sufficiency is defined
as 100 mcg/liter of pee in nonpregnant adults, which your average vegan
fails to reach in the largest study done to date, out of Boston.
The recommended average daily intake is 150 mcg/day for most people,
which you can get in like a cup and a half of cow's milk.
Sadly, plant-based milks are typically not fortified with iodine,
averaging only about 3 mcg/cup. In the largest systematic study to date,
although many plant-based milks are fortified with calcium, they only found
just 3 of 47 fortified with iodine.
Those that were had as much as cow's milk, but those that weren't fell short.
Plant-based milk companies brag about enriching their milks with calcium,
and often vitamin B12, D, and vitamin A, but only rarely are attempts made
to match the iodine content.
The only reason cow's milk has as much as it does is that they enrich
the feed, or it comes dripping off their udders.
So why don't plant-milk companies add iodine, too?
I was told by a food scientist at Silk that my carrageenan video
played a role in them switching to another thickener.
Hopefully, they'll see this video and consider adding iodine, too,
or some company will snatch at the market advantage opportunity.
The researchers conclude that individuals who consume plant-based milks
not fortified with iodine may be at risk for iodine deficiency,
unless they consume alternative dietary iodine sources,
the healthiest of which is sea vegetables, which we'll cover next.
Dairy milk supplies between a quarter and a half of the daily iodine requirement
in the United States, though milk itself has little native iodine.
The milk iodine content is mainly determined by factors like
the application of iodine- containing teat disinfectants.
The iodine residues in milk appear to originate
mainly from the contamination of the teat surface.
The teats are sprayed or dipped with like betadine-type disinfectants,
and the iodine just kind of leaches into the milk.
Too bad most of the plant- based milks on the market
aren't enriched with iodine, too.
Fortified soy milk is probably the healthiest of the plant milks,
but even if it was enriched with iodine, what about the effects of soy
on thyroid function?
It's funny, when I searched the medical literature on soy and thyroid,
this study popped up:
a cost-effective way to train residents to do thyroid biopsies.
Just stick the ultrasound probe right on top and go to town.
It turns out on ultrasound your thyroid gland looks a lot like tofu.
Anyway, the idea that soy may influence thyroid function
originated over eight decades ago when marked thyroid enlargement was seen
in rats fed raw soybeans, though the observation that people living in Asian
countries have consumed soy foods for centuries
with no perceptible thyrotoxic effects certainly suggests their safety.
The bottom line is there does not seem to be a problem
with people who have normal thyroid function.
However, soy foods may inhibit the oral absorption of Synthroid,
thyroid hormone replacement drugs, but so do all foods.
That's why we tell patients to take it on an empty stomach. But you also
have to be getting enough iodine, so it may be particularly important
for soy food consumers to make sure their intake of iodine is adequate.
What's the best way to get iodine? For those who use table salt,
make sure it's iodized.
Currently, only half of table salt sold contains iodine,
and the salt used in processed foods is typically not iodized.
Of course, ideally, we shouldn't add salt at all.
Dietary salt is a public health hazard. Think this title is a little over the top?
Dietary salt is the #1 dietary risk factor for death on the planet Earth,
wiping out more than three million people a year
twice as bad as not eating your vegetables.
What's the best source of iodine, then?
Sea vegetables! You can get a little iodine here and there
from a whole variety of foods,
but the most concentrated source by far, with up to nearly 2,000%
of your daily allowance in just a single gramâ€”
which is like the weight of a paperclip: seaweed.
Given that iodine is extensively stored in the thyroid, it can be safely consumed
intermittently, meaning you don't have to get it every day,
which makes seaweed use in a range of foods attractive,
and occasional seaweed intake enough to ensure iodine sufficiency.
However, some seaweed should be used with caution
due to its overly high iodine content, like kelp.
Too much iodine can cause hyperthyroidism,
a hyperactive thyroid gland. A woman presented
with a racing heartbeat, insomnia, anxiety, and weight loss
thanks to taking just two tablets a day containing kelp.
In my last video, I noted how the average urinary iodine level of vegans
was less than the ideal levels, but there was one kelp-eating vegan
with a urinary concentration over 9,000.
Adequate intake is when you're peeing out 100 to 199.
Excessive iodine intake is when you break 300; 9,437: way too much.
The recommended average daily intake is 150 mcg/day for non-pregnant,
non-breastfeeding adults, and we may want to stay below 600 on a day-to-day basis,
whereas a tablespoon of kelp may contain 2,000.
I'd stay away from kelp because it has too much,
and stay away from hijiki because it contains too much arsenic.
Here's how much common seaweed preparations should give you
an approximate daily allowance: two nori sheets, you can literally
just nibble on them as snacks like I do;
one teaspoon of dulse flakes, which you can just sprinkle on anything;
one teaspoon of dried arame, which is great for like adding to soups;
or one tablespoon of seaweed salad.
If iodine is concentrated in marine foods, this raises the question
of how early hominins living in continental areas could have met
their iodine requirements.
Well, here's what bonobos do, perhaps our closest relatives.
During swamp visits, they all forage aquatic herbs.
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