Replacing animal fat with vegetable oil is associated with a lower risk of developing dementia in older adults. Based on a long-term analysis of dietary habits, researchers found that the specific types of fats a person consumes were correlated with later cognitive health. The study was published in The American Journal of Clinical Nutrition.
Dementia is a progressive neurological disease characterized by a decline in memory, thinking, and reasoning abilities. The global number of people with dementia is expected to rise sharply in the coming decades, making identifying ways to prevent or delay the onset of dementia a top public health priority. Currently, there is no cure for dementia, so medical professionals frequently turn to modifiable lifestyle factors to preserve cognitive function.
Diet is one of the most prominent of these factors, but the relationship between dietary fat intake and dementia remains unclear. Fat is an essential nutrient for the human body, especially the brain, which is largely composed of adipose tissue. Certain fats are needed to build cell membranes, remove harmful proteins, and manage inflammation. However, previous studies examining how fat intake affects the brain have yielded inconsistent results.
Many past analyzes either did not take into account total daily energy intake or failed to assess what happens when one type of dietary fat is replaced with another. This concept, known as the isocaloric substitution model, looks at the health effects of keeping a person’s total daily calories the same while swapping calorie sources. To better demonstrate how certain fats influence cognitive decline, the researchers launched a new observational study.
The study was led by Minyu Wu and Changzheng Yuan from Zhejiang University School of Medicine in China, along with collaborators from research institutions in the United States and Denmark. They wanted to determine whether replacing saturated fat with healthier alternatives could serve as a practical strategy for dementia prevention.
The researchers analyzed data from the Health and Retirement Study, a large, ongoing survey of older Americans. They identified 5,944 participants who did not have any dementia at the time dietary data was collected in 2013. At the beginning of the observation period, the average age of the participants was 68 years, and nearly 60 percent of the group was female.
To understand what participants ate, the researchers used a food frequency questionnaire that included 164 specific foods. This allowed the research team to calculate each person’s intake of different types of fat. Researchers classified dietary fats according to their source, separating animal and vegetable fats.
The food questionnaire asked participants to report how often they ate certain items throughout the year. This included everything from cooking oils and butter to certain types of meat, nuts, and dairy products. The researchers used established nutritional databases to convert these dietary reports into an estimated percentage of total daily fat intake.
They also classified fats by chemical structure. This includes saturated fats, which are usually solid at room temperature and are found in meat and dairy products. They also measured monounsaturated fats and polyunsaturated fats (liquid oils, usually from plants or fish). Finally, we discussed trans fats, which are synthetically processed oils often used in processed foods.
The researchers tracked the participants’ cognitive health over a median observation period of six years. They used a combination of self-reported diagnoses, memory tests, and interviews with proxy respondents such as family members. Cognitive tests assessed memory through a word recall task, as well as attention and calculation ability by having participants count backwards.
By the end of the follow-up period, 444 participants had developed dementia. Researchers looked only at total fat intake in the daily diet and found no association with dementia risk. However, when fat intake was broken down by source and type, distinct dietary patterns emerged.
Participants who ate the most vegetable fats had a 31 percent lower risk of developing dementia than those who ate the least. The median intake for this top tier was approximately 23.5 percent of total daily calories from vegetable fats. In contrast, total animal fat intake itself did not show a statistically significant relationship with dementia.
The benefits of vegetable fats became even more apparent when researchers ran statistical models that simulate dietary changes. It was found that replacing just 5 percent of a person’s total daily calories from animal fat with the same amount of vegetable fat reduced their risk of dementia by 15 percent. Replacing 5 percent of your daily calories from carbohydrates with vegetable fats also corresponds to a reduced risk.
When looking at the chemical makeup of fats, diets high in saturated fat were associated with negative outcomes. Participants in the top five saturated fat intakes had a 56 percent higher risk of dementia than those in the bottom five. Conversely, higher intakes of monounsaturated fats were inversely associated with poorer cognitive function. This means that the higher your intake of monounsaturated fats, the less likely you are to develop this condition.
Isocaloric substitution models strengthened these associations. Replacing 5% of your daily calories from saturated fat to monounsaturated fat reduces your risk of dementia by 48%. It was found that replacing the same amount of saturated fat with polyunsaturated fat reduced the risk by 33%.
Monounsaturated and polyunsaturated fats appear to be beneficial, but why are saturated fats harmful? Saturated fats can cause increased inflammation and problems with vascular function. The brain relies on a vast network of very small blood vessels to transport oxygen and nutrients. Damage or restriction of this vascular network can starve brain cells.
Unsaturated fats, on the other hand, are essential components of the structural membranes of neurons. Plant-based fats and oils contain high levels of these unsaturated fats, along with other beneficial plant compounds. These additional compounds act as antioxidants in the human body.
Antioxidants help protect brain cells from oxidative stress, a biological process in which unstable molecules damage structural fats in cells. A diet rich in vegetable oils may create a safer environment for neurons to grow as we age by providing both structural building blocks and protective antioxidants.
The researchers noted that the protective pattern for vegetable fats was particularly strong among people with no history of depression or who had never consumed alcohol. Conditions such as depression can inhibit the body’s ability to process fat and increase inflammation in the brain. This may negate the neurological benefits of plant food compounds, but the researchers noted that further research is needed to understand this link.
Results were consistent across different demographic groups. The protective association of vegetable fats remained independent of age, gender, race, and history of cardiovascular disease. Researchers also accounted for genetic factors by controlling specific genetic genetic markers associated with Alzheimer’s disease risk. Controlling for these genetic traits slightly reduced the estimated effect size, but maintained the overall trend in favor of plant-based fats.
Despite the large sample size and detailed tracking of diet, this study is observational and cannot prove that eating vegetable fats directly prevents dementia. Other unmeasured health behaviors and underlying metabolic conditions may explain some of the association. Although the researchers controlled for physical activity, income, and education level in their models, people who eat more plant-based diets may also get more exercise and receive better health care.
Additionally, dietary data relied on questionnaires that relied on participant memory. Recalling eating habits over a long period of time can lead to errors in reporting. To ensure that early stages of cognitive decline did not cause participants to make dietary changes that would skew the results, the researchers ran a test that excluded people diagnosed with dementia early in the study. This reduced some of the statistical strength, but the overall trend remained stable.
The study also treated all forms of dementia as a single outcome, rather than distinguishing between specific types such as Alzheimer’s disease or vascular dementia. Because vascular dementia is closely linked to cardiovascular health and saturated fat intake, the physiological effects of some types of cognitive decline may be stronger than others. The researchers noted that future studies are needed to confirm these dietary patterns in other populations and elucidate the exact biological mechanisms by which vegetable fats protect the brain.
The study, “Association between dietary fat intake and long-term risk of dementia: a prospective cohort study,” was authored by Minyu Wu, Liyan Huang, Yuhui Huang, Jie Shen, Hui Chen, Binghan Wang, Geng Zong, Marta Guasch-Ferre, Shuang Rong, Xiaoran Liu, and Changzheng Yuan.
