I wonder if this is because it has less to do with fat and carbs and more to do with processed foods.
The Mediterranean diet is regarded as quite healthy by many health professionals but, it is also high in carbs and fat. But these are healthy, unprocessed carbs and fats. Whole grains and olive oil.
People going for high fat, low carb / low fat, high carb are usually doing so while also sticking to real foods.
Cochrane systematic reviews should make you seriously question whether the Mediterranean diet really is much good at all - hard data is inconclusive and low quality [1].
In general we really even barely have enough nutritional knowledge to say if the term 'good fats' even makes much scientific sense, but broad and vague things like "Mediterranean diet" are just total nonsense, from the standpoint of serious nutrition science.
That seems to be searching for RCT's, which, I'm not surprised would struggle to replicate. Most of these had a duration of less than 5 years, while dietary related health outcomes are the result of decades of following a pattern. It's possibly also unethical, in some cases (i.e. the existence of effective LDL lowering medication would likely complicate things).
Many people seem to disregard epidemiology, especially when it comes to nutrition (I think because it tends to support unpopular positions). But epidemiology has performed some excellent feats in the name of public health: cholera, smoking, pfao.
It is unfortunate that the large time-lines on these things make more rigor difficult, but I wouldn't throw out the epidemiology.
Epidemiology should generally be disregarded when it comes to nutrition.
There are exceptions when there are rare natural experiments (e.g. I forget the country, but the European one where some issue caused all flour for the country to be only whole-wheat, which led to clear nutrient deficiencies due to the phytic acid there) but in general there are way too many confounds, and measurement is far too poor and unreliable (self-report that is not just quantitatively but qualitatively wrong, and you can't track enough people nearly long enough), there is virtually no control whatsoever (diets and available foods shift considerably over just decades), and much of the things being measured lack even face/content validity in the first place (e.g. "fat" is not a valid taxon, and even "saturated vs. unsaturated" is a matter of degree).
We are missing so much of the basics of what are required for a real science here I think it is far more reasonable to view almost all long-term nutritional claims as pseudoscience, unless the effect is clear and massive (e.g. consumption of large amounts of alcohol, or extremely unique / restrictive diets that have strong effects), or so extremely general that it catches a sort of primary factor (too much calories is generally harmful, regardless of the source of those calories).
But even setting that aside, you can't define or study "Mediterranean diet" rigorously even in RCTs, so I don't see how you can think you are going to get much of anything here from epidemiological work that is going to lead to anything practically actionable.
No, they are not. Dietary cholesterol has little to zero impact on blood cholesterol, and saturated fat we don't have reliable data that points to it being harmful either, when accounting for other influences.
> Dietary cholesterol has little to zero impact on blood cholesterol
The "well, actually" point on this is that dietary saturated fat drives blood cholesterol levels more strongly than dietary cholesterol. But it is not true that dietary cholesterol has "zero impact," and it is not true that "saturated fat we don't have reliable data that points to it being harmful." High-cholesterol foods are typically high in saturated fat, so these things are kind of intertwined.
Yes. Sugar (and all of its downstream phenomena - diabetes, insulin resistance, the ease in which sugar adds calories without satiation signals) is well established to contribute to CVD. Long-chain (animal based) sat fat and trans fat is also well established to contribute to CVD. The high calorie density of fatty foods plays a big role, as does the overall palatability and "eatability" of low fiber, high fat, high sugar, delicious foods, making portion control challenging. That should be uncontroversial at this point.
The jury is unclear on:
- How the chain length of sat fats impact things (medium-chain triglycerides seem to be protective, but the boundary between medium and long is fuzzy)
- How the ratio of the various omega-N (3/6/9) unsat fats impacts health, particularly inflammation
- The whole "seed oil" thing is probably MAHA/conspiracy style false signal at the end of the day, but it hasn't been fully debunked and there are almost certainly facets of truth to it (seed oils are a form of ultra-processed food, and all UPFs are problematic)
Confounders, confounders everywhere. This whole field is just extremely challenging and noisy.
There are many people with type 2 diabetes that are not overweight; and also many people with overweight and even obesity who do not develop type 2 diabetes. The estimate is that around 537 million people have diabetes worldwide, while overweight and obesity is estimated to affect 1.1 billion people.
Carbohydrates do cause insulin resistance and diabetes. India has average BMI of 21,9, yet has very high incidence of diabetes - largely thanks to its carbohydrate-based diet.