The immune system is a complex network of organs and cell types with multiple functions, highly integrated in all body systems. It fights pathogens, repairs damaged tissue, and maintains homeostasis. It continuously interacts with the external environment and a variety of environmental factors. One of these factors is diet. In the past few years, there has been considerable interest in the role that the “Western diet” plays in shaping the immune response.
This diet has been adopted by many populations across the world and appears to correlate with a high incidence of chronic inflammatory disorders, including diabetes, multiple sclerosis and asthma. It includes a large proportion of red meat, sugars, fats and refined carbohydrates, and relatively small amounts of vegetables, fruits and fish. Most likely, these inflammatory disorders are not caused by only one or few components of the Western diet. Rather, it is the complex and unbalanced array of micronutrients in the diet that leads to the development of these disorders.
Now, results from a new study highlight some of the immune system-related effects mediated by the Western diet and, more specifically, by dietary lipids. Dietary lipids, which consist of fatty acids, are a major source of energy and derive from plants and animals. They are essential for growth and development. However, some fatty acids are potentially harmful and play a significant role in the development of obesity. These include saturated fats and trans fats. Most fats that have a high percentage of saturated fat or that contain trans fat are solid at room temperature. Because of this, they’re typically referred to as solid fats. They include beef fat, pork fat, butter, shortening and stick margarine.
The study (Prolonged Intake of Dietary Lipids Alters Membrane Structure and T Cell Responses in LDLr-/- Mice) focused on the influence of saturated fats on a type of immune cells—T lymphocytes, or T cells, which play a major role in the adaptive immune response. To determine how a diet rich in saturated fats impacts immune function, researchers fed mice a Western-style, high-fat diet for nine weeks and examined how this diet impacts the T cell response. The study results show that dietary lipids directly influence T cell activation and responsiveness by altering the composition and the structure of the T cell membrane. These effects are present prior to the occurrence of weight gain and other clinical signs of obesity.
Abigail Pollock, lead author of the study, said in a press release that excess body fat can cause severe health problems. “Obesity is now a huge financial burden to the health systems of many Western countries. The World Health Organization reported in 2014 that more than 1.9 billion adults were overweight, and of these over 600 million were obese.” She added: “But what if immune dysfunction occurs before obesity? Our research looked at whether bad diets have consequences before we notice an increase in body weight. And we found that the over consumption of saturated fats is a form of malnutrition: one that needs to be taken seriously.”
The study results were surprising—although the researchers hypothesized that the T cell response would be weakened, they actually saw the opposite. The percentage of proliferating T cells increased. The researchers found that when mice consume greater amounts of saturated dietary lipids, the percentage of cholesterol within the cell decreases and the percentage of phospholipids increases, which induced a subtle change in the membrane composition. This membrane-related change result in noticeable effects on receptor signalling and T cell activation and proliferation in absence of a pro-inflammatory response.
Dr. Pollock said: “Lipids in the diet change the abundance of lipids in the cell membrane, which in turn changes the structure of the cell altering the responsiveness of the T cells and changing the immune response.” Kat Gaus, senior author of the study, added: “We now know that dietary lipids have the ability to directly affect T cell function through changing the lipid composition of the cell. Further research is needed to work out the link between lipids and T cell function so that we better understand which fats we should avoid.”