As today marks the 81st birthday of Krispy Kreme – an American doughnut company and coffeehouse chain based in Winston-Salem, North Carolina built off an ancient, secret cajun recipe – it seems a fitting day to talk about obesity, fat, and its effect on the brain. Let’s start with “skinny fat”.
Sarcopenia, which is the loss of muscle mass, tends to happen naturally with age. So, in older people with sarcopenia, excess body fat may not be readily visible. But hidden fat, paired with muscle mass loss later in life, could predict Alzheimer’s risk, researchers warn, and Sarcopenic obesity may exacerbate the risk of other cognitive decline later in life.
A recent study — the results of which have been published in the journal Clinical Interventions in Aging — has found that sarcopenia and obesity (independently, but especially when occurring together) can heighten the risk of cognitive function impairments later in life.
The research was conducted by scientists at the Comprehensive Center for Brain Health at the Charles E. Schmidt College of Medicine of Florida Atlantic University in Boca Raton.
“Sarcopenia,” explains senior study author Dr. James Galvin, “has been linked to global cognitive impairment and dysfunction in specific cognitive skills including memory, speed, and executive functions.”
“Understanding the mechanisms through which this syndrome may affect cognition is important as it may inform efforts to prevent cognitive decline in later life by targeting at-risk groups with an imbalance between lean and fat mass.”
Dr. James Galvin
“They may benefit from programs addressing loss of cognitive function by maintaining and improving strength and preventing obesity,” he adds.
Beware sarcopenic obesity
The scientists analyzed health-related data collected from 353 participants — aged 69, on average — all of whom registered to take part in community-based studies on aging and memory.
To establish whether or not there was a link between sarcopenic obesity — that is, the presence of excess body fat in conjunction with muscle mass loss — and cognitive decline, the team assessed participants’ performance on tests evaluating cognitive function, including the Montreal Cognitive Assessment and animal-naming exercises.
Also, the participants’ muscle strength and mass were evaluated through grip strength tests and chair stands, and they also underwent body compositions assessments, which looked at muscle mass, body mass index (BMI), and the amount of body fat.
The researchers discovered that the participants with sarcopenic obesity had the poorest performance on cognition-related tests. The next poorest performance on cognition tests was seen in people with sarcopenia alone, followed by participants who only had obesity.
Both when occurring independently and when occurring in concert, obesity and loss of muscle mass were linked with impaired working memory — which is the type of memory we use when making spontaneous decisions on a daily basis — as well as less mental flexibility, poorer orientation, and worse self-control.
Keep changes in body composition in check
The scientists explain that obesity could exacerbate the risk of cognitive decline through biological mechanisms that influence vascular health, metabolism, and inflammation.
Moreover, they warn that in people who already face impaired executive functioning, obesity might also impact energy resources through poor self-control that affects nutrition.
As for sarcopenia, the researchers note that it could influence brain mechanisms related to conflict resolution skills and selective attention.
Based on the study’s findings, Dr. Galvin and his colleagues are particularly concerned that a mix of sarcopenia and excess body fat in older adults could become a serious public health issue, so they believe that any significant changes in body mass composition should be closely monitored to prevent negative health outcomes.
“Sarcopenia either alone or in the presence of obesity, can be used in clinical practice to estimate potential risk of cognitive impairment,” notes study co-author Magdalena Tolea.
But such health issues can be kept under control, and the risks associated with them averted, she suggests.
“Testing grip strength by dynamometry can be easily administered within the time constraints of a clinic visit, and body mass index is usually collected as part of annual wellness visits,” concludes Tolea.
How Aging and Obesity Prime the Brain for Alzheimer’s
According to another new study, the effects of natural aging processes, combined with those of obesity and a poor diet, affect certain brain mechanisms, thereby boosting the risk of Alzheimer’s. The new study, conducted on mice, uncovered how a high-fat, high-sugar diet renders the aging brain more vulnerable to Alzheimer’s.
Alzheimer’s disease is a neurodegenerative condition that is characterized primarily by memory loss and impaired cognition. Some risk factors for the development of this disease are aging and metabolic conditions such as obesity and diabetes. However, many of the biological mechanisms underlying the onset and progression of this disease remain unknown.
This is despite the fact that our understanding of the predisposing risk factors is growing all the time. Now, Rebecca MacPherson, Bradley Baranowski, and Kirsten Bott — of Brock University in Ontario, Canada — have conducted a study that has allowed them to uncover some more of the mechanics at play in the development of this type of dementia.
The team worked with aging mice to investigate how a high-fat, high-sugar (HFS) diet that fueled obesity might also prime the brain for neurodegeneration in this sample. Their findings are described in a paper now published in the journal Physiological Reports.
How unhealthful diets impact the brain
Specifically, the researchers examined how an HFS diet, in conjunction with the effects of normal biological aging, would affect insulin signaling, which helps to regulate the amount of glucose (simple sugar) absorbed by muscles and different organs.
They also looked at how this obesity-inducing diet might alter biomarkers relating to inflammation and cellular stress.
To understand the impact of an HFS diet on aging mice, the research team put some mice on a regular type diet, while others were given food that had a high fat and sugar content.
After the mice had been fed their respective diets for a period of 13 weeks, the team looked for signs of inflammation and measured cellular stress levels in two brain areas associated with memory and cognitive behavior: the hippocampus and the prefrontal cortex.
The researchers also compared the effects of an HFS diet on the brains of aging rodents’ baseline measurements effected on the brains of younger mice.
They found older mice on an obesity-inducing diet had high levels of brain inflammation and cellular stress, as well as insulin resistance in parts of the hippocampus linked to the development of Alzheimer’s disease.
Although more markers of insulin resistance were observed in the prefrontal cortices of mice that had been on an HFS diet, inflammation status and cellular stress markers remained the same.
The study authors hypothesize that “region-specific differences between the prefrontal cortex and hippocampus in response to aging with an HFS diet [suggest] that the disease pathology is not uniform throughout the brain.”
Obesity boosts aging’s negative effect
Notably, the researchers also found that brain inflammation levels had also increased in the mice that had been on a regular diet, compared with baseline measurements.
The researchers note that this could be taken as evidence of aging’s role as an independent risk factor in Alzheimer’s. Obesity, they add, boosts the risk by affecting key mechanisms in the brain.
“This study,” they claim, “provides novel information in relation to the mechanistic link between obesity and the transition from adulthood to middle age and signaling cascades that may be related to [Alzheimer’s] pathology later in life.”
“These results add to our basic understanding of the pathways involved in the early progression of [Alzheimer’s] pathogenesis and demonstrate the negative effects of an HFS diet on both the prefrontal cortex and hippocampal regions.”
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Cohut, Maria. ”Skinny fat’ linked to cognitive decline, study warns.” Medical News Today, Friday 6 July 2018
Cohut, Maria. ”Aging, obesity may prime the brain for Alzheimer’s.” Medical News Today, Monday 2 July 2018