Final answer:
Porphyry, an edible red alga, is a good plant-based source of iodine and potentially vitamin B12 for vegetarians or vegans. Marine vegetables are, in general, rich in iodine. However, some foods contain substances that can inhibit iodine absorption.
Step-by-step explanation:
When it comes to plant food that is a good source of iodine and vitamin B12, one should consider Porphyry, an edible red alga. This plant food is particularly beneficial for those following a vegetarian or vegan diet since vitamin B12 is typically obtained from animal sources. Porphyra is believed to contain vitamin B12, although it is important to note that some reports suggest that the vitamin B12 analogs it contains may not fulfill all the necessary functions in the human body.
As for iodine, marine vegetables are rich sources due to their ability to concentrate iodine from seawater. However, people living in regions far from the sea or at high altitudes may not get enough iodine from local vegetation because of lower concentrations in soil and water. In such cases, iodine is often added to table salt to prevent deficiencies.
Remember that certain foods like cabbage, cauliflower, and radish contain goitrogenic substances that can interfere with the availability of iodine in food. Therefore, they may not be reliable sources of iodine despite containing it in natural forms.