Lost in Translation? On the Need for Convergence in Animal and Human Studies on the Role of Dopamine in Diet-Induced Obesity

Abstract

Purpose of Review Animal and human studies suggest that diet-induced obesity and plasticity in the central dopaminergic system are linked. However, it is unclear whether observed changes depend on diet or obesity, and whether they are specific to brain regions and cognitive functions. Here, we focus on neural and cognitive changes in frontostriatal circuits. Recent Findings Both diet and obesity affect dopaminergic transmission. However, site and direction of effects are inconsistent across species and studies. Non-specific changes are observed spanning all frontostriatal loops, from sensory input to motivated behaviour. Given the impact of peripheral signals on central dopaminergic signalling and the interaction between the frontostriatal loops, modulation of dopamine likely propagates through all loops and, thus, affects behaviour on various levels of complexity. Summary To improve convergence between animal and human studies on diet-induced obesity, animal studies should include sophisticated cognitive measures and diets resembling human obesogenic diets, and human studies should adopt diet interventions and longitudinal designs.

Preliminary evidence for an association between intake of high‐fat high‐sugar diet, variations in peripheral dopamine precursor availability and dopamine‐dependent cognition in humans

“…However, translating the findings obtained from animal studies to humans has to be carried out with great care because of the large knowledge gap between the fields. 32 To date, a possible relationship between HFS diets and the dopamine system has not been investigated in humans. Here, we aimed to obtain evidence indicating that a high (relative to low) dietary intake of saturated fat and free sugars is associated with alterations of central dopamine and dopamine-dependent cognition, particularly, reinforcement learning and working memory.…”

“…Taken together, HFS diets may thus be responsible for the observed differences in adaptive behaviour that crucially rely on the neurotransmitter dopamine and that promote the overconsumption of such food products and obesity. However, translating the findings obtained from animal studies to humans has to be carried out with great care because of the large knowledge gap between the fields 32 . To date, a possible relationship between HFS diets and the dopamine system has not been investigated in humans.…”

Relating goal-directed behaviour to grazing in persons with obesity with and without eating disorder features

“…Future research should seek to incorporate other cognitive elements that may influence the relationship between high weight and goal-directed behaviour, such as inhibition, cognitive restraint [65], impulsivity, cognitive load, reward sensitivity; it should consider the role of inflammatory markers and/or appetite-regulating hormones [66]; and it should use in vivo tasks, e.g. experimental paradigms using actual food, or using ecological momentary assessment methods.…”

“…The link between grazing and other eating patterns on the "compulsive eating" spectrum (such as binge eating) should be further investigated and clarified, especially given shared components. Severity and duration of obesity should also be taken into account [66], and overweight groups should also be included (or BMI included as a continuous predictor), to examine potential graded effects of weight; other measures of adiposity (such as waist circumference) should also be considered in addition to BMI, or composite indices (e.g. Janssen et al [17]).…”

Mind over food

“…Here, it was stated that the involved brain-regions as well as the direction of effects varied highly over studies, which led the authors to conclude that "… the pattern emerging from studies comparing obese individuals and binge-eaters with controls is most remarkable for its variability and inconsistency "(p.283) (Ziauddeen et al, 2012). Likewise, a recent review also emphasized the inconsistency of evidence for the dopaminergic system involvement in the neurocognitive profile of obesity (Janssen et al, 2019). Taken together, the idea of increased anticipatory reward neural responding in people with overweight as compared to healthy weight is not supported by solid consistent empirical evidence.…”