(CSEMP010) LONG-TERM EXPOSURE TO KETOGENIC DIET INDUCES NAFLD IN APOE DEFICIENT MICE: A ROLE FOR GUT MICROBIOTA ALTERATIONS AND TOLL-LIKE RECEPTOR 5

Background: With the rising prevalence of obesity worldwide, there has been a paradigm shift in how we view dietary fats, particularly after reintroducing ketogenic diet (KD) as a quick weight loss strategy. Interestingly, among the top-10 best-selling weight loss books on Amazon.com in 2022, four books promote KD. However, numerous epidemiological studies have reported that a higher dietary intake of fat increases the risk for nonalcoholic fatty liver disease (NAFLD) regardless of body weight. Hence, the objective of this study is to explore the long-term effects of KD on NAFLD in mice.

METHODS AND RESULTS: 6-week-old apolipoprotein E-deficient (ApoE-/-) male mice were fed either a low-fat diet (LFD), high-fat diet (HFD) or KD for 12 weeks. During this study, glycemic control was monitored in mice via glucose and insulin tolerance testing, whereas hepatic fat accumulation was assessed using histological staining and biochemical analysis.

Results: Despite consuming a high-energy-dense diet, KD-fed mice maintained a normal body weight pattern that matched that of lean mice and had higher circulating ketone levels than the other groups. In addition, KD-fed mice showed reduced random blood glucose levels, especially during the first half of the study, which were similar to those observed in the LFD group. However, these effects were not sustained, and glucose tolerance and insulin sensitivity worsened at 12 weeks post-diet. Although KD-fed mice exhibited lower circulating triglycerides (TG) and lipoprotein levels than obese mice, their liver appeared yellowish and had the highest levels of TG and cholesterol among the three groups. Furthermore, histological examination using hematoxylin and eosin (H&E) staining revealed that KD-fed mice developed NAFLD, characterized by a higher number of fat droplets compared to the HFD group. Notably, KD prompts NAFLD irrespective of increased gene expression of hepatic fatty acid oxidation and decreased de novo lipogenesis (DNL) compared to the HFD group. Finally, our data suggest that KD-induced NAFLD may be mediated by altering gut microbiota, as evidenced by the global increases in gene expression of toll-like receptor 5 (TLR5), a member of the TLR family that recognizes bacterial flagellin and linked to the development of NAFLD.

Conclusion: Our data suggest that long-term exposure to KD induces NAFLD by altering gut microbiota, thereby promoting TLR5 gene expression and aggravating NAFLD in ApoE-/- mice.