No, it's not true that the breast tissue caused by gynecomastia can never go away. According to the Mayo Clinic (emphasis mine):
Most cases of gynecomastia regress over time without treatment.
However, if gynecomastia is caused by an underlying condition, such as
hypogonadism, malnutrition or cirrhosis, that condition may need
treatment. If you're ...
The following comprehensive scientific sources do not even mention any relationship between turmeric/curcumin and gynecomastia:
Turmeric, Natural Medicines Comprehensive Database, komen.org
Turmeric, National Center for Complementary and Integrative Health
Curcumin: A Review of Its’ Effects on Human Health, PubMed, 2017
Curcumin, Examine.com, 2015
A double-blind crossover study of placebo and the antiestrogen tamoxifen in ten men with gynecomastia of diverse etiology showed that:
The reduction of breast size was partial and may indicate the need for a longer course of therapy. A follow-up examination was performed in eight out of ten patients nine months to one year after discontinuing placebo and ...
There seems to be no clear and direct evidence for this.
But a few angles might be worth exploring:
Molecular Dynamics (MD) simulations found curcumin to be a stable inhibitor of aromatase (Singh et al 2016).
The prepubertal gynecomastia in males and breast hypertrophy in females are conditions of aromatase excess syndrome (Metwalley and Farghaly 2013).
According to this review article:
Estradiol and, to lesser degree, other estrogens, increase proliferation of breast epithelium and stroma and, consequently, increase the chances of mutation in rapidly proliferating epithelium
Tamoxifen and other SERMs generally act as competitive antagonist on breast estrogen receptor, which decreases estrogen's ability ...
First, vitamin D supplementation does not seem to increase testosterone levels. Most high quality trials see either no increase, or a very very small one:
Second, zinc might negate a transient exercise-induced decrease in testosterone. There is no evidence this is clinically meaningful: