How improving diet quality reduces premature death risk

*Chronic liver inflammation linked to Western diet

People who improve the quality of their diets over time, eating more whole grains, vegetables, fruits, nuts, and fish and less red and processed meats and sugary beverages, may significantly reduce their risk of premature death, according to a new study from Harvard T.H. Chan School of Public Health, United States (U.S.). It is the first study to show that improving diet quality over at least a dozen years is associated with lower total and cardiovascular mortality, and underscores the importance of maintaining healthy eating patterns over the long term.

The study will be published in the New England Journal of Medicine.”Overall, our findings underscore the benefits of healthy eating patterns including the Mediterranean diet and the DASH diet. Our study indicates that even modest improvements in diet quality could meaningfully influence mortality risk and conversely, worsening diet quality may increase the risk,” said lead author Mercedes Sotos-Prieto, who worked on the study while a postdoctoral fellow in the Harvard Chan School Department of Nutrition and who is currently an assistant professor of nutrition at Ohio University.

Sotos-Prieto and colleagues analyzed the association between changes in diet quality among nearly 74,000 adults over a 12-year period (1986-1998) and their risk of dying over the subsequent 12 years (1998-2010). Data came from two long-term studies, the Nurses’ Health Study and the Health Professionals’ Follow-up Study, in which participants answered questions about their diets every four years and about their lifestyle and health every two years. The researchers assessed people’s diet quality by using three different scoring methods: the 2010 Alternate Healthy Eating Index, the Alternate Mediterranean Diet score, and the Dietary Approaches to Stop Hypertension (DASH) diet score. Each of these methods assigns scores to various types of food or nutrients; less healthy foods or nutrients have lower scores and healthier foods or nutrients have higher ones. The study found that improved diet quality over a 12-year period was associated with reduced risk of death in the subsequent 12 years, no matter which score was used. Food groups that contributed most to an improvement in diet quality were whole grains, fruits, vegetables, and fish or n-3 fatty acids.

A 20-percentile increase in diet-quality scores – the kind of increase that can be achieved by swapping out just one serving of red or processed meat for one daily serving of nuts or legumes – was linked with an eight per cent-17 per cent reduction in the risk of death, depending on the diet score. In contrast, worsening diet quality was associated with a six per cent-12 per cent increase in the risk.

Also, a new study in The American Journal of Pathology reports that mice fed a Western diet, which is high in fat and sugar, resulted in hepatic inflammation, especially in males. Moreover, liver inflammation was most pronounced in Western diet-fed male mice that also lacked farnesoid x receptor (FXR), a bile acid receptor.

The study is important because it links diet to changes in the gut microbiota as well as bile acid profile, opening the possibility that probiotics and bile acid receptor agonists may be useful for the prevention and treatment of hepatic inflammation and progression into advanced liver diseases such as cancer. Other published data have already shown that FXR-deficient mice spontaneously develop steatohepatitis and liver tumors even when they are fed a normal rodent diet. In this study, wild-type and FXR-deficient mice were fed either a Western diet or a matching control diet for 10 months. They found similarities between Western diet intake and FXR deficiency.

For instance, both Western diet-fed wild-type mice and control diet-fed FXR KO mice developed steatosis, which also was more severe in males than females. Interestingly, however, only the FXR-deficient male mice had massive lymphocyte and neutrophil infiltration in the liver, and only Western diet-fed male FXR KO mice had fatty adenomas.