Cellular Powerhouse Clues: TCA Cycle Disruptions Linked to Fatigue and Low Mood in Obesity

Obesity has long been recognized as more than a metabolic disorder. Beyond its well-documented cardiovascular and endocrine consequences, it is increasingly associated with a heightened vulnerability to neuropsychiatric symptoms, including depression, anxiety, and persistent fatigue. A new translational study published in Translational Psychiatry offers fresh insight into why these mental health burdens so often accompany excess body weight, pointing to an unexpected suspect: the tricarboxylic acid cycle, the metabolic engine at the heart of every cell’s energy production.

The research, led by Cassandra E. Gheorghe and Juliette Montet of the NutriNeuro laboratory at the University of Bordeaux, together with colleagues at INRAE and clinical partners in the Bordeaux region, set out to test whether disruptions in mitochondrial energy metabolism might help explain the comorbidity between obesity and neuropsychiatric symptoms. While chronic low-grade inflammation has been the dominant explanation in the literature for years, the authors argue that additional immunometabolic alterations, particularly those affecting the tricarboxylic acid (TCA) cycle, may play a significant and previously underappreciated role.

The TCA cycle, also known as the Krebs cycle or citric acid cycle, is a sequence of biochemical reactions that takes place inside mitochondria, the organelles often described as cellular power plants. The cycle oxidizes nutrients derived from carbohydrates, fats, and proteins, generating intermediate metabolites such as citrate, succinate, and malate, which feed the electron transport chain that ultimately produces adenosine triphosphate, the universal energy currency of cells. Because the brain is among the most energetically demanding organs in the body, even subtle perturbations in this machinery could, in principle, influence mood, motivation, and the subjective sense of vitality.

To investigate this possibility, the research team adopted a dual approach that combined human clinical data with animal experiments, a design that strengthens the translational relevance of the findings. On the clinical side, they recruited 83 adults with obesity, defined as a body mass index above 30 kilograms per square meter, and measured the circulating levels of TCA cycle metabolites in their blood plasma. Crucially, they did not stop at metabolic measurements. Each participant also completed validated psychometric assessments: the Montgomery-Asberg Depression Rating Scale for depressive symptoms, the state form of the State-Trait Anxiety Inventory for anxiety, and the Multidimensional Fatigue Inventory for fatigue.

The results revealed a striking pattern. Lower levels of circulating TCA cycle metabolites were associated with more severe neuropsychiatric symptoms in the obese participants, with the strongest and most consistent associations observed for fatigue and reduced motivation. In other words, the individuals whose blood showed the most pronounced depletion of these key metabolic intermediates were also the ones reporting the greatest exhaustion and diminished drive. Interestingly, the associations differed across symptom dimensions, suggesting that distinct aspects of the TCA cycle may map onto different neuropsychiatric phenotypes rather than a single undifferentiated state of psychological distress.

Correlation in humans, however, is only half the story. To probe whether these metabolic shifts have a causal or mechanistic connection to behavior, the team turned to a preclinical model. Male C57BL/6J mice were chronically exposed to a high-fat diet, a standard experimental paradigm for inducing obesity and its metabolic consequences. The researchers then assessed depressive-like behavior using the sucrose preference test, which measures anhedonia, the reduced ability to experience pleasure, and the forced swim test, a widely used index of behavioral despair. Anxiety-like behavior was evaluated with the elevated plus-maze, which exploits the natural conflict between a rodent’s curiosity and its aversion to open, exposed spaces.

Alongside these behavioral measures, the team quantified TCA cycle metabolite levels not only in the plasma but also in three discrete brain regions: the striatum, the hippocampus, and the frontal cortex. This regional analysis proved to be one of the most compelling aspects of the study. The preclinical data identified region-specific associations between brain TCA cycle metabolite levels and behavioral outcomes, and these associations appeared to be modulated by exposure to the high-fat diet. Each of the three regions examined plays a distinct role in emotional and motivational processing. The hippocampus is central to stress regulation and is consistently implicated in depression, the frontal cortex governs executive control and mood regulation, and the striatum is a hub of the reward circuitry that underlies motivation and pleasure seeking.

