Eating too much steak and bacon may raise the risk of dementia later in life, a controversial government-funded study suggests.
Harvard researchers looked at 133,000 adults for four decades and evaluated how much processed and unprocessed red meat they ate on an average per day.
They found that eating one serving of processed red meat – roughly two slices of bacon or a single sausage – was linked to a 13 percent increased risk of dementia.
The study concluded that someone could cut their risk of getting dementia by 28 percent by replacing a portion a day of processed red meat with the same amount of fish.
The team’s more controversial find was that consuming at least one serving of unprocessed meat – a sirloin steak, ground beef or lamb, for example – was linked to a 16 percent increased chance of cognitive decline, which is a precursor to dementia.
It is well known that processed red meat, eaten to excess, is linked to colon cancer because of chemicals added to the meat as preservatives or produced when it is cooked.
But the team at Mass General Brigham say there is evidence eating too much processed red meat may also contribute to dementia.
Experts have also cited flaws in recent research on unprocessed red meat, suggesting they only show observations and do not account for other lifestyle factors.
A new study suggests red and processed meats may raise the risk of dementia and cognitive decline. However, red meat was associated with self-reported cognitive decline rather than actual increased dementia diagnoses
The study also did not look at steak, one of America’s most common non-processed meats.
The results of the study should be treated with caution, as previous research has not always found a link between red meat consumption and dementia.
But a strength of the new research is that it analyzed people who answered detailed questions on their diet every two to four years, and who were tracked to see if they got dementia for decades – up to 43 years.
Processed red meat contains nitrites, added as preservatives to keep it from going bad, which may cause molecules called free radicals to get out of control and damage the brain.
The high salt content of foods like bacon can also lead to high blood pressure, damaging blood vessels, reducing blood flow to the brain and leading to vascular dementia – the second most common type of dementia.
The study, published in the journal Neurology, looked at data on health professionals in the US who signed up for research studies in middle age.
Almost 12,000 of these people developed dementia, and almost 17,500 female volunteers were given telephone assessments to judge their cognitive function – including memory, language skills and thinking speed.
People’s scores in these assessments were used to work out their ‘brain age’ for thinking skills, and people who ate too much red meat could have their brain age compared with others.
The results suggest someone’s brain was about 20 months older, based on cognitive function, for every extra portion of processed red meat they ate per day.
A portion is approximately three ounces of meat, which is the size of a deck of cards.
People’s verbal memory – their ability to remember words and the details of stories, for example – was worse, working out as the equivalent of a 20-month older brain, for every extra daily portion of processed red meat.
Researchers also looked at people’s self-reported cognitive problems, based on answers to questions such as whether they struggled to remember people or had recently lost their way.
These self-reports are less reliable than an expert assessment, but people who report thinking problems are often right about them, and later diagnosed with cognitive decline or dementia.
People who ate at least a quarter of a portion of processed red meat a day were 14 percent more likely than those who ate a tenth of a portion on average to self-report cognitive issues.
The results also suggest too much unprocessed red meat, like beef and lamb, might have an effect on thinking skills.
The above graph shows rates of Alzheimer’s per 100,000 people, both age-standardized and all ages. Age-standardization is a method used to adjust for differences in age distribution between populations or over time, while non-age-standardized is the raw rate calculated across all age groups in the population without any adjustment
The study found an increased prevalence of dementia in those who ate more processed meats like bacon and sausage. However, red meat did not have the same effect
Self-reported cognitive decline was 16 percent more likely in people eating at least one daily portion of unprocessed red meat on average, compared to those eating less than half a portion.
However no increased risk of being diagnosed with dementia was found linked to unprocessed red meat.
All the findings from the study came after taking into account factors which might increase people’s risk of dementia, such as their weight, physical activity and family history of dementia.
Red meat, when it is digested in the body, produces a substance called trimethylamine N-oxide (TMAO), which some scientists believe may contribute to the build-up of proteins in the brain seen in dementia.
However this is based only on studies involving animals, not humans.
Dr Wang said: ‘Reducing how much red meat a person eats and replacing it with other protein sources and plant-based options could be included in dietary guidelines to promote cognitive health.’
Currently nearly 8million Americans currently have some form of dementia and there are around 500,000 new cases diagnosed per year.
Diagnoses are also expected to rise from 60,000 in 2020 to 179,000 per year by 2060.
Dementia also affects nearly 1million Brits, and it’s estimated one in 11 people over 65 have the condition. Figures are expected to rise to 1.4million by 2040, according to the Alzheimer’s Society.
Dr Peter Attia, a surgeon and founder of Early Medical, said research on red meat often doesn’t account for other lifestyle factors like smoking and sedentary lifestyles
The findings come admid recent criticism of studies on the health effects of red meat.
In a recent episode of the Triggernometry podcast, Dr Peter Attia, a surgeon and founder of Early Medical, suggested much of the research linking red meat to negative health outcomes like dementia and colon cancer could be flawed.
He said: ‘The problem is epidemiology, especially when the hazard ratios are relatively small, is so fraught with errors. Epidemiology only identifies associations, but it can never identify causation.
‘One of the big challenges with the red meat epidemiology stuff is that people consuming red meat and people not consuming red meat tend to be proxies on average for very different behaviors.
He noted that people consume higher amounts of red meat are also more likely to consume more processed meats like beef jerky and bacon.
However, those who steer clear of red meat also are more likely to exercise, quit smoking, and add more fruits and vegetables to their diet.
Dr Attia said: ‘I think there’s more nuance to it than that frankly and I think it also comes down to the type of red meat you’re going to consume. And I don’t think all red meat is created equal.’
The researchers in the new study said there are several limitations, including relying on observational data and using self-reported data to measure cognitive decline.
The study also mainly included white professionals, which made the sample size less diverse.
