> Since the mechanism by which TFA increases CVD risk is separate to this, this is compatible with TFAs causing harm.

As far as I know, the main mechanism for that is reduction of HDL-c. However, the study you cite found no reduction of HDL-C from TFA substitution.

> PUFA reduces LDL-c by a greater degree and there are no known issues like there are with TFA, so substituting SFA for PUFA seems like a no-brainer.

Key word being "known issues". One of the major issues with nutrition science is this grouping of vastly different foods based on a single simple category of substance. There are a lot of different PUFAs, and even more different specific oils or fat solids containing PUFAs, and there is no reason to believe that they are completely interchangeable in our nutrition. UFAs were once thought to be the same, before the important distinction between PUFAs and TFAs (and the still unclear position of non-TFA MUFAs) was discovered and recognized.

> As for nutrition science and its effect on health, just because one intervention had deleterious effects doesn’t mean that you can claim that the net effect of nutrition science on health has been net negative. Again, see no reason to believe that without actual evidence supporting it.

Yes, some basic findings in nutrition science did improve things worldwide health. The discovery of vitamins and various other micronutrients was by far the most important. The discovery of dietary fiber and its roles allowed nutrition science to course correct a number of bad recommendations from the earlier era. In very specialized fields, such as high performance athletes, it also show reproducible, predictable results (though not necessarily on long-term health, just measured by competition success).

> I see no reason to believe that traditional foods are safer than novel foods. In fact, provided both are equally health promoting during the reproductive window, then it’s more likely that a given novel food is better for longevity than a traditional one.

Traditional foods have an extremely long history behind them of not being acutely harmful to at least one particular population, with traditionally passed on limits of safe amounts of consumption and safe methods of preparation. They have been consumed by populations that lived with much reduced medical care than today, so they are known to be resilient even in the absence of medical interventions, which often confound nutritional studies, especially in older adults. They are also much more likely to be well adapted to the particular genetics of a certain population, unlike nutritional advice which is almost entirely "universal".

One of the main sources of nutritional discoveries has in fact been the study of traditional diets. From vitamins to fiber to fermented foods' effects on gut microbiota, the discovery has always come from trying to understand why a particular population is thriving nutritionally.

The main drawback of traditional foods is that the mechanism for passing down information on safe preparation and consumption was informal, and can be easily lost. They also tend to be hard to create industrially, so they are likely to be much harder or more expensive to consume compared to modern industrial food products. However, for people who can afford it, they are by far the better option compared to the uncertainty and contradictions of modern nutritional advice.

[Note: this is the same account as tsimiones, I'm not trying to hide behind some new name, it's just related to some software on my work PC]

There have now been several intervention trials investigating whether HDL-raising meds improve health outcomes (there’s no evidence to show they do) and MRs looking at genetically determined HDL-c and various health measures (no evidence of effect either). We don’t actually have any evidence that HDL is anything other than a proxy for other factors, and no evidence that it directly affects anything.

Yes, there are no known issues. You can speculate that there might be, but we could equally speculate that they’re actually superfoods and we don’t know it yet. At the end of the day, speculation is all it is so I believe it’s most sensible to apply the principle of indifference and look only at what we do know. That is, margarine is a sensible replacement for butter on the current evidence.

Because of antagonistic pleiotropy, we can actually make an a priori argument that given two foods that are equally health promoting within the reproductive window (I.e. it’s not killing or neutering people before the age of ~50), then probability holds that the food to which we are least adapted is actually more likely to promote longevity than the ancestral food.

Because adaptations are on net more likely to be antagonistically pleiotropic than not, foods to which we are most adapted are more likely than not making a trade off in favour of reproductive success over longevity. Since we don’t have these adaptations to novel foods, this concern does not apply to them.

Therefore, given butter and margarine are both similar in their effects on reproductive success, with no further information at all we should favour margarine. The fact there are studies confirming this is just icing on the cake.

You're making very strong claims based around broad trends in genetics for a process that isn't entirely genetic. The society that is choosing what to eat and how to prepare it is doing so based on their own set of axioms, not pure genetic biology.

The argument is probabilistic, it’s not required that food seeking behaviours are entirely genetic for it to go through. As long as food seeking behaviours and/or preferences are to some degree genetically determined, then the argument is sound and valid.

If I can safely discount all human behavior through history, then I can also assume that the behavioral changes you are espousing are equally non-relevant. Either human behavior can be a greater driver than genetic probability or it can't.