The Paper for the Month for November is from Nutrition Research Reviews (NRR) and is entitled ‘Obesity and dietary fat influence dopamine neurotransmission: exploring the convergence of metabolic state, physiological stress, and inflammation on dopaminergic control of food intake' by Conner W. Wallace, PhD.
After a long, hard day - taking care of the kids, going to work or school, keeping up the house - would you rather sit down for a snack or to a large, satisfying meal? When we eat, our bodies receive necessary fuel, but food does more than provide nutrients. Food is a natural reward that makes us feel good, and there is a greater variety of foods available now than ever before. However, stress from day-to-day life and internal stressors interact with what we choose to eat. Within this context, we can explore how acute or chronic stress alter food intake behaviours that may contribute to the increasing prevalence of obesity worldwide.
Eating foods rich in fat and sugar activates the dopamine system in our brains that control pleasure, learning, and motivation. However, the development of obesity triggers internal stressors like inflammation that also affects dopamine. Inflammation is a natural response of our immune system, but chronic inflammation may be harmful. When eaten frequently, saturated fat can directly trigger inflammation, and over many years, high saturated fat intake could diminish rather than promote dopamine signalling. Thus, stress and diet interact and have the potential to dampen dopamine over time, thereby heightening the feel-good impact of high-calorie foods that elicit a short-term dopamine response.
Most people have heard of “fight-or-flight.” This stress response inhibits digestion but heightens heartrate, breathing, and attention needed to survive momentary stressful events. However, when this system is activated frequently and repeatedly, the brain responds by promoting urges to eat. As an example, if a tiger is about to pounce, we should not be thinking about dinner, but if our daily stress makes us feel anxious, eating is one solution that makes us feel better. A related system involves kappa opioid receptors in the brain. These receptors are activated by stress to alleviate pain but also act to reduce dopamine levels. This results in a vicious cycle by which chronic stress inhibits dopamine and makes high-calorie foods more desirable, thus promoting eating, weight gain, inflammation, and potentially more stress.
When stress and diet interact to promote food intake and weight gain, individuals with chronic inflammation caused by the development of obesity may experience greater responses to low-level stressors. Therefore, it is possible that replacing preferred calorie-rich foods high in saturated fat with potentially less familiar or preferred fruits, vegetables, beans, and whole grains as a lifestyle intervention could present a very real stressor to someone accustomed to less healthy food choices. If this change activates stress systems and dampens the dopamine system, weight loss could be quickly thwarted without proper support and counselling.
Interested in learning more about Obesity and Neuroscience? Register for the Nutrition Society Winter Conference on the topic of Obesity and the brain here