An underactive thyroid is a common disease in society and can affect up to 5 percent of the population with numbers estimated to be even greater in the coming years as over one-third of the world currently lives in areas with iodine deficiencies . You can start suspecting that you may have an underactive thyroid if you start to notice some of the classical symptoms of cold intolerance, weight gain, irritability, hair loss and memory problems . Unfortunately, most patients do not present with such textbook presentations and may have a variety of other symptoms that can steer doctors in different directions when trying to make a diagnosis. These patients may first present to their general practitioner's office with complaints of infertility, constipation or chronic diarrhea . As you can see now already, there is a wide spectrum that can be associated with an underactive thyroid but can your diet be a key to helping cope with these strange symptoms?
Benefits of a Gluten-Free Diet with Hypothyroidism
When you are finally diagnosed with an underactive thyroid, it may just be the "tip of the iceberg" for you when it comes to uncovering a number of other diseases that may be linked with your hypothyroidism. Hopefully, by the end of this article, you do not become a full-fledged hypochondriac but an underactive thyroid is often linked with a number of other auto-immune diseases that could come in tandem . This could range from diseases like rheumatoid arthritis (RA), Celiac Disease and even lactose intolerance. Patients that have autoimmune hypothyroidism have a 5 percent chance to have overt Celiac Disease as well . Because of a similar genetic mutation that predisposes patients to thyroid problems, patients may have a different spectrum of disease presentation and even if they are not diagnosed with Celiac Disease directly, may have bowel problems due to their thyroid dysfunction.
This diet is not enough when it comes to managing your thyroid dysfunction, however. In one study, participants who were recently diagnosed with Celiac Disease were tested to see if they had an underlying thyroid problem. About 33 percent of patients diagnosed with celiac disease had thyroid dysfunction compared to only the 5 percent of the population without celiac disease. Participants were then instructed to consume a gluten-free diet and at the conclusion of the study, it was found that the thyroid volume had decreased after one year in these candidates. This finding demonstrates that with just diet alone, the thyroid function will get worse if more aggressive therapies (like medication) are not implemented. 
Benefits of a Casein-free Diet with Hypothyroidism
As you learned from the last section, a gluten-free diet will help you with your thyroid dysfunction to manage your symptoms but should not be used as a single treatment method for your underactive thyroid.
As we learned from a previous article, dietary changes do show that patients improve their symptoms and if they switch to a strict vegetarian diet, there was some quantitative evidence that their thyroid function improved to the point of no longer needing supplemental medication.
Casein is a popular compound in modern society and may be more familiar to some of our readers if it is called the slow-digested "whey protein." This is a milk-based protein that helps gym enthusiasts to build muscle naturally without the use of steroids. In the medical world, it has also received a lot of attention as it has been linked with increasing the aggressiveness of prostate cancer .
This is exactly the same mechanism that happens when patients have autoimmune thyroiditis so it is better to not aggravate the problem any further. This same study found that once protein was re-introduced into the diet, the thyroid function improved and the gland shrunk in size. 
In another interesting study, patients with Hashimoto's thyroiditis (autoimmune thyroiditis) were tested to determine if they had lactose intolerance (another milk protein like casein) and it was found that 75 percent of participants had an underlying lactose intolerance as well!
As you can see, casein and lactose are two tricky proteins to deal with when providing recommendations for protein restriction in diets. Patients will benefit from some type of protein like casein to have iodine delivered to your thyroid to improve its function. However, if a patient also has an underlying lactose intolerance, the best thing to do is to avoid milk proteins entirely and substitute your diet for other types of healthy proteins.If you have an underactive thyroid, make sure you ask your doctor for additional autoimmune disease testing before your start your hypothyroid diet.