Okay. But I am someone who isn't terribly fond of rubbing petroleum based laxatives on my knives and cutting boards. And I've had good results with walnut oil, so I mentioned it as another option for those that might be interested. Those that aren't interested don't need to worry about it. Right? This isn't personal. This is walnut oil.
I'm not even sure how much it matters where knives are concerned. I will offer this though: it does matter in the kitchen on cutting boards. Mineral oil doesn't harden. It stays in a gloopy, pliable film. As you slice into the film on cutting boards, you allow bacteria to get under the film. This is not the case with oils that harden or polymerize or whatever.
I get it, not at all contentious. My point is that it has already been proven by the FDA through clinical trials and decades of use that the occasional ingestion of USP mineral oil at the prescribed dosage has no adverse health effects on humans at the dose of 1 to 3 tablespoons (15 to 45 ml). My point is that the amount of mineral oil transferred from a knife and hands to the food during food preparation is probably tens of thousands (or more) times less than the recommended dosage as a laxative. At the above dosage, reported side effects include: Rectal seepage, anal irritation, pruritus ani, rectal reflex impairment, infection/impaired healing of anorectal lesions. Not something I would want (man I am glad we do not have the smell-o-vision app for this discussion). I am confident in saying that the trace amounts of USP mineral oil transferred to foods from knives during food preparation will have no ill effects.
Your point regarding mineral oil use on cutting boards is well taken. Since this oil is completely saturated, it is resistant to oxidative degradation and will remain unchanged at room temperature environments for a long period of time. I think this is why many makers of cutting board treatments put paraffin wax into their mixtures. The oil is absorbed into the wood via capillary action, and the wax forms a seal on the surface. Mineral oil only treated boards will be more prone to being cut deeper, and hence introduce bacteria into the cuts. But this is true regardless of the cutting board material. Care and hygiene are definitely called for. Dedicated raw meat boards and cooked meat boards should be implemented as well as vegetable boards, if you are that concerned about bacterial contamination. But again, bacterial infections are a numbers game with the human body, and cooking kills bacteria. What you want to avoid is contaminating something that you are going to put a lot of bacterial growth media into (mayonnaise, salad dressing) and then store for an extended period (potato/pasta salad).
Linoleic and Linolenic acids are unsaturated fatty acids, and they can go rancid as described above. However, I am not aware of any adverse effects of ingesting rancid oil. My understanding is that they just stink. The seasoning of a cast iron pan is a different animal altogether. That process is referred to as carbonization. The carbon in oils, proteins, starches and other organic compounds is heated to give off CO2 and other gasses and a film of essentially elemental carbon forms on the surface of the iron, hence protecting it from rust.
I do get it that you do not want to ingest a petroleum product. And for those like minded individuals, your walnut oil suggestions appear to provide a good alternative. But the science says that occasionally ingesting USP mineral oil at much larger doses than the trace amounts on a knife is safe, so I would turn the table and ask that you to prove that ingesting trace amounts from a knife blade or handle is not safe. The only scientific data that I am aware of indicates that it is safe. If you have data indicating otherwise, I am certainly open to it, and would even change my position, assuming that the study was performed properly.
