International Business Department           Liu Bojia           January 22, 2023

  Readers who pursue a healthy lifestyle know that it's important to "keep your mouth shut". Some people see "sugar" as a scourge and won't touch anything too sweet, while others find "fat" a sin and refuse anything too oily. However, there is another type of food that you really need to watch out for than just sugar and fat, and that is processed foods that are a full blend of carbohydrates and fats - sugar-oil mixtures. Common examples are doughnuts, crisps, milk chocolate, sandwich biscuits, milk tea ......

  Sugar-oil mixtures are not only calorie bombs, but they are also often lured by the lure of "pleasure", making them irresistible to eat. A new study in Cell Metabolism found that sugar-oil mixtures, when consumed, modulate the brain's motivation to eat through the gut-brain pathway. And, when carbohydrates and fats are fully integrated, they work synergistically as "1+1>2", stimulating dopamine release more than eating the same amount of carbohydrates or fats, resulting in a desire to eat again without realising it.

  When we consume sugar or fat, the vagus nerve, which connects our internal organs, transmits information to the brain about the type and concentration of the nutrient. In this study, scientists used cutting-edge technology to directly monitor vagal neuron activity in mice and found that there are two separate gut-brain pathways responsible for the perception of sugar and fat, respectively. In other words, different vagal neurons report back to the brain when sugar or fat is consumed.

  These two pathways go in different directions and both cause dopamine release in the brain's reward centre. The brain feels the pleasure of eating, which in turn induces the mice to seek out food more aggressively and consume more sugar or fat.

  However, when the researchers activated the gut-brain pathway for both sugar and fat, they found that the stimulation brought to the brain was not a simple addition of two parallel pathways, but rather a powerful synergy. "Even when the total calories remained constant, the combination of sugar and oil led to more dopamine release." The authors of the paper describe.

  The result of the increased dopamine release was that the mice developed stronger intrinsic cravings for high-sugar, high-fat foods, and they began to overeat.

  This kind of overeating is hard to control, not only for experimental mice, but I'm afraid it's equally true for humans. Because, as the study authors point out, communication between the gut and the brain occurs below the level of consciousness, and whether or not there is a conscious effort to refrain, there is already an established programme in the brain that prefers to seek out things that are high in sugar and fat, resulting in us unconsciously wanting to eat more sugar-oil mixtures.

  But that doesn't mean we're completely out of control when faced with all the tantalising sugar-oil mixtures in our daily lives. In the researchers' opinion, as we learn more about the effects of gut-brain circuits on appetite, targeting and modulating gut-brain reward circuits will be able to serve as a new way to develop new weight loss strategies to help people curb unhealthy eating habits.