Eating too much steak and bacon may increase the risk of dementia later in life, a controversial government-funded study suggests.
Harvard researchers looked at 133,000 adults over four decades and assessed how much processed and unprocessed red meat they ate on average per day.
They found that eating one serving of processed red meat (about two slices of bacon or a single sausage) was linked to a 13 percent increased risk of dementia.
The study concluded that someone could reduce their risk of developing dementia by 28 percent by replacing one daily serving of processed red meat with the same amount of fish.
The team’s most controversial finding was that consuming at least one serving of unprocessed meat (a sirloin, 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, consumed in excess, is linked to colon cancer due to chemicals added to meat as preservatives or produced when it is cooked.
But the Mass General Brigham team says there is evidence that eating too much processed red meat can also contribute to dementia.
Experts have also cited flaws in recent research on unprocessed red meat, suggesting that it only shows observations and does not take into account other lifestyle factors.
A new study suggests that red and processed meats may increase the risk of dementia and cognitive decline. However, red meat was associated with self-reported cognitive decline rather than an actual increase in dementia diagnoses.

The study also did not look at steak, one of the most common unprocessed meats in the United States.
The study results should be taken 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 looked at people who answered detailed questions about their diet every two to four years, and who were followed for dementia for decades, up to 43 years.
Processed red meat contains nitrites, added as preservatives to prevent spoilage, which can cause molecules called free radicals to get out of control and damage the brain.
The high salt content of foods like bacon can also cause high blood pressure, damage blood vessels, reduce blood flow to the brain, and lead to vascular dementia, the second most common type of dementia.
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The study, published in the journal Neurologyanalyzed data on health professionals in the US who enrolled in research studies in midlife.
Nearly 12,000 of these people developed dementia, and nearly 17,500 volunteers underwent telephone assessments to judge their cognitive function, including memory, language skills and thinking speed.
People’s scores on these assessments were used to calculate their “brain age” for thinking skills, and people who ate too much red meat could compare their brain age to others.
The results suggested that a person’s brain was about 20 months older, based on cognitive function, for each extra serving of processed red meat they ate per day.
One serving 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, functioning like the equivalent of a brain 20 months older, for each additional daily serving of processed red meat.
The researchers also looked at people’s self-reported cognitive problems, based on answers to questions such as whether they had difficulty remembering people or whether they had recently gotten lost.
These self-reports are less reliable than an expert’s assessment, but people who report thinking problems are often right about it and are later diagnosed with cognitive impairment or dementia.
People who ate at least a quarter of a serving of processed red meat daily were 14 percent more likely than those who ate a tenth of a serving on average to report cognitive problems.
The results also suggest that too much unprocessed red meat, such as beef and lamb, could have an effect on thinking skills.

The graph above shows Alzheimer’s rates per 100,000 people, both age-standardized and for all ages. Age-standardized is a method used to adjust for differences in age distribution between populations or over time, while non-age-standardized is the crude rate calculated across all age groups of the population without any adjustment.

The study found a higher prevalence of dementia in those who ate more processed meats such as bacon and sausages. However, red meat did not have the same effect.
Self-reported cognitive decline was 16 percent more likely in people who ate at least one daily serving of unprocessed red meat on average, compared to those who ate less than half a serving.
However, no increased risk of being diagnosed with dementia was found related to unprocessed red meat.
All of the study’s findings came after taking into account factors that could increase people’s risk of dementia, such as weight, physical activity, and family history of dementia.
Red meat, when digested in the body, produces a substance called trimethylamine N-oxide (TMAO), which some scientists believe may contribute to the protein buildup in the brain seen in dementia.
However, this is based solely on animal studies, not humans.
Dr Wang said: “Reducing the amount of 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 8 million Americans suffer from some form of dementia, and about 500,000 new cases are diagnosed each year.
Diagnoses are also expected to increase from 60,000 in 2020 to 179,000 per year in 2060.
Dementia also affects almost 1 million Britons and it is estimated that one in 11 people over the age of 65 suffer from the condition. The numbers are expected to rise to 1.4 million by 2040, according to the Alzheimer’s Society.

Dr. Peter Attia, surgeon and founder of Early Medical, said research on red meat often doesn’t take into account other lifestyle factors such as smoking and sedentary lifestyle.
The findings come amid recent criticism of studies on the health effects of red meat.
In a recent episode of Gaggernometry PodcastDr. Peter Attia, surgeon and founder of Early Medical, suggested that much of the research linking red meat to negative health outcomes such as dementia and colon cancer could be wrong.
He said: ‘The problem is that epidemiology, especially when risk rates are relatively small, is riddled with errors. Epidemiology only identifies associations, but can never identify causation.
‘One of the big challenges with the epidemiology of red meat is that people who consume it and those who do not consume it tend to be, on average, surrogates for very different behaviors.
He noted that people who consume higher amounts of red meat are also more likely to consume more processed meats, such as jerky and bacon.
However, those who avoid red meat are also more likely to exercise, quit smoking, and add more fruits and vegetables to their diet.
Dr. Attia said, “I think, frankly, there’s more nuance than that and I think it also comes down to the type of red meat that you’re going to consume.” And I don’t think all red meat is the same.
The researchers of the new study said there are several limitations, including reliance on observational data and use of self-reported data to measure cognitive decline.
The study also included primarily white professionals, making the sample size less diverse.