Changes in brain activity after weight loss

Low-calorie diet-induced weight loss is associated with altered brain connectivity and food desire in obesity

OBJECTIVE

The main objective of this study is to better understand the effects of diet-induced weight loss on brain connectivity in response to changes in glucose levels in individuals with obesity.

METHODS

A total of 25 individuals with obesity, among whom 9 had a diagnosis of type 2 diabetes, underwent functional magnetic resonance imaging (fMRI) scans before and after an 8-week low-calorie diet. We used a two-step hypereuglycemia clamp approach to mimic the changes in glucose levels observed in the postprandial period in combination with task-mediated fMRI intrinsic connectivity distribution (ICD) analysis.

RESULTS

After the diet, participants lost an average of 3.3% body weight. Diet-induced weight loss led to a decrease in leptin levels, an increase in hunger and food intake, and greater brain connectivity in the parahippocampus, right hippocampus, and temporal cortex (limbic-temporal network). Group differences (with vs. without type 2 diabetes) were noted in several brain networks. Connectivity in the limbic-temporal and frontal-parietal brain clusters inversely correlated with hunger.

CONCLUSIONS

A short-term low-calorie diet led to a multifaceted body response in patients with obesity, with an increase in connectivity in the limbic-temporal network (emotion and memory) and hormone and eating behavior changes that may be important for recovering the weight lost.

Intermittent energy restriction changes the regional homogeneity of the obese human brain

Background

Intermittent energy restriction (IER) is an effective weight loss strategy. However, the accompanying changes in spontaneous neural activity are unclear, and the relationship among anthropometric measurements, biochemical indicators, and adipokines remains ambiguous.

Methods

Thirty-five obese adults were recruited and received a 2-month IER intervention. Data were collected from anthropometric measurements, blood samples, and resting-state functional magnetic resonance imaging at four time points. The regional homogeneity (ReHo) method was used to explore the effects of the IER intervention. The relationships between the ReHo values of altered brain regions and changes in anthropometric measurements, biochemical indicators, and adipokines (leptin and adiponectin) were analyzed.

Results

Results showed that IER significantly improved anthropometric measurements, biochemical indicators, and adipokine levels in the successful weight loss group. The IER intervention for weight loss was associated with a significant increase in ReHo in the bilateral lingual gyrus, left calcarine, and left postcentral gyrus and a significant decrease in the right middle temporal gyrus and right cerebellum (VIII). Follow-up analyses showed that the increase in ReHo values in the right LG had a significant positive correlation with a reduction in Three-factor Eating Questionnaire (TFEQ)-disinhibition and a significant negative correlation with an increase in TFEQ-cognitive control. Furthermore, the increase in ReHo values in the left calcarine had a significant positive correlation with the reduction in TFEQ-disinhibition. However, no significant difference in ReHo was observed in the failed weight loss group.

Conclusion

Our study provides objective evidence that the IER intervention reshaped the ReHo of some brain regions in obese individuals, accompanied with improved anthropometric measurements, biochemical indicators, and adipokines. These results illustrated that the IER intervention for weight loss may act by decreasing the motivational drive to eat, reducing reward responses to food cues, and repairing damaged food-related self-control processes. These findings enhance our understanding of the neurobiological basis of IER for weight loss in obesity.

Current Insights into the Potential Role of fMRI in Discovering the Mechanisms Underlying Obesity

Obesity is becoming one of the major global health concerns. This chronic disease affects around 650 million people worldwide and is an underlying cause of a number of significant comorbidities. According to the World Health Organization (WHO) report on obesity from 2022, this disorder became the fourth leading cause of deaths in Europe. Thus, understanding the mechanisms underlying obesity is of essential importance to successfully prevent and treat this disease. The aim of this study was to review the current insights into the potential role of fMRI in discovering the mechanisms underlying obesity on the basis of recent scientific literature published up to December 2022 and searches of the PubMed, Google Scholar and Web of Science databases. The literature assessed indicated that a growing body of evidence suggests that obesity leads to changes in both structure and connectivity within the central nervous system. Emerging data from recent functional magnetic resonance imaging (fMRI) studies prove that obese individuals present an increased motivational drive to eat as well as impaired processing in reward- and control-related brain regions. Apart from this, it is clear that fMRI might be a useful tool in detection of obesity-induced changes within the central nervous system.

