Prospective association between adherence to the Mediterranean diet and hepatic steatosis: the Swiss CoLaus cohort study.
BMJ Open 2020 ; 10: e040959.
PubMed ID : 33371031
PMCID : PMC7757450
The Mediterranean diet has been promoted as a healthy dietary pattern, but whether the Mediterranean diet may help to prevent hepatic steatosis is not clear. This study aimed to evaluate the prospective association between adherence to the Mediterranean diet and risk of hepatic steatosis.
Population-based prospective cohort study.
The Swiss CoLaus Study.
We evaluated 2288 adults (65.4% women, aged 55.8±10.0 years) without hepatic steatosis at first follow-up in 2009-2012. Adherence to the Mediterranean diet was scaled as the Mediterranean diet score (MDS) based on the Mediterranean diet pyramid ascertained with responses to Food Frequency Questionnaires.
New onset of hepatic steatosis was ascertained by two indices separately: the Fatty Liver Index (FLI, ≥60 points) and the non-alcoholic fatty liver disease (NAFLD) score (≥-0.640 points). Prospective associations between adherence to the Mediterranean diet and risk of hepatic steatosis were quantified using Poisson regression.
During a mean 5.3 years of follow-up, hepatic steatosis was ascertained in 153 (6.7%) participants by FLI criteria and in 208 (9.1%) by NAFLD score. After multivariable adjustment, higher adherence to MDS was associated with lower risk of hepatic steatosis based on FLI: risk ratio 0.84 (95% CI 0.73 to 0.96) per 1 SD of MDS; 0.85 (0.73 to 0.99) adjusted for BMI; and 0.85 (0.71 to 1.02) adjusted for both BMI and waist circumference. When using NAFLD score, no significant association was found between MDS and risk of hepatic steatosis (0.95 (0.83 to 1.09)).
A potential role of the Mediterranean diet in the prevention of hepatic steatosis is suggested by the inverse association observed between adherence to the Mediterranean diet and incidence of hepatic steatosis based on the FLI. The inconsistency of this association when hepatic steatosis was assessed by NAFLD score points to the need for accurate population-level assessment of fatty liver and its physiological markers.
Researchers from the MRC Epidemiology Unit, Cambridge, U.K. and University of Lausanne, Switzerland teamed up and reported that eating a Mediterranean-style diet may lower the risk of developing fatty liver disease.
Fatty liver, defined as fat accumulation of more than 5% of liver volume, is common especially among obese and diabetic individuals. Fatty liver is the first stage for non-alcoholic fatty liver disease (NAFLD), which is a major cause of liver disease worldwide, and may also predispose to higher risk of cardiovascular diseases. Thus it is important to find strategies that can prevent a fatty liver from developing in the first place.
The Mediterranean diet has been suggested as a potential strategy but past research was limited to people with established fatty liver disease with only sparse understanding about its role in prevention.
We conducted research in 2288 Swiss CoLaus study participants without existing NAFLD at baseline, when we assessed their dietary habits and scaled their levels of adherence to the well-established Mediterranean diet. After an average of 5.3-years of follow-up in the study, we tested for the presence of fatty liver disease based on two indices called “fatty liver index” and “NAFLD score” which use different combinations of information on the body status with respect to levels of obesity or thinness, blood fats, blood markers of liver function or the presence of metabolic disturbances or type 2 diabetes. Our results showed that those who adhered more to the Mediterranean diet had lower risk of developing new-onset fatty liver disease based on fatty liver index.
As with all research, there are some limitations of our work. For example, our estimates of fatty liver disease were based indirectly on markers that can signal fat accumulation, but not with direct imaging techniques such as by ultrasound or CT-scanning. Also, our research was able to observe what happened over time to participants, but there was no intervention with different levels of sticking to a Mediterranean-diet such as in a clinical trial, so no definite conclusions can be drawn about cause and effect.
This type of research with follow-up data after some years from the baseline has been conducted for the first time in a European population for a link between diet and liver fat accumulation. This serves as a good starting point for this important topic and should stimulate further research with more accurate measures of fatty liver.