The Link Obesity and Cognition
Review on Obesity-related Cognitive Impairment and the Interconnection of Associated Causal Factors.
IMAGE DESCRIPTION:
Both excess WAT in OBESITY, and altered Gut Microbiota, have a direct and indirect Effect on Cognitive Function.
OBESITY AND DYSFUNCTIONAL WAT (White Adipose Tissue) secrete Pro-Inflammatory Adipokines in the circulation, leading to a more pro-inflammatory state. Adipokines affect Vascular Health via promoting Atherosclerosis, Hypertension, and Thrombosis.
GUT MICROBIOTA IN OBESITY is linked to higher levels of LPS (Lipopolysaccharides) and increased Gut Permeability, which may contribute to increase Systemic Inflammation.
Both excess WAT (White Adipose Tissue), and altered Gut Microbiota add to Blood-Brain Barrier (BBB) Dysfunction, which leads to INCREASED NEUROINFLAMMATION, amongst others.
HYPOTHALAMUS, AMYGDALA, AND HIPPOCAMPUS are the most vulnerable regions for Obesity-Related Changes, and all of them are Highly Important in Cognitive Functioning. This is why Cognition is one of the Brain Functions First affected by Neuroinflammation.
All of these Interconnected Factors in Obesity leads finally to Cognitive Impairment.
KEY POINTS
Obesity affects Cardiovascular and Metabolic Health, as well as the Structure and Function of the Brain.
Different studies in humans have demonstrated Associations between Gut Microbiota and Cognition.
Obesity is associated with GM (Grey Matter) and WM (White Matter) REDUCED volume in the Brain.
Midlife Obesity is associated with both Cognitive Impairment and an increased Risk of Developing Dementia later in life.
Excess of WAT in Obesity produces Pro-inflammatory Adipokines, leading to Low-Grade Systemic Peripheral Inflammation, which is associated with Decreased Cognition.
WHR (Waist-Hip Ratio) and WC (Waist Circumference) are more sensitive than BMI for detecting Visceral Obesity (Increased VAT) causing Cognitive Dysfunction.
SUMMARY
The prevalence of Adult Obesity around the World is constantly increasing despite efforts to control it. According to WHO (2022), over 1 Billion people Worldwide suffer from Obesity, including 650 million Adults.
There is no doubt that Obesity negatively impacts Cardiovascular and Metabolic Health, but it also affects the structure and function of the Brain.
In addition to Grey and White Matter Integrity Loss, it leads to Diminished Cognitive Function, including executive function, memory, inhibition, and language.
Even more, it has been found that Midlife Obesity is associated both with Cognitive Impairment and an Increased Risk of Developing Dementia later in life. However, despite research, the specific underlying mechanisms are yet unclear.
This review discusses the contributions of Gut Microbiota, WAT (White Adipose Tissue), Inflammation, and Cerebrovascular Factors, with special attention to changes in Brain Structure and Cognitive Function in Obesity.
Obesity Impact on Cognitive Function: Review of Mechanisms.
To better understand the complex association of factors that cause Cognitive Impairment in Obesity, let us see some Highlights of the events that lead to this Cognitive affectation below. (See also Image Description above.)
Brain Structure in Obesity
Obesity is associated with GM (Grey Matter) and WM (White Matter) REDUCED volume in the Brain, and increases in Waist-to-Hip Ratio (WHR ) during Midlife Obesity are associated with Decreasing Total Brain Volume 10 years later.
Additionally, adults experiencing Obesity show Lower Hippocampal and Hypothalamic Volumes compared to adults with a BMI below 25 kg/m2.
Obesity is associated with an Altered Microstructure of the Brain, with Decreased Executive Functioning and Memory Performance in Older Adults.
Likewise, Obesity is associated with WMH (White Matter Hyperintensities) shown by MRI (Magnetic Resonance Imaging) in the Brain, which are markers of Cerebral Small Vessel Disease. WMH is also associated with Increased Inflammation in the Hypothalamus.
The Blood-Brain Barrier (BBB) also shows Increased Permeability, allowing among others, Peripheral Pro-inflammatory Markers to access the Brain, leading to Neuroinflammation.
Overall, Obesity shows a Negative Impact on the Brain, including Reduced Brain Volumes, with WM and GM Integrity Loss.
