Effects of obesity on depression: A role for inflammation and the gut microbiota

doi:10.1016/j.bbi.2017.08.026

Brain, Behavior, and Immunity

Volume 69, March 2018, Pages 1-8

https://doi.org/10.1016/j.bbi.2017.08.026 Get rights and content

Highlights

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Depression is caused by environmental, genetic and psychological factors.
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Consumption of a high-fat diet induces obesity and chronic inflammation in the body.
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The gut microbiota mediates the effects of the diet and influences mood and behavior.
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Modulation of gut microbiota may produce beneficial effects on depression.

Abstract

Depression is a mental disorder associated with environmental, genetic and psychological factors. Recent studies indicate that chronic neuro-inflammation may affect brain physiology and alter mood and behavior. Consumption of a high-fat diet leads to obesity and chronic systemic inflammation. The gut microbiota mediates many effects of a high-fat diet on human physiology and may also influence the mood and behavior of the host. We review here recent studies suggesting the existence of a link between obesity, the gut microbiota and depression, focusing on the mechanisms underlying the effects of a high-fat diet on chronic inflammation and brain physiology. This body of research suggests that modulating the composition of the gut microbiota using prebiotics and probiotics may produce beneficial effects on anxiety and depression.

Introduction

The prevalence of obesity has increased worldwide in recent decades, mainly due to high-calorie diets and sedentary lifestyles (Drewnowski, 2000). The World Health Organization estimates that 39% of the human adult population is overweight and 13% is obese (WHO, 2016). Obesity is not only associated with significant diseases such as type 2 diabetes mellitus, cardiovascular disease, chronic kidney disease and cancer, but also reduces longevity and quality of life (Scully, 2014).

Global surveys indicate that ∼5% of the world population (approximately 300 million people) suffers from mood disorders (WHO, 2017). Depression is a leading cause of disability worldwide and can lead to suicide, which represents the second leading cause of death in people aged between 15 and 29 years (WHO, 2017). Epidemiological data indicate that individuals with obesity have an increased risk of developing mood disorders such as major depressive disorder (MDD), which represents the most prevalent type of depression (Mansur et al., 2015). The relationship between obesity and depression is bi-directional: individuals with depression have a 50% higher risk of developing obesity and, conversely, people with obesity have an increased risk of developing depressive symptoms and manic episodes. Despite the introduction of new antidepressant drugs, many obese patients treated for depression respond poorly to therapy, suggesting that obesity may reduce the efficacy of anti-depression treatment (Woo et al., 2016).

While depression is a multifactorial disease associated with factors such as stress, genetic predisposition and traumatic life events, recent studies indicate that chronic inflammation caused by a high-fat diet (HFD) may play a major role in inducing neuro-inflammation and depression. Notably, the gut microbiota mediates several of the effects of HFD on human physiology, and influences the mood and behavior of the host. We review here recent studies that suggest an association between obesity, the gut microbiota and depression. While the role played by neurological and hormonal systems has been described in previous reviews (Sarkar et al., 2016, Wang and Kasper, 2014), we focus here on the mechanisms underlying the effects of HFD on the immune system and brain physiology.

Section snippets

Obesity and inflammation

Obesity is associated with chronic, low-grade inflammation in peripheral tissues and blood circulation (Gregor and Hotamisligil, 2011). This association was first reported over two decades ago when the pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-α) was found to be elevated in the blood and adipose tissues of obese individuals (Hotamisligil et al., 1995). Reduction of body weight in these subjects improved insulin sensitivity and reduced TNF-α expression in adipose tissues (

Inflammation and depression

Mood disorders are usually classified as depressed or elevated moods (mania), which may occur alone or together, as in bipolar disorder (Angst et al., 2015). Mood disorders such as depression and bipolar disorder are often accompanied by chronic anxiety and stress. While the cause of mood disorders is multifactorial, alterations in specific regions of the brain have been detected in some individuals, including the prefrontal cortex (PFC), amygdala (AMG), hypothalamus (HYP) and hippocampus (HPC)

HFD, brain inflammation and depression

Long-term HFD feeding is known to produce systemic, chronic inflammation in animals and humans (Buckman et al., 2014, Gregor and Hotamisligil, 2011). Rats fed a HFD for 16 weeks show an increased expression of IL-1β, IL-6 and TNF-α in the HYP compared with animals fed a normal diet (De Souza et al., 2005). Notably, HFD feeding reduces expression of tight junction proteins in the choroid plexus and BBB in rats, and may affect brain function by disrupting BBB integrity (Kanoski et al., 2010).

A role for the gut microbiota in obesity-induced depression

The human gastrointestinal tract is inhabited by trillions of microorganisms (Lin et al., 2014). More than 1500 species of bacteria have been identified so far in the human gut, with Bacteroidetes and Firmicutes representing the two predominant phylotypes (Gill et al., 2006). Different studies indicate consistently that the composition of the gut microbiota is different in lean and obese animals (Ley et al., 2005). HFD affects gut microbiota composition, increasing the Firmicutes/Bacteroidetes

Prebiotics and probiotics

Probiotics are living microorganisms that exert beneficial effects on the host (Delzenne et al., 2011). A large body of animal and clinical studies indicate that probiotics reduce body weight gain and inflammation in HFD-induced obesity (Kobyliak et al., 2016). Most of these studies were conducted using bacteria belonging to the genus Lactobacillus and Bifidobacterium.

