Since I started taking 600mg a day of trans-resveratrol, my bowel movements have become reliably punctual, sometimes almost overly so. If you are taking large doses of resveratrol and are experiencing the same phenomenon or worse, it may be due to emodin, an impurity commonly found in commercial resveratrol supplements. Among other properties, it is a laxative. Emodin is a phyto plant substance present in rhubarb and in aloe vera leaves. Emodin is also present in Japanese knotweed (Polygonum cuspidatum), the source ingredient of most resveratrol supplements. It may not all be removed in refining resveratrol and can represent more than 5% of the content of a marketed resveratrol supplement capsule. Discussion of this impurity has appeared in an Imminst.org forum on resveratrol.
The amount of the impurity varies significantly by product. Most popular suppliers of resveratrol (including Swanson Vitamins, NSI, Country Life, Biotivia, Life Extension InstituteJarrow Formulas, source Naturals and Puritan’s Pride) do not disclose emodin content in their resveratrol labels. Revgenetics is an exception and has posted laboratory analyses showing emodin is .1% present in their “99% pure” resveratrol product(ref) and .7% present in their “50% pure” product(ref). Some grape-based resveratrol products avoid emodin completely(ref).
Despite its laxative effects, emodin may offer health benefits of its own such as a cancer-preventative ones. It may inhibit cell growth and angiogenesis in human colon cancers(ref), It “could be a useful chemotherapeutical agent for treatment of hepatocellular carcinoma(ref),” “Emodin affects the expression of genes involved in various cellular functions and plays important roles in cell apoptosis, tumor metastasis and chemotherapy-resistance, which suggests emodin might become an effective chemopreventive or chemotherapeutic agent for small cell lung cancer(ref),” “Emodin induces apoptosis in human promyeloleukemic HL-60 cells—(ref).” Further, Emodin has unique antibacterial properties, “taking into account its unique cytotoxicity profile and mode of action, aloe-emodin might represent a conceptually new lead antitumor drug(ref).” And emodin is “a potential lead compound for further anti-bacterial drug discovery(ref).” To sum it up, emodin appears to be another phyochemical whose possibly important health properties are just-now being systematically explored.
Personally I am taking a resveratrol supplement with less than 1% emodin content and find the laxative effect definitely present but tolerable. If you are experiencing diarrhea due to taking a large amounts of resveratrol, you might want to switch to a different brand with lower emodin content.