There’s been a lot of goodwill towards rice lately among the more open-minded bloggers in the Paleo community. Sure, it’s a Neolithic food, but there hasn’t been much of a case against occasionally consuming white rice for people with normal metabolic function. Removing the bran from rice (to create the white variety) removes the antinutrients too. So it may not be especially nutritious, but if you’re an athlete looking to retain or gain muscle mass, it’s a safe source of carbs.
Or so we thought.
A new study shows that very small pieces of rice RNA (microRNA) can enter the blood stream, then bind to recepters in the liver that normally work to reduce LDL cholesterol, resulting in an increase in plasma levels of LDL cholesterol.
OK calm down. Before demonizing rice we’ll want to understand whether it affects small, dense LDL or large, boyant LDL, and we’ll need someone who understands biochemistry to interpret the study to get a clearer picture of it’s significance. Maybe the effect is small or counteracted by other properties of the food. Who knows? Not me, this is way above my pay grade. But it’s pretty interesting none the less that bits of rice RNA can enter the bloodstream and alter human gene expression.
The authors also suggest that microRNA may be considered as a new class of bioactive chemicals in food like vitamins, minerals, or phytosterols. Fascinating.
Exogenous plant MIR168a specifically targets mammalian LDLRAP1: evidence of cross-kingdom regulation by microRNA.
Our previous studies have demonstrated that stable microRNAs (miRNAs) in mammalian serum and plasma are actively secreted from tissues and cells and can serve as a novel class of biomarkers for diseases, and act as signaling molecules in intercellular communication. Here, we report the surprising finding that exogenous plant miRNAs are present in the sera and tissues of various animals and that these exogenous plant miRNAs are primarily acquired orally, through food intake. MIR168a is abundant in rice and is one of the most highly enriched exogenous plant miRNAs in the sera of Chinese subjects. Functional studies in vitro and in vivo demonstrated that MIR168a could bind to the human/mouse low-density lipoprotein receptor adapter protein 1 (LDLRAP1) mRNA, inhibit LDLRAP1 expression in liver, and consequently decrease LDL removal from mouse plasma. These findings demonstrate that exogenous plant miRNAs in food can regulate the expression of target genes in mammals.
1. Zhang L, Hou D, Chen X, Li D, Zhu L, Zhang Y, Li J, Bian Z, Liang X, Cai X, Yin Y, Wang C, Zhang T, Zhu D, Zhang D, Xu J, Chen Q, Ba Y, Liu J, Wang Q, Chen J, Wang J, Wang M, Zhang Q, Zhang J, Zen K, Zhang CY. Exogenous plant MIR168a specifically targets mammalian LDLRAP1: evidence of cross-kingdom regulation by microRNA. Cell Res. 2011 Sep 20. doi: 10.1038/cr.2011.158. [Epub ahead of print] PubMed PMID: 21931358.