In 2005, Logan and Katzman proposed the use of probiotics as adjunct therapy in the treatment of depression (Logan and Katzman,

Perspectives and concluding remarks

The studies presented here suggest that reducing obesity-induced neuro-inflammation may lead to beneficial effects on depression (see Fig. 1 for a summary of the pathways linking HFD, the gut microbiota, neuro-inflammation and depression). Modulation of the gut microbiota may thus represent a novel strategy for treating neuro-inflammation and depression. Probiotics, prebiotics, nutraceuticals and other plant and mushroom extracts may be used for the prevention and treatment of obesity and

Conflict of interest statement

YFK is President of Chang Gung Biotechnology Corporation. JDY is Chairman of the Board of Chang Gung Biotechnology Corporation. The authors (except for JS) have applied for patents related to the use of medicinal mushrooms and probiotics to treat human disease.

Acknowledgments

The author’s work is supported by Primordia Institute of New Sciences and Medicine, by grants MOST103-2320-B-182-027-MY3 and MOST103-2321-B-182-014-MY3 from the Ministry of Science and Technology of Taiwan, and grants CMRPD1B0053, CMRPD1C0781-3, CMRPD1E0071-3, CORPD1F0011 and QZRPD132 from Chang Gung Memorial Hospital.

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¹: These authors contributed equally.

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Invited ReviewEffects of obesity on depression: A role for inflammation and the gut microbiota

Highlights

Abstract

Introduction

Section snippets

Obesity and inflammation

Inflammation and depression

HFD, brain inflammation and depression

A role for the gut microbiota in obesity-induced depression

Prebiotics and probiotics

Perspectives and concluding remarks

Conflict of interest statement

Acknowledgments

Psychoneuroendocrinology

Brain Behav. Immun.

J. Biol. Chem.

Biol. Psychiatry

Brain Behav. Immun.

J Hepatol

Cell

Biol. Psychiatry

Nutrition

Am. J. Clin. Nutr.

Psychiatry Res.

J. Lipid Res.

Brain Behav. Immun.

Lancet Gastroenterol. Hepatol.

Brain Behav. Immun.

Med. Hypotheses

J. Affect Disord.

Neurosci. Biobehav. Rev.

Neuroscience

Trends Endocrinol. Metab.

Psychoneuroendocrinology

J. Neuroimmunol.

Prog. Neuropsychopharmacol. Biol. Psychiatry

Trends Neurosci.

J. Biol. Chem.

Neuropharmacology

Brain Behav. Immun.

Biol. Psychiatry

Probiotic treatment protects against the pro-depressant-like effect of high-fat diet in Flinders Sensitive Line rats

Brain Behav. Immun.

Neuropsychiatric manifestations of human leukocyte interferon therapy in patients with cancer

JAMA

Factors controlling permeability of the blood-brain barrier

Cell. Mol. Life Sci.

Classification of mood disorders

Psychiatr. Pol.

Critical role of gut microbiota in the production of biologically active, free catecholamines in the gut lumen of mice

Am. J. Physiol. Gastrointest. Liver Physiol.

The effect of high-fat diet on rat's mood, feeding behavior and response to stress

Transl. Psychiatry

Bone marrow-derived microglia infiltrate into the paraventricular nucleus of chronic psychological stress-loaded mice

PLoS One

Pharmacotherapy of depression: a historical analysis

J. Neural Transm. (Vienna)

Trafficking of Shigella lipopolysaccharide in polarized intestinal epithelial cells

J. Cell Biol.

Serum and plasma BDNF levels in major depression: a replication study and meta-analyses

World J. Biol. Psychiatry

Purinergic signalling and immune cells

Purinergic Signal

Targeting the microbiota-gut-brain axis: prebiotics have anxiolytic and antidepressant-like effects and reverse the impact of chronic stress in mice.

Biol. Psychiatry

Hypothalamic inflammation: a double-edged sword to nutritional diseases

Ann. NY Acad. Sci.

Metabolic endotoxemia initiates obesity and insulin resistance

Diabetes

Changes in gut microbiota control metabolic endotoxemia-induced inflammation in high-fat diet-induced obesity and diabetes in mice

Diabetes

Association between decreased serum tryptophan concentrations and depressive symptoms in cancer patients undergoing cytokine therapy

Mol. Psychiatry

Ganoderma lucidum reduces obesity in mice by modulating the composition of the gut microbiota

Nat. Commun.

Antrodia cinnamomea reduces obesity and modulates the gut microbiota in high-fat diet-fed mice

Int. J. Obes.

The microbiome-gut-brain axis during early life regulates the hippocampal serotonergic system in a sex-dependent manner

Mol. Psychiatry

From inflammation to sickness and depression: when the immune system subjugates the brain

Invited Review
Effects of obesity on depression: A role for inflammation and the gut microbiota