“Processed food” doesn’t conjure up a mental image of a nutritious, well-balanced meal. Rather, boxes of cereal, tubs of margarine, and plastic-wrapped, grey-pink bologna are more likely to come to mind.
The logic goes that the less processed the food, the healthier it is — but not all processed foods are created equal. A new study shows eating one kind of processed food that’s central to Western diets could lead to more worrying health effects than just skyrocketing cholesterol or a post-lunch sugar crash.
In a new study published in the American Journal of Clinical Nutrition, researchers lay out compelling evidence linking the consumption of processed meat with dementia, a group of conditions marked by damage to brain function, later in life.
Huifeng Zhang is the lead author of the study and a postgraduate researcher at the Nutritional Epidemiology Group at the University of Leeds. She tells Inverse the study represents a scientific first.
“As far as we know, this is the first study that investigated associations between specific meat types including processed meat and risk of incident dementia,” Zhang says.
HOW THIS AFFECTS LONGEVITY — Using data from a long-term study that followed adults over a long period of time and tracked their nutrition, the researchers found that the people who had reported eating the most processed meat were also the most likely to be diagnosed with Alzheimer's disease and vascular dementia, which is a form of dementia caused by stroke.
Alzheimer's disease and other forms of dementia can lead to declining cognitive function and behavior problems. According to one study, a diagnosis of Alzheimer's disease reduces life expectancy anywhere from 39-67 percent, depending on age at diagnosis. Conversely, eating unprocessed red meat seemed to confer a “protective” effect — in other words, eating more of these foods was associated with a lower risk for dementia.
There is no cure for dementia, and rates of dementia are increasing around the world. Genes are at least partly responsible for dementia, but environmental factors like diet and exercise can make a difference, too. Understanding what foods contribute to the condition could add to the arsenal of weapons at our disposal to protect against dementia.
SCIENCE IN ACTION — This study presents compelling evidence for a link between processed meat and dementia. It looked at a large group of people over an average of eight years. The scientists used data from the UK Biobank, which is composed of the health information for half a million adults in England, Scotland, and Wales gathered between 2006 and 2010.
The study participants were all asked to complete a baseline questionnaire at the start of the study on their daily eating habits. Later in the study, a smaller group of participants filled out a more detailed survey about what they ate in the preceding 24 hours and repeated the survey once every four months for 16 months in total.
The surveys included questions about how often participants ate different kinds of meat and how much they consumed at each sitting. Bacon, ham, sausages, meat pies, kebabs, burgers, and chicken nuggets went into a “processed” category, while things like chicken, beef, or pork went into an “unprocessed” category.
To establish a link between their eating habits and later dementia, the researchers used hospital intake data and death records from 2016-2017 to identify whom among the participants had been later diagnosed and died from dementia. Those who ate 25 grams of processed meat a day, for example, increased their risk for dementia by 44 percent.
The study doesn’t go so far as to suggest why there is a link between processed meats and dementia, Zhang says. But she has a theory.
“It is our hypothesis that processed meat linked with dementia might be due to nitrates/nitrites based on previous limited studies,” she says.
Indeed, previous research has pointed to a link between nitrates, which are added to processed meats and other foods, and a host of negative health effects. Saturated fats and high sodium in processed meat could also be contributing to the problem — but the evidence backing this idea up is muddy. Zhang says that the next step for researchers is to establish the biological mechanisms behind this pattern.
WHY IT'S A HACK — Previously, Zhang says, there was no clear evidence associating specific types of meat with dementia. And though the researchers didn’t look into whether some processed meats were worse than others — just processed meats as a whole — this finding suggests that eating less processed meat over the course of one’s lifetime could help prevent this kind of cognitive decline.
Whether someone develops dementia or not depends on more than their diet, however. Genes play a role — in fact, the researchers behind this study also looked at whether the processed meat-eaters carried a gene variant, known as APOE ε4, which is thought to predispose carriers to Alzheimer’s disease and other forms of dementia.
People with APOE ε4 were more likely to develop dementia, the study found. But the risk from eating processed meat didn’t change. Among those who ate the most processed meat, they were also more likely to be men, less educated, smokers, overweight, and also tended to eat more saturated fat and fewer vegetables than others in the study.
As for just how much processed meat you’d have to eat to significantly up your risk of developing dementia, it’s unclear.
“General healthy eating guidelines [in the UK] suggest eating less red and processed meat. So that would be a sensible strategy,” Zhang says.
Background: Worldwide, the prevalence of dementia is increasing and diet as a modifiable factor could play a role. Meat consumption has been cross-sectionally associated with dementia risk, but specific amounts and types related to risk of incident dementia remain poorly understood.
Objective: We aimed to investigate associations between meat consumption and risk of incident dementia in the UK Biobank cohort.
Methods: Meat consumption was estimated using a short dietary questionnaire at recruitment and repeated 24-h dietary assessments. Incident all-cause dementia comprising Alzheimer disease (AD) and vascular dementia (VD) was identified by electronic linkages to hospital and mortality records. HRs for each meat type in relation to each dementia outcome were estimated in Cox proportional hazard models. Interactions between meat consumption and the apolipoprotein E (APOE) ε4 allele were additionally explored.
Results: Among 493,888 participants included, 2896 incident cases of all-cause dementia, 1006 cases of AD, and 490 cases of VD were identified, with mean follow-up of 8 y (SD = 1.1). Each additional 25 g/day intake of processed meat was associated with increased risks of incident all-cause dementia (HR: 1.44; 95% CI: 1.24, 1.67; P-trend < 0.001) and AD (HR: 1.52; 95% CI: 1.18, 1.96; P-trend = 0.001). In contrast, a 50-g/d increment in unprocessed red meat intake was associated with reduced risks of all-cause dementia (HR: 0.81; 95% CI: 0.69, 0.95; P-trend = 0.011) and AD (HR: 0.70; 95% CI: 0.53, 0.92; P-trend = 0.009). The linear trend was not significant for unprocessed poultry and total meat. Regarding incident VD, there were no statistically significant linear trends identified, although for processed meat, higher consumption categories were associated with increased risks. The APOE ε4 allele increased dementia risk by 3 to 6 times but did not modify the associations with diet significantly.
Conclusion: These findings highlight processed-meat consumption as a potential risk factor for incident dementia, independent of the APOE ε4 allele.