As you know, I like reviewing the science of the links between various things and dementia or Alzheimer’s disease. I found a study that shows a link between inflammatory foods and dementia.
I’m not a big fan of nutrition studies for reasons that I’ll explain later – they are generally hard to interpret, but this one might show us that foods with a higher inflammatory potential are linked to an increased risk of dementia or Alzheimer’s disease.
As I usually do, I will look at the study, summarize the results, and critique it. Then give you my opinion on the research. Spoiler alert — I find the study to be very interesting.
First, what are inflammatory foods?
Some evidence has suggested that certain foods, nutrients, and non-nutrient food components can modulate inflammatory status acutely and chronically. An earlier prospective study in women seemed to show a link between the inflammatory potential of foods and cognitive decline.
Foods and nutrients associated with the inflammatory biomarkers, such as interleukin (IL)-1β, IL-4, IL-6, L-10, tumor necrosis factor (TNF)-α (which cannot be found in bananas, in case you were wondering), and C-reactive protein, were assigned a value and tallied to obtain a diet inflammatory index score. Higher dietary inflammatory index scores indicated a more inflammatory diet.
An anti-inflammatory diet usually contains multiple daily servings of fruits, vegetables, and coffee or tea (surprisingly), along with frequent servings of legumes (beans, peas, peanuts, and related plants). Diets that have less frequent servings of these foods and higher animal fats are considered inflammatory diets.
I have written several times about the so-called Mediterranean diet, which appears to have some positive health benefits and can probably be considered to be an anti-inflammatory diet.
What are dementia and Alzheimer’s disease?
Before I proceed, it’s important to describe Alzheimer’s disease (AD). It is a chronic neurodegenerative disease that usually starts slowly and worsens over time. It accounts for 60-70% of dementia cases, even though the terms are sometimes used interchangeably. Alzheimer’s disease is a form of dementia.
Amyloid plaques, phosphorylated tau tangles, and neurofibrillary tangles are generally easily visible pathologies that can be observed by microscopic analysis of brain tissue from autopsies of those potentially afflicted by AD. These plaques and tangles seem to affect nerve functioning. Despite these observations, the precise pathophysiology, or development, of the disease is not known.
Since amyloid plaques are often identified in patients with Alzheimer’s disease, a large amount of research is focused on attacking those plaques as a way to reverse the effect on nerves which leads to AD.
The causes of AD are unknown (notice how much we do not know about this disease), although it is speculated that it is mostly genetically related, with a large number of genes that underlie this relationship. Despite the internet tropes, there is no rigorous evidence that aluminum causes AD – I wish this belief went away fast.
And since we have no clear understanding of the etiology and pathophysiology of AD, there are few treatments available today for the disease. Some drugs target the amyloid plaques but have not been shown to change the outcomes of AD.
There are a couple of medications that help manage some of the symptoms of the disease, but they are certainly not cures. There are several drugs at the very earliest stages of development that may hold out hope to treat the underlying disease.
One more thing that needs to be made clear. There are no biological tests for dementia or Alzheimer’s disease — usually, you can only find the amyloid plaques and other pathologies in post-mortem autopsies. Unfortunately. in the absence of an autopsy, clinical diagnoses of AD are “possible” or “probable”, based on other findings, such as memory tests and other methods.
Inflammatory foods and dementia – the paper
In a paper published in Neurology on 10 November 2021, researchers analyzed data from 1,059 older adults in the Hellenic Longitudinal Investigation of Aging and Diet (HELIAD), a population-based study that investigates associations between nutrition and age-related cognition in Greece.
Participants had a mean baseline age of 73.1, a mean of 8.2 years of education, and 40.3% were men. Dietary intake was evaluated through a semi-quantitative food frequency questionnaire validated for the Greek population and administered by a trained dietitian.
The researchers found:
- Each unit increase in the dietary inflammatory index scores was associated with a 21% increased risk of dementia over three years.
- Compared to the participants with the lowest inflammatory diet scores, those with the highest scores were 3X more likely to develop dementia.
- People in the first tertile had the lowest inflammatory index scores with a weekly diet that averaged about 20 servings of fruit, 19 servings of vegetables, four servings of legumes, and 11 servings of coffee or tea.
