Eating selenium-rich foods is an excellent way to manage your thyroid health and prevent colorectal cancer, so knowing which foods are best is important!
Selenium is an essential micronutrient for the body, and this chemical element bears the symbol Se. A deficiency in this mineral can lead to hypothyroidism, as well as fatigue and other unwanted symptoms. While having a deficiency in selenium is unusual, particularly if you eat a balanced, healthy diet, there are certain situations in which your body may not properly absorb or metabolize this nutrient. A lack of this nutrient is also more common in those of significantly advanced age.   
In terms of how much selenium we should consume each day, 55 micrograms are recommended for adults, but this may vary slightly depending on your country of origin. Areas, where the soil is low in selenium, may have a higher occurrence of this deficiency.
Selenium – Rich Foods
The best selenium-rich foods include brazil nuts, halibut, cheese, mushroom, oat, oyster, asparagus, soybeans, chia seeds, salmon, brown rice, crabs, spaghetti, cabbage, broccoli, spinach, milk, yogurt, cashew, banana, garlic, tofu, turkey, pork, cod, spinach, wheat, and barley, among many others. 
With more than 540 micrograms in 1 ounce of Brazil nuts, these are some of the best sources of this mineral. 
At 47 micrograms per serving, this fish has more than 80% of the daily recommended intake.
There are approximately 48 micrograms of selenium in each serving of sardines.
A 4-ounce piece of beef can provide more than 40% of your daily intake of selenium.
A standard serving of chicken has more than 55% of your DV of selenium.
With about 50 micrograms of selenium in each serving, pork delivers about 77% of this mineral requirement each day. 
In one serving of cod, there is nearly 60% of your DV for selenium.
A single large egg provides about 15 micrograms of this mineral.
1 cup contains more than 15% of your daily intake of this mineral.
Other foods rich in selenium include the following:
There are roughly 10 micrograms of selenium in 100 grams of baked beans.
A 100-gram serving of whole-grain rye delivers about 50% of the selenium your body needs.
With 34 micrograms of selenium in 100 grams of these seeds, they are a nutrient-dense snack!
There are 8 micrograms in a 100-gram serving of lentils. 
3 ounces of this tasty fish is equivalent to more than 100% of your DV.
In 100 grams of sunflower seeds, there are 53 micrograms of selenium.
One serving of shrimp provides just over 100% of the daily required intake of this mineral.