Elsevier

Clinical Nutrition

Volume 38, Issue 4, August 2019, Pages 1672-1677
Clinical Nutrition

Original article
Higher adherence to plant-based diets are associated with lower likelihood of fatty liver

https://doi.org/10.1016/j.clnu.2018.08.010Get rights and content

Highlights

  • We examined the association of the overall plant-based diet (PDI), hypothesized healthful PDI (hPDI) and unhealthful PDI (uPDI) with non-alcoholic fatty liver disease (NAFLD) in US adults.

  • Liver function tests including alanine aminotransferase (ALT), aspartate aminotransferase (AST) and fatty liver index (FLI) decreased across increasing thirds of PDI and hPDI (all p < 0.001). There was reverse trend for the adjusted mean of ALT, AST and FLI across increasing thirds of uPDI.

  • After adjustment, participants in the upper third of PDI had 21% lower odd of NAFLD compared with those in the first third [odds ratio (OR): 0.79, 95% confidence interval (95%CI): 0.74–0.82]. A similar trend was observed with hPDI; and the opposite across increasing thirds of uPDI.

Summary

Some plant-based diets have been suggested to have a beneficial impact on liver disease risk. We examined the association of the overall plant-based diet (PDI), hypothesized healthful PDI (hPDI) and unhealthful PDI (uPDI) with non-alcoholic fatty liver disease (NAFLD) in US adults from the 2005–2010 National Health and Nutrition Examination Survey (NHANES2005-2010). Analysis of covariance, linear and logistic regression models accounted for the survey design and sample weights. Overall, 18,345 participants were included, with a mean age of 47.9 years and comprising 51.7% women. Liver function tests including alanine aminotransferase (ALT), aspartate aminotransferase (AST) and fatty liver index (FLI) decreased across increasing thirds of PDI and hPDI (all p < 0.001), while adjusted mean of ALT, AST and FLI increased across increasing thirds of uPDI. Adjusted linear regressions showed that PDI and hPDI had negative and significant associations with ALT (PDI = β:-0.095, hPDI = β:-0.128), AST (PDI = β:-0.101, hPDI = β:-0.138) and FLI (PDI = β:-0.153, hPDI = β:-0.265), while uPDI had a positive and significant association with ALT (β: 0.103), AST (β: 0.112) and FLI (β: 0.241). After adjustment, participants in the upper third of PDI had 21% lower odd of NAFLD compared with those in the lowest third [odds ratio (OR): 0.79, 95% confidence interval (95%CI): 0.74–0.82]. A similar trend was observed with hPDI; and the opposite across increasing thirds of uPDI. Our findings confirm that healthy plant-based diets are associated with lower NAFLD risk and more favorable liver function tests profile.

Introduction

Non-alcoholic fatty liver disease (NAFLD), a condition that occurs with the accumulation of triglycerides in the hepatic cells, is a rapidly growing health problem [1]. Between 20 and 46% of the adults in Western countries have NAFLD [2], [3]; while a quarter to nearly all people in some segments of the population including obese, and people with diabetes have NALFD [4]. Complex mechanisms including fat accumulation, insulin resistance, and inflammation have been suggested to be involved in the pathogenesis of NAFLD [5]. During the progression of the disease, reactive oxygen species (ROS) are activated and as such induce oxidative stress (OS) [6]. Intrahepatic antioxidants such as glutathione, vitamin E, β-carotene, and vitamin C inactivate these ROS in order to prevent such oxidative stress [7], [8].

