July 31, 2024

expert reaction to conference abstract on red meat intake, risk of dementia and cognitive function in US adults

A conference abstract presented at the Alzheimer’s Association International Conference looks at red meat intake and dementia risk.

Dr Richard Oakley, Associate Director of Research and Innovation, Alzheimer’s Society, said:

“Research into diet and the risk of dementia is a major focus of research.  In particular, the effect of eating processed red meat on our health has been a hot topic.

“In this study more people who ate processed red meat went on to develop dementia and had worse memory and thinking skills.  Being an observational study, it’s important to remember that this research doesn’t prove that eating processed red meat is directly related to developing dementia.  It may be that people who avoid processed red meat are generally more health conscious and avoid other unhealthy habits that increase dementia risk.

“The diseases that cause dementia are very complex, and it is unlikely that one food group would make a significant difference.  Instead, we know that what is good for the heart is good for the head and recommend everyone to eat a healthy balanced diet.”

Dr Hilda Mulrooney, Reader in Nutrition & Health, London Metropolitan University, said:

“This is a large and long-term piece of work, with >131,000 participants followed up for 38 years.  A subset of 87,424 participants free from dementia, stroke, cancer or Parkinson’s disease at baseline had their dietary intakes analysed every 2-4 years using food frequency questionnaires to collect data on intakes of red meat, processed red meat (e.g. salami, sausages, bacon) and nuts/legumes (e.g. beans, lentils, peanut butter).  A subset of >43,000 had longitudinal information on subjective cognitive decline collected, while a smaller subset (>17,000) had their cognitive function assessed using the Telephone Interview for Cognitive Status tool.

“A significant association between both processed red meat and red meat consumption and risk of cognitive decline was observed.  For those consuming at least 0.25 servings of processed red meat per day compared to <0.10 servings, a 14% higher risk of subjective cognitive decline was observed.  For those consuming at least 1 serving of unprocessed red meat per day compared with less than 0.5 serving a day, a 16% higher risk of subjective cognitive decline was observed.  On the positive side, those who had one fewer serving per day of processed red meat and instead one more serving of nuts or legumes (e.g. beans) had a 23% lower risk of dementia, fewer years of cognitive aging and a 20% lower odds of subjective cognitive decline.

“This is a large study carried out over a long time period.  However, the information currently available is limited to an abstract.  It is unclear what is meant by ‘subjective cognitive decline’, and while follow up occurred over a long time period, diet was assessed only every 2-4 years, and diets could change a lot during that time period.  This study focused on only some aspects of diet, and there are others which could potentially play a part in risk of cognitive decline.  It is not clear whether any of those were taken into account.  The full paper will be of interest so that the tools and methods used to assess diet and cognitive decline, the characteristics of the study population and factors controlled for, can be understood.

“However, the nature of this study means that only associations can be shown – causality cannot be demonstrated.  Despite this, there is biological plausibility to these observations.

“The findings align with recommendations to replace meat with protein-rich alternatives such as beans and nuts for sustainability reasons – the EAT Lancet commission was clear that meat consumption needs to reduce to benefit planetary as well as human health.  The UK healthy eating guidelines already recommend reducing meat and processed meat consumption and focusing more on non-meat protein sources for health and sustainability reasons – although this study can’t prove cause and effect, its findings are in line with that.  (The UK population though currently fails to meet those recommendations.)”

Prof Kevin McConway, Emeritus Professor of Applied Statistics, Open University, said:

“It’s pretty well impossible to get a clear message from the information that is available so far about this research.  It is a conference paper, and all we have seen so far is a press release, a brief summary of the research, and a diagram.  There isn’t a detailed, peer-reviewed research report, not yet anyway.  Putting out limited information like this isn’t the right way to report science.

“One important problem is that this is an observational study.  The researchers did not assign particular diets to the study participants.  They just recorded what they ate over a number of years, and also recorded whether they were diagnosed with dementia.  In addition, some participants had measurements taken of their cognitive decline over time.  Those who ate larger amounts of red processed meat had a higher rate of diagnosis of dementia than those who ate smaller amounts or none, and those who ate more read processed meat also had higher rates of cognitive decline.

“But whether these results can be used to advise people on what to eat to reduce their risk of dementia or to slow their cognitive decline depends on whether the differences in dementia diagnosis risk and cognitive decline are actually caused by the amount of red processed meat they ate.  There will have been many other differences between those who ate different amounts of red processed meat, apart from their processed meat consumption – for instance, possible differences in other parts of their diet, or in age, ethnicity, or where they live.  Maybe the differences in dementia diagnosis risk and cognitive decline are caused by some of these other factors, and not the processed meat consumption at all.

“In studies like this, the researchers are generally aware of this possibility of other factors intruding so that you can’t tell what causes that.  They would typically make statistical adjustments to try to allow for some other factors.  While that process can never totally eliminate concerns about cause and effect, they might give a clearer idea on what’s going on.  Details of statistical adjustments, or of other ways of investigating cause and effect, are generally recorded in the full research report.  But we haven’t got that, and the limited information that we do have doesn’t tell us what adjustments were made, or what effect (if any) they had on the findings.

“Without that information it’s essentially impossible to evaluate how good this research is.  It does remain possible that eating more red processed meat causes an increase in dementia risk and/or speed up cognitive decline – although we can’t say how big any such increase is without knowing more statistical details.  But what we know so far about the study doesn’t rule out the possibility that the differences in risk are all caused by other factors, and not processed meat consumption at all.

“That’s presumably why the lead author, in her quote in the press release, doesn’t go beyond saying that eating processed red meat “could be a significant risk factor for dementia” or that dietary guidelines “could include recommendations limiting it to promote brain health.”  We can’t evaluate those ‘could‘s further without actually having the details of this research, and also more research on the same topic to investigate how the processed meat might affect brain function.

“That caution, coming from the people who did the research, and have seen the full findings, contrasts with the statements at the top of the press release that “eating about two servings a week of processed red meat raises the risk of dementia”.  We just can’t tell from this sparse information whether it’s the processed meat that causes the observed increase in risk, and it’s not helpful when an association running a conference makes claims like that without giving the necessary evidence.”

Dr Sebastian Walsh, NIHR Doctoral Fellow (researching population-level approaches to dementia risk reduction), University of Cambridge, said:

“Whilst eye-catching, it is difficult to know exactly what to make of these results without seeing the full research paper (currently only a press release and research summary are available).  On the surface, this is a large and long study.  But it isn’t clear how the analysis was done – specifically what other factors were taken into account when looking at this apparent relationship between red meat and dementia.

“Despite a lot of research looking at specific foods and different diseases, the basic public health advice that eating a healthy, balanced diet is good for health is essentially unchanged.  Most people know and accept this.  What is most important is to find ways of supporting people, particularly those from poorer backgrounds, to follow this advice and address the obesity epidemic.”

‘The abstract ‘A Prospective Study of Long-Term Red Meat Intake, Risk of Dementia, and Cognitive Function in US Adults’ by Yuhan Li et al. was presented at the Alzheimer’s Association International Conference.  It was under embargo until 12:00 noon UK time on Wednesday 31 July 2024.

Conference contact: Niles Frantz, Director, News Media Engagement, Alzheimer’s Association; Phone: 312-363-8782 / Office: 312-786-4592 / nfrantz@alz.org

Declared interests

Dr Richard Oakley: “No conflict of interest.”

Dr Hilda Mulrooney: “I have no conflicts of interest to declare.”

Prof Kevin McConway: “I am a Trustee of the SMC and a member of its Advisory Committee.  My quote above is in my capacity as an independent professional statistician.”

Dr Sebastian Walsh: “No COI.”