Functional Magnetic Resonance Imaging and Obesity-Novel Ways to Seen the Unseen

Obesity remains a pandemic of the 21st century. While there are many causes of obesity and potential treatments that are currently known, source data indicate that the number of patients is constantly increasing. Neural mechanisms have become the subject of research and there has been an introduction of functional magnetic resonance imaging in obesity-associated altered neural signaling. Functional magnetic resonance imaging has been established as the gold standard in the assessment of neuronal functions related to nutrition. Thanks to this, it has become possible to delineate those regions of the brain that show altered activity in obese individuals. An integrative review of the literature was conducted using the keywords ““functional neuroimaging” OR “functional magnetic resonance “OR “fmri” and “obesity” and “reward circuit and obesity” in PubMed and Google Scholar databases from 2017 through May 2022. Results in English and using functional magnetic resonance imaging to evaluate brain response to diet and food images were identified. The results from functional magnetic resonance imaging may help to identify relationships between neuronal mechanisms and causes of obesity. Furthermore, they may provide a substrate for etiology-based treatment and provide new opportunities for the development of obesity pharmacotherapy.

Milk fat globule membrane attenuates high fat diet-induced neuropathological changes in obese Ldlr-/-.Leiden mice

BACKGROUND

Milk-fat globule membrane (MFGM) is a complex structure secreted by the mammary gland and present in mammalian milk. MFGM contains lipids and glycoproteins as well as gangliosides, which may be involved in myelination processes. Notably, myelination and thereby white matter integrity are often altered in obesity. Furthermore, MFGM interventions showed beneficial effects in obesity by affecting inflammatory processes and the microbiome. In this study, we investigated the impact of a dietary MFGM intervention on fat storage, neuroinflammatory processes and myelination in a rodent model of high fat diet (HFD)-induced obesity.

METHODS

12-week-old male low density lipoprotein receptor-deficient Leiden mice were exposed to a HFD, a HFD enriched with 3% whey protein lipid concentrate (WPC) high in MFGM components, or a low fat diet. The impact of MFGM supplementation during 24-weeks of HFD-feeding was examined over time by analyzing body weight and fat storage, assessing cognitive tasks and MRI scanning, analyzing myelinization with polarized light imaging and examining neuroinflammation using immunohistochemistry.

RESULTS

We found in this study that 24 weeks of HFD-feeding induced excessive fat storage, increased systolic blood pressure, altered white matter integrity, decreased functional connectivity, induced neuroinflammation and impaired spatial memory. Notably, supplementation with 3% WPC high in MFGM components restored HFD-induced neuroinflammation and attenuated the reduction in hippocampal-dependent spatial memory and hippocampal functional connectivity.

CONCLUSIONS

We showed that supplementation with WPC high in MFGM components beneficially contributed to hippocampal-dependent spatial memory, functional connectivity in the hippocampus and anti-inflammatory processes in HFD-induced obesity in rodents. Current knowledge regarding exact biological mechanisms underlying these effects should be addressed in future studies.

Obesity and Brain Function: The Brain-Body Crosstalk

Dementia comprises a wide range of progressive and acquired neurocognitive disorders. Obesity, defined as excessive body fat tissue, is a common health issue world-wide and a risk factor for dementia. The adverse effects of obesity on the brain and the central nervous system have been the subject of considerable research. The aim of this review is to explore the available evidence in the field of body-brain crosstalk focusing on obesity and brain function, to identify the major research measurements and methodologies used in the field, to discuss the potential risk factors and biological mechanisms, and to identify the research gap as a precursor to systematic reviews and empirical studies in more focused topics related to the obesity-brain relationship. To conclude, obesity appears to be associated with reduced brain function. However, obesity is a complex health condition, while the human brain is the most complicated organ, so research in this area is difficult. Inconsistency in definitions and measurement techniques detract from the literature on brain-body relationships. Advanced techniques developed in recent years are capable of improving investigations of this relationship.

Whole-brain functional connectivity correlates of obesity phenotypes

Dysregulated neural mechanisms in reward and somatosensory circuits result in an increased appetitive drive for and reduced inhibitory control of eating, which in turn causes obesity. Despite many studies investigating the brain mechanisms of obesity, the role of macroscale whole‐brain functional connectivity remains poorly understood. Here, we identified a neuroimaging‐based functional connectivity pattern associated with obesity phenotypes by using functional connectivity analysis combined with machine learning in a large‐scale (n ~ 2,400) dataset spanning four independent cohorts. We found that brain regions containing the reward circuit positively associated with obesity phenotypes, while brain regions for sensory processing showed negative associations. Our study introduces a novel perspective for understanding how the whole‐brain functional connectivity correlates with obesity phenotypes. Furthermore, we demonstrated the generalizability of our findings by correlating the functional connectivity pattern with obesity phenotypes in three independent datasets containing subjects of multiple ages and ethnicities. Our findings suggest that obesity phenotypes can be understood in terms of macroscale whole‐brain functional connectivity and have important implications for the obesity neuroimaging community.