The Western Style Diet, sometimes referred to as Standard American Diet (SAD), is a dietary pattern characterized by high intake of refined carbohydrates, fatty meats, added fats, and sodium, and low intake of whole grains, fruits, and vegetables. The Western dietary pattern has been implicated in the pathogenesis of many chronic diseases and conditions, including overweight and obesity, type 2 diabetes, high blood pressure, and heart disease. Findings from a recent study suggest that the Western dietary pattern impairs hippocampus-dependent learning and memory and drives loss of appetite control.

The hippocampus is a small organ located within the brain’s medial temporal lobe. It is associated primarily with memory (in particular, the consolidation of short-term memories to long-term memories), learning, and spatial navigation. Data from rodent studies suggest that adherence to a Western dietary pattern impairs hippocampal-dependent learning and memory (HDLM). The hippocampus also plays a role in food intake by regulating appetite. Altered hippocampal function subsequent to exposure to a Western-style diet may create a vicious cycle state that promotes increased consumption of unhealthy foods that, in turn, drives further hippocampal dysfunction.

The study involved 110 lean, healthy Australian adults between the ages of 17 and 35 years who adhered to a healthy, non-restrictive dietary pattern. The authors of the study randomized the participants to either a one-week Western-style diet intervention group or a habitual-diet control group.

On the first and eighth days of the study, the participants in the Western diet group ate a breakfast that included a toasted sandwich and a milkshake (high in saturated fat and added sugar). On the second through seventh days of the study, the participants ate two Belgian waffles for either breakfast or dessert for four of the study days. On the other two study days, they obtained their main meal and a drink or dessert from a set of options from a popular fast-food chain. They followed their normal dietary pattern for all other meals. The participants in the control group ate a breakfast consisting of a toasted sandwich and a milkshake (low in saturated fat and added sugar) on the first and eighth days and followed their normal diet for all other meals.

The authors of the study assessed the participants' HDLM function as well as their appetite control before and after the intervention and control periods and again at a three-week follow-up assessment. They found that among those who followed the Western-style diet, HDLM performance declined, compared to the control group. Their appetite control declined as well, and this was strongly correlated with HDLM decline.

These findings suggest that even short-term consumption of a Western-style diet may impair learning and appetite control due to impaired hippocampal function. This lack of appetite control could promote overeating and drive weight gain.

• Link to full study.