Obesity and Cognition
Diverse Research has focused on the Association between Obesity and Cognitive Function.
Research has found that being Overweight or Obese is associated with Decreased Attention, Processing Speed, Motor Function, and Executive Function.
WHR (Waist-Hip Ratio) and WC (Waist Circumference) are measures of Abdominal Obesity and show different associations with Cognition compared to BMI (Body Mass Index).
WHR and WC are more sensitive than BMI for detecting Visceral Obesity (Increased VAT) causing Cognitive Dysfunction.
BMI does not discriminate between the Weight of Muscles and Fat, while WC - waist circumference does not give a complete picture of fat distribution.
WHR (Waist-Hip Ratio) gives more information about the distribution of fat across the body.
A Higher BMI in Midlife is positively associated with Cognitive Decline and Increased Risk of Dementia later in life.
On the other hand, WC has been shown to have a stronger association with Cognition and Cognitive Impairment than BMI.
In recent years, more attention has been paid to the use of different Obesity Indices to assess possible effects on Cognitive Function.
Visceral Adipose Tissue - VAT and SCAT (Subcutaneous Adipose Tissue) contain Different Levels of Inflammatory Markers.
This may explain why different Obesity Indices, such as WC, are Highly Associated with Metabolic Disorders and Cognitive Impairment, compared with BMI.
In support of all these Observations, Weight Loss Studies have shown Cognitive Improvement after Bariatric Surgery.
Overall, there is a consistent link found in the Literature between Obesity Indices and Cognitive Function.
Gut Microbiome in Obesity and Cognition
One of the proposed mechanisms between Obesity and Cognitive Function concerns the Gut Microbiome. An Excess of WAT and altered gut microbiota affect Brain Functioning.
Gut microbiota and Gut Permeability are associated with Peripheral and Central Inflammation.
Obesity increases macrophage infiltration and expression of Pro-inflammatory Cytokines in Circulating Blood.
Likewise, the increase in Gram-negative bacteria in the Microbiome during Obesity increases Gut Permeability and leads to Inflammation by stimulating the production of Pro-inflammatory Cytokines by Visceral Adipose Tissue mainly, thereby activating the innate Immune System.
Adults with Obesity showed Increased Gut Permeability and a distinct microbiome composition compared to lean adults, which was associated with Inflammation. In addition, different studies in humans have demonstrated Associations between Gut Microbiota and Cognition.
Research has shown Healthy Eating patterns can improve both Microbiota Diversity and Inflammation, in the Blood as well as in WAT.
See the Image Below »
To mini-summarize the Mechanism of this chain of events that leads to Cognitive Impairment in Obesity, we can say:
Both excess WAT and altered Gut Microbiota in Obesity contribute to Systemic Inflammation, driving Increased Permeability of the BBB (Blood-Brain Barrier).
Ultimately, this leads to increased Neuroinflammation and subsequent Neurodegeneration including Cognitive Impairment.
Cerebrovascular Function in Obesity
Obesity and increased VAT (Visceral Adipose Tissue, made up of WAT) are Highly Associated with Hypertension and Atherosclerosis, and Vascular Health may be an important Mediator in the link between Obesity and Cognitive Function.
Especially VAT (Visceral Adipose Tissue/ Visceral Obesity), is associated with Dysregulated Adipokine Production and consequently Inflammation and Vascular Disease.
Multiple studies have shown associations between comorbidities of Obesity (such as Hypertension), and Cognitive Impairment.
Additionally, in studies with humans, Adults with Obesity showed significantly Reduced Cerebrovascular Reactivity compared to Lean Adults.
These findings are associated with Impaired Cognition and an Increased Risk of Dementia.
The Obesity-associated changes in Inflammation and Vascular Function might lead to Increased BBB permeability, which is associated with Increased Inflammation, macrophage infiltration, and Cognitive Impairment.
- As has been seen above, Obesity affects Cardiovascular and Metabolic Health, as well as the Structure and Function of the Brain. However, more Research is needed to study Cognitive Changes in Obesity over time.
See Full Article at »
Gut Microbiome, Inflammation, and Cerebrovascular Function: Link Between Obesity and Cognition. https://www.frontiersin.org/articles/10.3389/fnins.2021.
WHO World Obesity Day 2022. https://www.who.int/news/item/04-03-2022-world-obesity-day-2022-accelerating-action-to-stop-obesity