It seems as if it was just yesterday when saturated fats finally recovered from their notorious reputation of being Satan’s heart clogging tool with two big studies which indicated no connection between saturated fat intake and an increased risk for heart disease. However, evidence has indicated a certain link, forgotten by the majority of people.
As always in nutritional science, physical health claims the forefront when talking about the healthiness of particular foods. But that’s a very simple and reductionist view. A recent review of multiple studies has assessed an important and perhaps missed link – the connection between saturated and trans fats and dementia.
Dementia is a devastating condition. The prevalence of dementia is on the rise in countries with an aging population. Alzheimer’s disease, probably the most known type of dementia, affected around 5 million Americans who are older than 65 in 2010. But that is not all, almost every projection indicates these numbers will go up in the following decades.
According to Herbert et al., by 2050 we can expect more than 13.8 million Americans who will suffer from Alzheimer’s. That number is enormous, especially when we account for its costs. Moreover, its impact on the social level is even more destructive. In dementias, whole families are usually affected because loss of memory has drastic consequences for everyone involved.
These increasing numbers are staggering. In the past few years, USA and a multitude of countries from Europe have started two initiatives to gain more knowledge about the brain. These should eventually lead to successful treatment options for dementias as well.
There are a lot of possible interventions which help reduce your risk of developing dementia. I’ve written about many of them before. They include increasing amounts of coffee, chocolate with high contents of cacao, consumption of omega-3 fatty acids, and green tea consumption.
Another lifestyle change called caloric restriction, and its cousin intermittent fasting, both seem to decrease your risk of developing Alzheimer’s disease too. The basic gist of either caloric restriction or intermittent fasting is lowering the amount of calories we take in. In caloric restriction, there is no particularly specific rule set on how to meet this reduction. However, intermittent fasting can be followed through various protocols, as I explained in the post I’ve linked above.
Moreover, adding coconut oil to diets of people who already have Alzheimer’s seems to benefit them because of the type of fatty acids found in coconut oil. Medium-chain triglycerides, or MCTs for short, give the brain with energy via a different metabolic pathway. [2, 3, 4]
In the past decade, different studies have assesd whether saturated fat is connected with an increased risk of developing either dementia or mild cognitive impairment, a preliminary condition foreshadowing Alzheimer’s disease, according to some researchers. The results from these studies seem to have been mixed. I will explain everything further down the article.
Some note an existing association between saturated fat intake and an increased risk of developing dementia, and particularly Alzheimer’s disease [5, 6, 7], as well as mild cognitive impairment. [8, 9]
Let’s take a closer look at these studies. The ones, which were assessing the connection between dementia and saturated and/or trans fat intake, noted a trend where increases in trans and saturated fat consumption also meant an increase in the risk of developing Alzheimer’s disease.
However, these associations were statistically significant only on a few occasions. This can mean either two things:
- The observed connection could have happened by chance
- The increase is actually connected to an increased risk of developing Alzheimer’s to a certain degree, but it doesn’t reach statistical significance
This is a really important issue. Therefore, it cannot be stressed enough – the mentioned studies represent correlational data. We cannot infer causal relationships from that. Saying “Saturated fat intake increases risk for dementia” is not practical, even if the correlations would be enormous. There is always a possibility of a third (or even more) confounding variable which might have affected these results.
In this particular case, it’s highly likely the people who have more saturated fat in their diet also have worse diets, on average.
A very possible, yet subjective, interpretation could be that people, who are around 60 years old and are health conscious, are probably still avoiding saturated and trans fats. Namely, when they were younger, state institutions started promoting the high-carb and low-fat diet, possibly affecting their dietary choices throughout their lifespan. The people who did not follow these rules (which were thought to be healthy at the time) stayed with their usual diet, characterized by high saturated and trans fat intake. It’s also very likely a good part of these people follow the typical Western diet and not a modern, health conscious high-fat diet like the paleo. However, this is only my interpretation, there are countless more possible ones.
Some of the before mentioned studies, together with some other ones, were also interested in the connection between saturated fat intake and mild cognitive impairment. Not to dive too deep, but as the name states, mild cognitive impairment reflects mild shortcomings in cognitive functioning. It can more often be found in the elderly population.
Again, in certain studies there was a significant association between the two, where in others, there was none.
If I summarize, with the available evidence, saturated fat intake is connected:
- To an increased risk of developing Alzheimer’s disease in three studies. A fourth suggests exactly the opposite connection.
- To an increased risk of dementia in one out of two studies.
- To an increased risk of mild cognitive impairment in one out of four studies.
- To an increased risk for cognitive decline in 2 out of four studies.
- In the two studies which assessed particularly for trans fats, no significant results arose.
All of the mentioned studies used food frequency questionnaires, this makes the results somewhat questionable by itself. Furthermore, again, they are only connections. A few well-placed randomized controlled trials, or intervention trials at least, would be required to assess the exact nature of this relationship and whether there is actually something behind this observed connection.
The amount of saturated fat did vary substantially between the studies. The lowest amount was from 5 grams of saturated fat per day even up to 35 grams of saturated fats. This has obvious implications for the interpretability and importance of these results. It would be interesting to see the results if there would be a similar amount of saturated fat across studies.
Another important implication is the ApoE status of participants. ApoE is a type of apolipoprotein which is essential for the normal catabolism of lipoproteins rich with triglycerides. Furthermore, it mediates cholesterol metabolism.
However, it plays the role of a transporter for cholesterol in our central nervous system, as it transports cholesterol to neurons via apoE receptors.
You might be wondering why I’ve suddenly started talking about this. Well, it turns out, its gene with the same name, or at least one of its variations, is the largest known genetic risk factor for Alzheimer’s disease in a lot of different ethnic groups. For example, Caucasian people who carry 2 copies of this variant (E4) are 10 to 30 times more likely to develop Alzheimer’s disease by the age of 75. 
Not a small number by any means.
With all that said, no firm and definitive conclusion can be drawn from this. It’s possible all the noted connections were due to generally bad dietary choices of people who had a high saturated fat intake. However, having found this connection, further studies will be a welcome addition.