The simplest way to picture a biodynamic farm might be as a closed loop. While many other farms rely on outside sources of energy, like fossil fuels or fertilizers (synthetic or natural), biodynamic farms strive to remain self-contained and self-sustaining. Energy sources—including compost, manure, medicinal herbal sprays (called preparations), or planned crop rotation—come from within the farm system itself, helping to increase soil fertility and reduce pests. Biodynamic farms also place a high value on water conservation and aim to preserve biodiversity by maintaining at least 10% of their land in the form of wetlands, grasslands, or forest.  More from Prevention: The Best Organic Packaged Foods Biodynamic farming has much in common with its organic cousin. Both prohibit the use of synthetic chemical fertilizers, pesticides, herbicides, and fungicides. But some experts believe the biodynamic method could have some additional benefits related to maintaining healthy soil. “There are some very small, preliminary studies showing that the herbal preparations used in biodynamic farming might help boost the microbial life in the soil. But it’s hard to claim that there’s one system that’s better than the other,” says Miller, who is also an associate clinical professor at the University of California, San Francisco. The exception: Biodynamic farms are far superior to very large, corporate organic farms, many of which have tossed true organic ordeals of sustainability by the wayside as organic food production has grown into a multi-billion dollar industry. “In some instances, big label organic uses practices that can be environmentally damaging, such as monocropping," says Miller. “They are essentially practicing unsustainable factory farming with organic inputs.” Still, even food grown on organic megafarms is a better choice than conventional, since the food remains free of toxic chemicals and genetically modified organisms. What’s preferable to both from an environmental perspective, though, is food grown on small-scale organic or biodynamic farms, which strive to preserve biodiversity employ truly sustainable practices. The best way to find it? “Know the farm and know the farmer,” says Miller. If the grower is certified biodynamic or advocates sustainable organic practices, chances are, they’re eager to let people know about it.  More from Prevention: Organic Fruits And Veggies Shopping Guide