What is the dietary drawback mentioned regarding the tannins in green tea?

They can inhibit non-heme (plant-based) iron absorption

While green tea is celebrated for its powerful catechins, especially EGCG, which aid in boosting metabolism and fat oxidation, a specific caution must be observed regarding its consumption timing relative to iron intake. The tannins naturally present in green tea possess the property of binding with non-heme iron, which is the type of iron derived exclusively from plant sources. This binding action effectively blocks or inhibits the digestive system's ability to absorb this vital mineral. To ensure adequate iron status, particularly for those relying on plant sources, it is recommended to allow for a waiting period of roughly one hour following an iron-rich meal before drinking green tea.