Cooking & Baking

I spent the last couple of hours reading peer-reviewed papers and my take-away is that most of the thyroid medication is absorbed in your GI tract within 30-60 minutes, but some absorption can continue for another three hours after. Some studies differentiate between foods you can potentially have in that first period, but overall it's better to not have any. And definitely avoid the foods you're warned against during the first hour, and maybe even the first four hours.

The warning about those foods is in the Synthroid package insert (https://www.accessdata.fda.gov/drugsatfda_docs/label/2008/021402s011lbl.pdf):

Several sources indicated they just couldn't find testing to back up the warning about walnuts, but these are good examples of what I was reading -- Levothyroxine Interactions with Food and Dietary Supplements–A Systematic Review. I also read some good-quality patient resources like Do Walnuts Really Interfere with Synthroid Effectiveness? and I take levothyroxine (Synthroid), a thyroid hormone to treat hypothyroidism. Are there supplements or foods I should avoid, or be taking, due to this drug?.

I haven't seen anything that indicates I have to cut those foods out of my diet entirely. I've had my thyroid prescribed by five different physicians over the last 35-ish years, including an Endocrinologist, and they all indicated to take it on an empty stomach and avoid anything except coffee or tea for the first hour. Nothing about an overall dietary change. My sister takes her levothyroxine with a cracker, because her stomach needs that. Sure, that affects the absorption, but she takes the same cracker and the dose is calibrated to her TSH levels.

Unfortunately for me, I learned that, really, coffee and tea affect absorption, too. The study for that said that using coffee or espresso to down your pill was the worst, and it was less bad just have it later on in the 30-60 minute window. The latter is what I tend to do, and I'll think about it, but that's what I'll probably continue to do since that's how my dose is calibrated. If I change my habits, then I'll do so 6-8 weeks before my next thyroid check, so my dose is calibrated to my new habit.

Other interesting studies: Rats that are fed a diet with 20% soy meal have decreased thyroid output (though they may have also reduced their iodine intake, wasn't clear). Note that for a 2000-calorie diet, you'd have to consume 1.5 pounds of tofu every day to have 20% of your calories come from soy. None of the vegans I know come close to that. And if one of them is taking thyroid supplementation, then the dose is already calibrated to their situation.

Even in this study (The effect of soy phytoestrogen supplementation on thyroid status ...) where overall soy intake impacted human thyroid output, the conclusions note that soy has good effects on overall health ("soy phytoestrogen supplementation significantly reduces the insulin resistance, hsCRP, and blood pressure in these patients" ).

Overall, I don't see where your doc is coming from, if what he intended was an overall prohibition on those foods. Avoiding at breakfast, sure. But occasionally at breakfast? IMO, if your overall diet is the same as usual in the six weeks leading up to a thyroid check, then your thyroid dose will get calibrated to your situation. I'm not a doctor, though, so maybe ask him to clarify.