That wasn't the example I gave. The issue is living exclusively off peanut butter and white bread. Specifically it is the lack of dietary variety to get a prope

That wasn't the example I gave. The issue is living exclusively off peanut butter and white bread. Specifically it is the lack of dietary variety to get a proper mix of various nutrients which is the issue. There are lots of things out there that will give you about 80% of what you need, the issue is that all the cheap options are giving you roughly the same 80%, consistently and completely filling in that gap is hard. For example iodine is critical for regulating metabolism, but most foods which contain significant amounts (like seafood) are expensive, and cheaper sources (like eggs) need to be consumed in large amounts, offsetting their low expense, and causing other issues balancing diet. If you have an iodine deficiency you don't die, but with your metabolism out of whack it is again harder to maintain your health. Now if you go to your doctor they might be able to identify an iodine deficiency and get you supplements or have you buy specialty products like iodized salt, but this reduces to the more general problem that healthcare in the US is incredibly messed up and disproportionately difficult for those in poverty to access reliably. 92% of the US population has some vitamin or nutrient deficiency. Basically, mistaking the malnutrition issue as just people not having access to a good cookbook is exactly the problem.