The myth that saturated fats and cholesterol are inherently unhealthful is just that… a myth. For more on that, see “Cholesterol Fiasco Undermines Accepted Theory.”
But this doesn't mean there's no downside to diets that are too high in saturated fats from meats and dairy, and too low in unsaturated fats from plant foods.
For example, see “Dietary Fat May Affect Kids' Memories” and “Beef-Dairy Fat May Fool Brain's Appetite Signals.”
And epidemiological studies from Europe associate such diets with greater risk of “mild cognitive impairment” (Solfrizzi V et al. 2010).
Now, a study from the Mayo Clinic seems to ratify the earlier European results.
Before we examine that research, it'll help to clarify the nature of the brain condition and the unsaturated fats in question.
Study examines two kinds of unsaturated fat in brain decline
The Mayo clinic study looked at the instance of “mild cognitive impairment: or MCI, which is a common condition midway between normal, symptom-free brain aging and dementia.
People with MCI can function reasonably well in everyday activities, but may have difficulty remembering details of recent conversations, events and upcoming appointments, or in planning and making decisions.
Most but not all patients with MCI develop a progressive decline in their thinking abilities over time.
Alzheimer's disease is usually the underlying, undiagnosed cause of MCI, but some patients may progress to other, rarer types of dementia.
We should explain that there are two kinds of unsaturated fat:
Monounsaturated fats predominate in olive oil, macadamia nut oil, and canola oil.
Polyunsaturated fats abound in nuts, seeds, and seed oils (omega-6s) and fish (omega-3s).
Leafy greens, walnuts, and flaxseed also contain omega-3s, but they are a short-chain variety called ALA.
While omega-3 ALA is beneficial, the body must convert it, very inefficiently, into the long-chain omega-3s (EPA and DHA) actually needs for basic metabolic, immune, eye, and brain functions.
U.S. study links saturated fat to brain decline
The results come from research performed as part of the Mayo Clinic Study of Aging.
The investigation involved volunteers from Olmsted County, Minnesota, who were 70 to 89 years old at the start of the study in October of 2004.
The 1,233 participants from this pool completed a 128-item food frequency questionnaire and reported their food intake within the last year.
According to lead author Dr. Rosebud Roberts, they were asked about the fats used in cooking, bread and potatoes, and their milk fat preference, in addition to other dietary sources of fats.
A panel of nurses, physicians, and neuropsychologists evaluated each participant in order to establish a diagnosis of MCI, normal cognition, or dementia.
After comparing people's fat intakes to their diagnoses, the Mayo team's analysis showed that the risk of MCI was lower among those with lowest intake of saturated fats and highest intakes of unsaturated fats.
Compared to the people with the lowest intake of unsaturated fats, the odds of having MCI were significantly lower among those with the highest intakes of polyunsaturated fats (omega-3 + omega-6 fats) or combined mono- and polyunsaturated fats.
And, unsurprisingly, the risk of MCI was lowest of all among those with the highest omega-3 intakes.
Thus, as the Mayo Clinic team wrote, “In this study, higher intake of PUFA and MUFA [unsaturated fats] was associated with a reduced likelihood of MCI…” (Roberts RO et al. 2010).
Dr. Roberts made a key point… and expressed a caveat:
“Our findings suggest that the higher intake of monounsaturated and polyunsaturated fatty acids in contrast to saturated fatty acids may have a role in reducing the risk of mild cognitive impairment and, ultimately, of dementia. The association of these fatty acids with mild cognitive impairment in the present study is not definitive …” (MC 2011)
While perhaps not definitive, these results support other indications that unsaturated fats (especially omega-3s) deter dementia while excess intake of saturated fats promotes the disease.
Engelhart MJ, Geerlings MI, Ruitenberg A, Van Swieten JC, Hofman A, Witteman JC, Breteler MM. Diet and risk of dementia: Does fat matter?: The Rotterdam Study. Neurology. 2002 Dec 24;59(12):1915-21.
Eskelinen MH, Ngandu T, Helkala EL, Tuomilehto J, Nissinen A, Soininen H, Kivipelto M. Fat intake at midlife and cognitive impairment later in life: a population-based CAIDE study. Int J Geriatr Psychiatry. 2008 Jul;23(7):741-7.
Mayo Clinic (MC). Diet May Lower Risk of Cognitive Impairment, Mayo Clinic Researchers Find. Tuesday, January 25, 2011. Accessed at http://www.mayoclinic.org/news2011-rst/6152.html
Roberts RO, Cerhan JR, Geda YE, Knopman DS, Cha RH, Christianson TJ, Pankratz VS, Ivnik RJ, O'Connor HM, Petersen RC. Polyunsaturated fatty acids and reduced odds of MCI: the Mayo Clinic Study of Aging. J Alzheimers Dis. 2010;21(3):853-65.
Solfrizzi V, Colacicco AM, D'Introno A, Capurso C, Del Parigi A, Capurso SA, Argentieri G, Capurso A, Panza F. Dietary fatty acids intakes and rate of mild cognitive impairment. The Italian Longitudinal Study on Aging. Exp Gerontol. 2006 Jun;41(6):619-27. Epub 2006 May 12.
Solfrizzi V, Colacicco AM, D'Introno A, Capurso C, Torres F, Rizzo C, Capurso A, Panza F. Dietary intake of unsaturated fatty acids and age-related cognitive decline: a 8.5-year follow-up of the Italian Longitudinal Study on Aging. Neurobiol Aging. 2006 Nov;27(11):1694-704. Epub 2005 Oct 26.
Solfrizzi V, Frisardi V, Capurso C, D'Introno A, Colacicco AM, Vendemiale G, Capurso A, Panza F. Dietary fatty acids in dementia and predementia syndromes: epidemiological evidence and possible underlying mechanisms. Ageing Res Rev. 2010 Apr;9(2):184-99. Epub 2009 Jul 28. Review.