I haven’t seen any studies suggesting that phytoestrogens increase your endogenous estrogen levels. But they are estrogenic by definition, and can thus increase estrogenic activity in your body. The problem with food-related studies is that most of them are observational in nature. So instead of placebo-controlled double-blind studies, most food studies rely on observation and food intake questionnaires to draw a correlation (which is different from causation). What makes the situation even worse is the influence of food manufacturers on these studies. As a result, it’s almost impossible to find well-designed research on the impact of soy among the dozens of studies that were sponsored by the food industry. My take on phytoestrogens is simple: there’s nothing in plants that have phytoestrogens that is essential to my health. So I avoid them, and I suggest you do too.