Saturated fat is perhaps the most demonized part of the American diet. Researchers and health writers routinely (and wrongly) blame heart disease on saturated fat consumption, and last week researchers writing in Annals of Neurology suggested that saturated fat may also be bad for our brains as we age.
The study was widely reported on Monday, but there are several important reasons to doubt that saturated fat has anything to do with cognitive decline. Indeed, there is some evidence that diets high in saturated fat are actually good for the brain.
As always, it's important to point out that this study isn't anything more than an observation and some complicated statistical analysis. The researchers studied the fatty acid intake of 6,183 older participants (ages 65 and over) from the Women's Health Study and found that participants who consumed more saturated fat performed worse on a series of cognitive function tests. But there's no way to establish a causal relationship between the two. And even if there was, the researchers only had data for elderly women, so there's no reason to think that the association between saturated fat and cognitive function holds for the rest of the population.
But here's something more important to consider. The link between saturated fat and heart disease doesn't exist; people who go on diets high in saturated fat lose weight; and humans and our ancestors have been eating animal fat for millions of years. Our bodies have no problem utilizing fat for energy, and even prefer it as an energy source. Given these facts, it would be rather strange to find that saturated fat hastens cognitive decline. Why would the body prefer an energy source that harms the brain?
Answer: it doesn't.
Multiple studies have shown that high fat diets can be used to treat and prevent varying degrees of brain damage. A 2012 study in which older adults were put on either a low or high carbohydrate diet (the former is typically high in saturated fat) for six weeks found that "... very low carbohydrate consumption, even in the short term, can improve memory function in older adults with increased risk for Alzheimer's disease."
Similarly, a 2006 review published in Behavioral Pharmacology found that ketogenic (high fat, low carb) diets offer effective treatment for Epilepsy, Alzheimer's disease, and Parkinson's disease. Researchers also found that ketogenic diets may protect against traumatic brain injury and stroke. The reason why the diet confers these benefits isn't fully known, but the authors suggest "... that neuroprotection results from enhanced neuronal energy reserves, which improve the ability of neurons to resist metabolic challenges, and possibly through other actions including antioxidant and anti-inflammatory effects."
Other studies have also found that low fat diets could actually be harmful to human health in a variety of ways. A 1996 paper published in the Journal of Nutrition, for example, claimed that a certain amount of dietary fat is necessary for children because it "... facilitate[s] maturation of the central nervous system, including visual development and intelligence." And a 2010 BMC Public Health study of an elderly Chinese population concluded that low intake of animal fat is associated with mild cognitive impairment. Like the study in question, this one was observational and the relationship the study's author's found may not hold for other populations. With the above information about the importance of dietary fat in mind, however, the association is on much firmer ground.
Unfortunately, the advice to eat less saturated fat probably isn't going away anytime soon. Like the baseless ideas that calories are calories or fat people simply lack willpower, fear of dietary fat has become entrenched in our thinking about nutrition, and won't die no matter how many times it's debunked. But if we're going to be lead to believe that saturated fat is harmful to our brains, the link should be based on more than observational research. I'm certainly not convinced that I need to eat less bacon, anyway.