Chances are if something is bad for the heart, it’s bad for the brain too. According to a recent study published in the journal Neuropsychopharmacology, a diet high in saturated fat can lead to cognitive function impairment, specifically by dulling the dopamine reward system while increasing the dependency on unhealthy foods.
The consumption of saturated fat and trans fat can raise low-density lipoprotein (LDL, or "bad" cholesterol) since the body naturally produces it. This is considered bad cholesterol because it contributes to plaque that can clog the arteries and make them less flexible, according to the American Heart Association.
Limiting the amount of saturated fats you eat to less than seven percent of your totally daily calories is recommended to keep LDL cholesterol at bay. For example, if you need about 2,000 calories a day (cal/day), less than 140 calories should come from saturated fats. Meanwhile, if you limit trans fats to less than one percent of your total daily calories (assuming that's 2,000 cal/day), less than 20 should come from trans fat. Eating fats that are monounsaturated or polyunsaturated are ideal for good health.
It’s no surprise that what we eat has a profound impact on brain function, according to a team of researchers at the University of Montreal. "Our research shows that independent of weight gain and obesity, high-fat feeding can cause impairments in the functioning of the brain circuitry profoundly implicated in mood disorders, drug addiction, and overeating — several states and pathologies that impinge on motivation and hedonia," said Stephanie Fulton, a professor at the University of Montreal's Department of Nutrition in the press release.
In an effort to show the effects of unrestrained intake of saturated fats on the brain, Fulton and her colleagues worked with three groups of rats. The first group of rats, or the control group, were given a low-fat diet containing equal amounts of monounsaturated and saturated fatty acids. The second group was given a monounsaturated high-fat diet where 50 percent of the calories were from fat derived from oil. Lastly, the third group was given a saturated high-fat diet where 50 percent of the calories were from fat, but they were derived from palm oil.
The high-fat diets were all the same in regard to sugars, proteins, fat content, and caloric density, and fat intake was unrestricted. After eight weeks, all of the rats still had comparable body weights and levels of insulin, leptin — major metabolic hormones — and relative glycaemia. The groups were tasked to undergo a series of behavioral and biochemical tests that are indicative of the functioning of rats’ dopamine systems.
The findings revealed that the rats on the palm diet showed significantly dulled dopamine function. The researchers hypothesize this is what leads the brain to try to compensate by heightening reward-seeking behavior, similar to how a drug addict increases their drug dose over time to get the same high. In this case, someone who is consuming too much saturated fat may compensate by consuming more high-fat and high-sugar foods to get the same level of pleasure and reward.
"As we were able to control for changes in body weight, hormones, and glucose levels, we think that the fats may be affecting the dopamine system by a direct action in the brain," Fulton said. "We in fact have separate evidence that brain inflammation could be involved in this process, as it is evoked by saturated high-fat feeding, which will be presented in a future publication."
A similar 2012 study published in the journal Annals of Neurology found bad fats can undermine all kinds of cognitive function, including short- and long-term memory as you age. Women who consumed the highest amounts of saturated fat, had worse overall cognitive function and memory throughout four years of testing when compared to women who ate the lowest amounts of these fats. Contrastingly, women who consumed the most monounsaturated fats fared better on the cognitive tests over time.
Although the study did not look at why bad fat might impair cognitive function with age, it’s been theorized that bad fats might be linked to inflammation or changes in lipid profiles. However, the researchers believe what connects saturated fat consumption with brain function requires further study. It makes sense that the same factors that are good for heart health are also good for cognitive function since good heart health has been linked to good brain health.
Limiting the intake of high saturated fat foods can prevent the impairment of cognitive function and the dulling of the brain’s pleasure center. Eating a diet rich in whole nutrient-dense, high-fiber natural foods can help restore dopamine sensitivity. Overeating to compensate can cause the brain to down-regulate receptors and lead to less enjoyment from other activities.
In the U.S., low saturated-fat intake has increased from 25 percent to 41 percent between 1976-1980 and 1988-1994, but there was no significant change from 1988-1994 through 2007-2010, according to the Centers for Disease Control and Prevention.
In the end, you are what you eat, but are you feeding your future health?
Sources: Fulton S et al. Dampened mesolimbic dopamine function and signaling by saturated but not monounsaturated dietary lipids. Neuropsychopharmacology. 2015.
Buring JE, Cook NR, Grodstein F et al. Dietary fat types and 4-year cognitive change in community-dwelling older women. Annals of Neurology. 2012.