They appear to block the production of fat cells, even when animals are fed a high fat diet:
The study also showed that in mice fed a high-fat diet, resveratrol improved resistance to weight gain. Also, supplementation with the combination of vitamin D and the phytochemicals resveratrol, quercetin and genistein in aged rats with their ovaries removed not only resulted in decreased weight gain, but also improved bone health.
I take 600 mg of resveratrol and 5000 U of vitamin D daily. I do not recommend you taking that dose of vitamin D without checking with your doctor and gettings blood levels measured.
Is Resveratrol ok to take?
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I share my experiences and medical literature, but I am not practicing medicine. I recommend seeing your own physician to make medical decisions.