Western diets rich in fat and sugar promote excess calorie intake and weight gain; however, the underlying mechanisms are unclear. To close this gap, researchers from Germany, Switzerland and the United States performed a randomized, controlled study with normal-weight participants exposed to a high-fat/high-sugar snack or a low-fat/low-sugar snack for 8 weeks in addition to their regular diet.
Using an interventional study in healthy, normal-weight participants, Thanarajah et al. demonstrate that, independent of body weight gain and alterations in metabolic markers, exposure to high-fat/high-sugar food: (i) reduces preferences for low-fat food, (ii) plays a critical role in up-regulating brain responses to anticipation and consumption of highly palatable, energy-dense food, and (iii) has a generalized effect on the neuronal encoding of prediction errors in the context of associative learning and independent of food rewards. Taken together, repeated consumption of high-fat/high-sugar relative to isocaloric low-fat/low-sugar food, and in the absence of changes in body weight or metabolic state, can rewire brain circuits and thereby induce neurobehavioral adaptations. Hence, changing the food environment and reducing the availability of energy-dense high-fat/high-sugar food items is pivotal to combating the obesity pandemic. Image credit: Thanarajah et al., doi: 10.1016/j.cmet.2023.02.015.
All organisms must procure energy to survive. Consequently, many strategies have evolved to optimize the detection, acquisition, use, and storage of energy sources.
For example, environmental signals become associated with nutritional outcomes and are then subsequently employed by organisms as sensory feedforward cues that anticipate future consumption and restoration of energy balance.
A previously neutral sign of your favorite pastry shop, for instance, becomes associated with donut consumption — the sign (or cue) is imbued with the power to shape future complex behaviors to acquire another donut, even in the absence of hunger.
The fundamental link between the sensory feedback and the energetic properties of food has important implications for understanding the processes by which the modern food environment promotes obesity.
First, there is extensive evidence that sensory association learning, and the consequent power of a cue to control behavior (i.e., food cue reactivity),varies considerably across individuals and is associated with risk for weight gain.
Second, many modern processed foods are high in energy density and frequently contain both fat and sugar, which interact to potentiate reinforcement beyond the energetic value.
Modern processed foods are therefore potent reinforcers and, as with drugs of abuse, animal models have shown that their frequent consumption rewires brain circuits, even in offspring born to mothers consuming a high-fat diet during lactation.
“Our tendency to eat high-fat and high-sugar foods, the so-called Western diet, could be innate or develop as a result of being overweight,” said Dr. Sharmili Edwin Thanarajah, a researcher at the Max Planck Institute for Metabolism Research and the University Hospital at Goethe University.
“But we think that the brain learns this preference.”
To test this hypothesis, Dr. Thanarajah and colleagues gave one group of volunteers a small pudding containing a lot of fat and sugar per day for eight weeks in addition to their normal diet.
The second group received a pudding that contained the same number of calories but less fat.
The volunteer’s brain activity was measured before and during the eight weeks.
The brain’s response to high-fat and high-sugar foods was greatly increased in the group that ate the high-sugar and high-fat pudding after eight weeks.
This particularly activated the dopaminergic system, the region in the brain responsible for motivation and reward.
“Our measurements of brain activity showed that the brain rewires itself through the consumption of chips and co,” said Dr. Marc Tittgemeyer, a researcher at the Max Planck Institute for Metabolism Research and the University of Cologne.
“It subconsciously learns to prefer rewarding food.”
“Through these changes in the brain, we will unconsciously always prefer the foods that contain a lot of fat and sugar.”
During the study, the participants did not gain more weight than the volunteers in the control group and their blood values, such as blood sugar or cholesterol, did not change either.
However, the researchers assume that the preference for sugary foods will continue after the end of the study.
“New connections are made in the brain, and they don’t dissolve so quickly,” Dr. Tittgemeyer said.
“After all, the whole point of learning is that once you learn something, you don’t forget it so quickly.”
The team’s paper was published in the journal Cell Metabolism.
Sharmili Edwin Thanarajah et al. Habitual daily intake of a sweet and fatty snack modulates reward processing in humans. Cell Metabolism, published online March 22, 2023; doi: 10.1016/j.cmet.2023.02.015
Source : Breaking Science News