Nonalcoholic fatty liver disease (NAFLD) is a condition characterized by excess fat accumulation in the liver of individuals who drink little to no alcohol. It is one of the most common liver diseases worldwide, affecting up to 30% of the general population in Western countries.
NAFLD encompasses a spectrum of disease, ranging from simple steatosis (fatty liver), to nonalcoholic steatohepatitis (NASH), progressive fibrosis, cirrhosis, and even hepatocellular carcinoma. With rising rates of obesity, NAFLD is poised to become the leading cause of end-stage liver disease and indication for liver transplantation in the coming decades. Therefore, there is an urgent need to identify effective therapies to prevent and treat this condition.
Intermittent fasting (IF) has recently emerged as a promising lifestyle intervention for NAFLD. It involves cycling between periods of fasting and eating, rather than continuous calorie restriction. Studies in rodents and small trials in humans suggest IF may improve insulin sensitivity, reduce visceral fat, decrease inflammation, and prevent progression of NAFLD. This article will provide an overview of the potential mechanisms and clinical evidence supporting the use of IF as a treatment for NAFLD.
Mechanisms of Intermittent Fasting in NAFLD
Although clinical research is still early, proposed mechanisms help explain how IF may improve NAFLD.
Improved Insulin Sensitivity
Insulin resistance is nearly universal in patients with NAFLD and underlies disordered metabolism. During feeding, particularly of carbohydrate- and sugar-rich foods, insulin levels rise to promote glucose uptake, fat storage, and suppress fat breakdown. In obesity and NAFLD, tissues become resistant to insulin.
IF may help reverse insulin resistance through periods of low insulin levels and using up stored liver glycogen. As liver glycogen becomes depleted after 12-14 hours of fasting, lipolysis increases and ketogenesis provides an alternative fuel source. Transitioning between fed and fasted states may resensitize the body to insulin and curb excess lipogenesis when eating resumes.
Reduced Visceral Adiposity
Excess visceral fat (ie around abdominal organs) promotes insulin resistance, inflammation, and fatty acid flux to the liver that worsens NAFLD. IF regimens, even without overall calorie reduction, have been shown to reduce visceral fat mass more than daily calorie restriction in both human and animal studies.
Fasting elicits lipolysis of triglycerides stored in visceral fat, releasing fatty acids into circulation for use as fuel by other tissues. Decreasing visceral adiposity through IF may therefore mitigate several drivers of NAFLD progression.
Anti-Inflammatory Effects
Inflammation is another key mechanism in NASH and fibrosis development [10]. Animal studies indicate fasting leads to reduced markers of inflammation and oxidative stress [11]. Potential anti-inflammatory effects may be mediated by decreased adiposity, improved insulin sensitivity, ketone production, and rest allowed for gut tissues. Though human data are lacking, this represents another pathway by which IF could improve NAFLD.
Other Protective Mechanisms
Further proposed benefits of fasting include allowing cellular repair processes during the fasting period, decreased muscle protein breakdown, and positive impacts on the gut microbiome. How these mechanisms factor into potential NAFLD benefits is still unclear.
Evidence for IF in Human NAFLD
Despite great interest in IF for NAFLD, few human clinical trials have been conducted so far. Several small studies have examined various IF regimens:
- Time-restricted feeding: 4-10 hours of daily eating window
- 5:2 diet: 5 days normal calorie intake, 2 days fasting/restricted calories
- Alternate day fasting: fasting every other day
In general, IF regimens appear safe and effective for weight loss in NAFLD patients, resulting in reductions in liver fat on imaging [13]. However, most trials were short-term and lacked control groups.
A 2019 randomized trial compared the effects of three IF regimens to standard daily calorie restriction in NAFLD patients over 1 month. The time-restricted feeding group had the greatest reduction in MRI-measured liver fat, more than the daily calorie reduction group. However, there were no differences between groups in liver stiffness, a measure of fibrosis.
Overall, IF shows promise for improving steatosis, but longer-term, larger trials are needed to clarify optimal regimens and effects on NASH and fibrosis. Ongoing trials continue to evaluate IF in NAFLD populations.
Implementing Intermittent Fasting in Patients
Some tips on starting IF with patients in clinical practice:
- Assess patient preferences – some may prefer fasting, others changing diet
- Gradually increase fasting periods over weeks from 12 to 16+ hours
- Allow beverages like water, coffee, tea during fasts
- Ensure medical supervision for prolonged fasting >24 hrs
- Monitor for side effects like hunger, headaches, irritability
Education on possible benefits, close monitoring, and a gradual approach are key for adherence and safety. IF may be a useful option for motivated patients looking to target multiple metabolic risk factors underlying their NAFLD.
Intermittent Fasting Is an Emerging Intervention
In conclusion, intermittent fasting is an emerging intervention that may confer benefits for patients with NAFLD. Proposed mechanisms like improved insulin sensitivity, reduced inflammation, and decreasing visceral fat could slow or prevent progression of liver disease.
Early clinical studies support IF as a safe, effective strategy for reducing steatosis, however long-term, randomized controlled trials are still needed. With further research, IF could provide a cost-effective lifestyle approach to managing this extremely prevalent condition.
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