I have no idea why that or any finish would not be food safe. Now if the food could somehow leach into the finish and chemically degrade it, then you have an issue. Of if you slice into the bowl and they eat an actual chip of the finish. Both are extremely unlikely. You should protect yourself when using shellac and DNA though. DNA now has a high percentage of methanol in it. Methanol has a sorted history in America, especially during prohibition. It's formula is to make it poisonous for human consumption. Absorption through the skin is also an issue, but not nearly as dangerous as drinking it.