The move from saturated fats (e.g. butter, beef tallow) to trans fats (e.g. margarine) was not necessarily a good one. Sometimes I wonder if most nutritional advice just follows constantly changing fads...
This study gets around this because the trans-fat ban (which took a long time to come because of the above factors) was a nationwide thing and so lack of access means we can make assumptions. Even then they had to figure out what was this ban, what was smoking becoming less common, and what was increased use of statins, which is statistics that depending on input assumptions.
1) Eat food. This is basically saying eat stuff that is traditionally considered food in different cultures (i.e., stuff that has been eaten for centuries) because doing nutritional studies is hard, but the fact that certain cultures have thrived for centuries and even millenia eating "food" provides decent evidence that it works.
2) Not too much. This is necessary as a restriction to #1 because in the past it wasn't easy or even possible to eat "too much" since you didn't have modern conveniences that make it easy to prepare food and you couldn't just order it for delivery. So you have to explicitly ensure you don't eat "too much", something that was implicitly enforced in the past.
3) Mostly Plants. If there is one thing all nutritional studies have found, and the one thing that pretty much all the science in this area can agree upon, is that eating plants (i.e. vegetables) is good for you, and for the most part, the more the better. But also note that he is saying "Plants" and not "Veggies" in a nod to the idea that it should be largely simply prepared and as close to its natural formation as possible, so buying a bag of "veggie straws" does not count.
Plenty of cultures heavily process their plants, and for good reason: the raw form is less nutritious. Plants != vegetables. Vegetables exclude fruits and uncultivated plants; wildflowers are delicious and definitively plants but debatably veggies [1].
Chocolate is an example of a food that is highly processed just for it to be reasonably less bitter and unpromising as it is in raw form.
Unfortunately, the need to get recommendations out on a political schedule meant that they went ahead of the available evidence. This Washington Post piece from 1977 debating the then-proposed guidelines includes an interesting quote:
> Dr. Mark Hegsted, professor of nutrition at Harvard University and one of the three nutritionists who helped write the report, said: "There will undoubtedly be many people who will say we have not proven our point; we have not demonstrated that the dietary modifications we recommend will yield the dividends expected.
> "The question to be asked therefore, is not why should we change our diet, but why not. "What are the risks associated with eating less meat, less fat, less saturated fat, less cholesterol, less sugar, less salt and more fruits, vegetables, unsaturated fat - and cereal products - especially whole-grain cereals? There are none that can be identified and important benefits can be expected."
That “but why not” line of reasoning is interesting given the mixed status of the recommendations in the next sentence. Eating more fruits, vegetables, whole-grains, etc. and less sugar is still widely accepted as good advice now but the remainder of the guidelines are problematic, particularly now that we have a better understanding of e.g. how fat interacts with satiation or how the food industry scrambled to produce alternate versions of familiar foods without key ingredients.
What we do know now is that millions of people had worse health outcomes due to that rush because even though studies came out only a few years later in the 80s rejecting the theories about salt, fat, specific foods like eggs, etc. the ghost of that Nixon-era rush job hung around until the 2010s and isn’t completely gone yet. You can still see a ton of food loaded with sugar because the recipe was modified decades ago to remove the fat & salt which made it taste good, not to mention how often people pass over vegetables because someone said it was unhealthy to butter or fry them without considering that this made the most likely outcome skipping them entirely.
[0]: https://www.eatthis.com/mcdonalds-french-fries-taste-differe... [1]: https://www.chicagotribune.com/news/ct-xpm-1990-07-24-900302...
https://theconversation.com/how-palm-oil-became-the-worlds-m...
Nutrition is not guided by fads, but by food manufacturer and retailer profit margins.
The reason for change is often forgotten or even misunderstood. From what I've read there is nothing wrong with eating saturated far or unsaturated fat, but transfat (a.k.a. partially hydrogenated) is very bad for you, as it chokes the machinery for "consuming" one or the other by being a bit of both.
After the crusade against fat, people also seemed to get the idea that eating fat makes you fat (the original reasoning had more to do with heart disease), but keto and low-carb diets that work would beg to differ. You gotta read the actual results to get to the bottom of things.
The body can deal with saturated and unsaturated fats. It has the enzymes to transport and handle them. They're a normal constituent of membranes.
Trans fats have no place in the body, and they do not arise naturally. You don't have the programming to deal with them. Their structure increases membrane rigidity, decreases lipid raft mobility, impairs cellular function.
Don't put trans fats into your body in any quantity.
But, from wikipedia:
> A type of trans fat occurs naturally in the milk and body fat of ruminants (such as cattle and sheep) at a level of 2–5% of total fat.
Not everything about traditional food is good. Cured meats, for example. But a too-convenient solution is often too convenient to be true.