- Those individuals in the third tertile, the lowest third inflammatory index scores, had a weekly average of nine servings of fruit, 10 servings of vegetables, two servings of legumes, and nine servings of coffee or tea.
Although this study may have shown a decrease in the risk of dementia that is linked to the inflammatory score for the diet, these types of studies must be evaluated carefully. There are several points to be considered:
- The food frequency questionnaires are often subject to measurement errors and bias. A lot of nutritional-based studies rely upon the participant’s memory or a diary to ascertain the inflammatory index scores. For example, a participant may misremember what they ate, or, in an attempt to show that they are eating appropriate foods, exaggerate what they consumed.
- Many dietary components, especially spices, and herbs, were not included in the study. Now, I don’t believe that spices and herbs have a major impact on health, but we don’t know from this study.
- The researchers did not test for serum levels of inflammatory biomarkers which should change with an inflammatory diet.
Summary of inflammatory foods and dementia
I find this type of research to be intriguing, but not necessarily conclusive. Can we tell if a diet low in inflammatory foods lowers the risk of dementia?
The problem is that it’s almost impossible to answer this question with a gold-standard, randomized, double-blinded clinical trial. I can’t think of a way to hide, to either the patient or the researcher, whether the participant is getting 20 servings of fruit or just 5 servings. It will be pretty obvious to everyone.
That being said, despite my being a full-fledged carnivore, this study is enough evidence that I’m willing to increase my consumption of fruits, vegetables, and legumes. I’m already good with my coffee and tea consumption.
Although I remain skeptical about these types of diet studies, there are enough of them out there that maybe we should take notice of them. And there are other benefits of 20 servings of fruit and 20 servings of vegetables – maintaining weight or reducing obesity are some of the important ones.
I am not fully convinced that an anti-inflammatory diet is a guaranteed method to prevent dementia, but the benefits, even if small, far outweigh the risks, unless you hate fruits and vegetables.
So, I’m giving this study 2.5 out of 5 stars. It’s intriguing for sure, and it does confirm other studies that diets with low inflammatory scores, like the Mediterranean diet, are linked to reducing the risk of dementia and Alzheimer’s disease.
Citations
- Charisis S, Ntanasi E, Yannakoulia M, Anastasiou CA, Kosmidis MH, Dardiotis E, Gargalionis AN, Patas K, Chatzipanagiotou S, Mourtzinos I, Tzima K, Hadjigeorgiou G, Sakka P, Kapogiannis D, Scarmeas N. Diet Inflammatory Index and Dementia Incidence: A Population-Based Study. Neurology. 2021 Nov 10:10.1212/WNL.0000000000012973. doi: 10.1212/WNL.0000000000012973. Epub ahead of print. PMID: 34759053.
- Dardiotis E, Kosmidis MH, Yannakoulia M, Hadjigeorgiou GM, Scarmeas N. The Hellenic Longitudinal Investigation of Aging and Diet (HELIAD): rationale, study design, and cohort description. Neuroepidemiology. 2014;43(1):9-14. doi: 10.1159/000362723. Epub 2014 Jul 2. PMID: 24993387.
- Hayden KM, Beavers DP, Steck SE, Hebert JR, Tabung FK, Shivappa N, Casanova R, Manson JE, Padula CB, Salmoirago-Blotcher E, Snetselaar LG, Zaslavsky O, Rapp SR. The association between an inflammatory diet and global cognitive function and incident dementia in older women: The Women’s Health Initiative Memory Study. Alzheimers Dement. 2017 Nov;13(11):1187-1196. doi: 10.1016/j.jalz.2017.04.004. Epub 2017 May 19. PMID: 28531379; PMCID: PMC5909961.
- Shivappa N, Steck SE, Hurley TG, Hussey JR, Hébert JR. Designing and developing a literature-derived, population-based dietary inflammatory index. Public Health Nutr. 2014 Aug;17(8):1689-96. doi: 10.1017/S1368980013002115. Epub 2013 Aug 14. PMID: 23941862; PMCID: PMC3925198.
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