The finding that metabolic signatures in these specific circuits correlate with specific behavioral outputs lends biological plausibility to the human data. A metabolite profile in the striatum that tracks with anhedonia-like behavior, for example, would align neatly with the clinical observation that reduced motivation was among the symptoms most tightly linked to altered circulating metabolites. Although the study, by design, cannot definitively establish causation in humans, the convergence of the clinical and preclinical arms provides what the authors describe as novel evidence linking TCA cycle dysregulation to neuropsychiatric comorbidities in obesity, and it highlights specific metabolites as potential targets of interest for future research.

The implications of this work extend in several directions. First, it reframes obesity-related neuropsychiatric symptoms not merely as psychological reactions to weight, stigma, or social difficulties, but as phenomena with a measurable biochemical substrate rooted in mitochondrial metabolism. Second, it suggests that the long-standing focus on inflammation, while valuable, may capture only part of the immunometabolic picture. Mitochondrial function and inflammatory signaling are deeply intertwined, and metabolites of the TCA cycle themselves act as signaling molecules that can regulate immune cell behavior. Disruptions in the cycle could therefore feed back into the inflammatory processes already implicated in mood disorders, creating a self-reinforcing loop.

Third, the study opens the door to potential biomarker development. If specific circulating TCA cycle metabolites reliably track fatigue and motivational deficits in people with obesity, they could eventually serve as objective markers to identify patients at heightened neuropsychiatric risk, stratify them for targeted interventions, and monitor treatment response. Nutritional, pharmacological, or lifestyle strategies aimed at restoring mitochondrial metabolic function might then be evaluated in a more precise and personalized manner. The work was supported by the French National Research Institute for Agriculture, Food and Environment and by international funding programs dedicated to nutrition and health biomarkers, reflecting a growing institutional commitment to understanding how metabolism shapes mental health.

Important caveats remain. The clinical cohort was modest in size, and cross-sectional associations cannot determine whether reduced TCA cycle metabolite levels precede the neuropsychiatric symptoms or result from them. Fatigue and low motivation can themselves alter eating patterns, physical activity, and sleep, all of which influence mitochondrial metabolism. The preclinical experiments, while informative, used male mice only, leaving open questions about sex differences that are highly relevant given the epidemiology of both obesity and depression. Moreover, the human measurements were restricted to blood, so the extent to which circulating metabolite levels faithfully reflect what is happening inside the brain remains an active area of investigation, even though the animal data on brain-region-specific metabolite profiles provide valuable supporting evidence.

Nevertheless, the study represents a meaningful step forward in a field that has struggled to explain why so many individuals with obesity experience depression, anxiety, and exhaustion that cannot be fully accounted for by inflammation or psychosocial factors. By shining a light on the tricarboxylic acid cycle, the Bordeaux team has connected two research territories that rarely speak to each other: classical mitochondrial biochemistry and modern neuropsychiatric epidemiology. The metabolites they identified as being of potential interest now become candidates for longitudinal studies, intervention trials, and mechanistic follow-up work in both rodents and humans.

As the global prevalence of obesity continues to climb, and with it the burden of obesity-related mental health problems, research of this kind underscores a simple but powerful idea: the health of the mind may depend, in part, on the metabolic health of the cell. The mitochondria that power our muscles and organs also power our brains, and when their core metabolic machinery falters under the chronic metabolic stress of obesity, the consequences may be felt not only on the scale or in blood panels, but in mood, motivation, and the everyday energy needed to live a full life. The next chapter of this research will determine whether restoring the cycle can restore the spirit.

Subject of Research: TCA cycle metabolite disruptions and neuropsychiatric symptoms in obesity

Article Title: Translational evidence of tricarboxylic acid cycle disruptions in obesity: relevance to neuropsychiatric symptoms

Article References: Gheorghe, C. E., Montet, J., Vancassel, S., Amadieu, C., Leyrolle, Q., Dexpert, S., Beau, C., Forestier, D., Ledaguenel, P., Magne, E., Castanon, N., & Capuron, L. (2026). Translational evidence of tricarboxylic acid cycle disruptions in obesity: relevance to neuropsychiatric symptoms. Translational Psychiatry. https://doi.org/10.1038/s41398-026-04476-7

Image Credits: AI Generated

DOI: 10.1038/s41398-026-04476-7

Keywords: obesity, TCA cycle, mitochondria, depression, anxiety, fatigue, metabolites, neuropsychiatry, high-fat diet, immunometabolism, Translational Psychiatry, motivation