Results from a doctoral thesis from the Sahlgrenska Academy at the University of Gothenburg, Sweden, indicate that Staphylococus aureus-induced mortality is associated with dietary fat consisting of saturated and monounsaturated fatty acids, but not polyunsaturated fatty acids. The doctoral student, Louise Strandberg, also investigated different variants of three genes that are important for the immune system and noted that several of the gene variants that strengthen immunity also result in less obesity.
The research was conducted on mice. Strandberg said that S. aureus-induced mortality was investigated in four groups where subjects were fed: a lard-based high fat diet (HFD), a diet rich in saturated and monounsaturated fatty acids (HFD/S), a low fat diet (LFD) or a HFD rich in polyunsaturated fatty acids (HFD/P) from fish. After eight weeks on these diets the mice were exposed to S. aureus intravenously.
The results showed that the obese HFD/S-fed mice had increased S. aureus induced mortality compared with the lean LFD-fed mice. The HFD/S-fed mice showed signs of immune suppression evidenced by increased bacterial load and decreased capacity to phagocytose bacteria. Additionally, the HFD/P-fed mice displayed a degree of obesity and glucose intolerance that was milder than in the HFD/S-fed mice, but higher than in LFD mice.
Interestingly, the S. aureus induced mortality and the bacterial load of HFD/P-fed mice were comparable with that of LFD-fed mice, and markedly lower than that of mice fed HFD/S. This suggests that fatty food rather than obesity in itself affected the ability of the mice to fight off sepsis caused by bacteria. The usual assumption is that obesity itself is associated with inflammation that does not result from an infection, meaning that the immune defences are activated unnecessarily. Ironically, the mice on the high-fat diet (HFD/S) seem to have a less active immune system when it is really needed.
Strandberg concluded that the white blood cells of the mice on the HFD/S diet got worse at dealing with bacteria in the blood which could have contributed to many of them dying of sepsis. There are some quite interesting findings in this doctoral research that are well worth follow-up study.
Tags: dietary fats, immunity