Diet is the main driver of hepatic triglycerides accumulation [9], and could play a crucial role in the anti-oxidant capacity of the liver and entire body. Vegetarian diets are antioxidants rich and main sources of anti-inflammatory phytochemicals which may reduce oxidative stress [10], [11] and protect against different types of free radicals, and accordingly protect against NAFLD [10], [11]. However, there is still a lack of agreement on the dietary composition that fuels the development of NAFLD. There have been reports that a diet comprising more carbohydrates and less fat, but same amounts of protein and energy, was linked with a higher severity of NAFLD [9], or that NAFLD subjects had a greater intake of saturated fatty acids compared with healthy subjects [12]. Few studies have also investigated the effect of dietary pattern on liver. A population-based study in Germany has indicated that dietary pattern associated with a fatty liver was characterized by lower intakes of tea, confectionary, fats, bread, breakfast cereals and cheese and higher intakes of soups, beer, wine, juice, poultry and eggs [13]. Among 999 Chinese adults, the highest quarter of grains–vegetables dietary pattern was associated with the lowest prevalence of NAFLD [14]. However, there is still much to investigate regarding the quality of the diet and pattern significantly associated with reduced risk of NAFLD [15]. Several studies have suggested a beneficial role of plant-based diets on several diseases [16], [17], [18]. However, there is controversy among existing studies [10], [19]. For example, in a cross-sectional study of 615 Buddhists, vegetarian diet was not protective against NAFLD [19]. In another cross-sectional study in a Chinese population, Vegetarian diets were associated with lower odds of fatty liver [20]. Existing studies also have some limitations including the definition of plant-based diets as “vegetarian” diets, and dichotomization of study participants into those who do or do not consume some or all animal foods [21], [22]. Moreover, previous studies did not differentiate between refined grains and potatoes, and other components of a vegetarian diet as these foods are associated with adverse cardio-metabolic risk factor profile including insulin resistance, with a cofactor of NAFLD [23], [24], [25].

Continuous scoring system has been suggested as more refined approach for assessing plan-based diets. In this approach as implemented for instance by Martínez-González et al. [16], plant foods are assigned a positive load and animal food assigned negative points. Then an overall plant-based diet index (PDI) is derived to capture the consumption of all plant foods while reducing animal foods intake, a healthy plant-based diet index (hPDI) used to describe the intake of healthy plant foods associated with improved health outcomes such as whole grains, fruits and vegetables; and lastly an unhealthy plant-based diet index (uPDI) used to characterize the consumption of less healthy plant foods known to be associated with a higher risk of several diseases [26].

In the current study, we aimed to evaluate the impact of PDI, hPDI and uPDI on likelihood of NAFLD and liver function tests in a large, nationally representative sample of US adults.

Section snippets

Study population

This was a cross-sectional study using data from the US National Health and Nutrition Examination Survey (NHANES). The National Center for Health Statistics (NCHS) Research Ethics Review Board approved the underlying protocol and written informed consent was obtained from all participants. The current study was based on the analysis of data for two 2-year NHANES survey cycles between 2005 and 2010, restricted to participants aged ≥18 years. Details on NHANES Laboratory/Medical Technologists

Results

Overall, 18,345 participants were included, with a mean age of 47.9 years and comprising 51.7% women. The demographic characteristics of the participants according to PDI, hPDI and uPDI are shown in Table 1. Participants with higher scores on PDI or hPDI were older and leaner, and also had higher education, lower score of poverty-to-income, and were less likely to smoke than participants with lower scores (p < 0.001 for all comparisons). Conversely, high consumers of uPDI were younger, less

Discussion

In this large cross-sectional investigation conducted in a well-characterized nationally representative sample of adult Americans, a higher adherence to PDI and hPDI were inversely associated with likelihood of NAFLD, while there was a positive link between diet with higher score of uPDI and chance of NAFLD. Participants with higher adherence to PDI and hPDI had better profile of liver function tests, whilst the reverse [worst] was observed for uPDI. These relationships were independent of

Conclusions

Our findings shed light on the inverse link between healthy plant-based diets and likelihood of NAFLD and more favorable liver function tests; conversely we have found that unhealthy plant diet would have adverse impact on the liver function tests and higher chance of NAFLD. Dietary guidelines and lifestyle interventions could recommend increasing intake of healthy plant foods, while reducing the consumption of less healthy plant and certain animal foods. The present study supports current

Financial disclosure

None.

Conflicts of interest

None for all co-authors.

Acknowledgments

None.

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