- Nonalcoholic fatty liver disease (NAFLD), characterized by the excessive accumulation of fat in the liver that is not caused by alcohol consumption, is the major cause of chronic liver disease.
- Individuals with obesity are at an increased risk of NAFLD, and weight loss can help reduce liver fat levels and improve NAFLD symptoms.
- A recent randomized clinical trial compared the effectiveness of time-restricted eating accompanied by reduced calorie intake and conventional daily calorie restriction in reducing liver fat levels in individuals with NAFLD.
- The study found that both time-restricted eating and daily calorie restriction resulted in a similar decline in liver fat content and other markers of liver dysfunction.
- These results suggest that reducing calorie intake could be more important than solely restricting food intake to a specific time window for the management of NAFLD.
Time-restricted eating involves limiting all food intake to a specific time window during the day. Some doctors regard it as a better strategy for long-term weight loss than simple calorie restriction due to better long-term adherence.
A recent randomized clinical trial published in JAMA Network Open shows that both calorie restrictions with or without time-restricted eating resulted in similar reductions in liver fat levels and improvements in metabolic markers.
These results underscore the importance of calorie restriction with time-restricted eating for the management of nonalcoholic fatty liver disease (NAFLD) and other metabolic disorders.
However, time-restricted eating improved insulin sensitivity to a greater extent than conventional calorie restriction.
Weight loss and NAFLD
NAFLD refers to a range of conditions involving the accumulation of fat in the liver not caused by excessive alcohol intake. The excess buildup of fat in the liver can lead to inflammation, liver damage, and fibrosis, which involves the formation of scar tissue in the liver.
Nearly one in four individuals across the globe have NAFLD, with those with obesity and metabolic disorders being at an increased risk of this condition.
Estimates suggest that between 50 to 90% of individuals with obesity have NAFLD. This is especially concerning given that NAFLD is the most common cause of chronic liver disease.
Lifestyle modifications, including diet and physical exercise, that lead to weight loss can help lower liver fat content and improve other symptoms associated with NAFLD
Calorie restriction involving consuming fewer calories daily to produce an energy deficit has been conventionally recommended for inducing weight loss. However, the daily calorie restriction can be difficult to sustain over a prolonged duration.
This has led to a surge in interest in time-restricted eating, a form of intermittent fasting, that limits food intake to a specific time window, ranging from 6 to 12 hours, during the day.
Why time-restricted eating?
Time-restricted eating does not require changing calorie intake as long as food intake is restricted to the time window, making it easier to adhere to this dietary pattern.
Besides facilitating weight loss, time-restricted eating can also help reduce blood pressure, improve blood glucose control, and reduce body fat mass.
Despite the lack of restriction on energy intake, time-restricted eating can also lead to a lower intake of calories. Studies in rodents suggest that several of the beneficial effects of time-restricted eating on metabolic health are due to the time of intake of food rather than a reduction in calorie intake.
However, whether the cardiometabolic benefits of time-restricted eating in humans are due to limiting food intake to the specific time window or due to the concomitant decline in caloric intake is not well understood.
In other words, unlike in rodents, calorie restriction and timing of meal consumption together may mediate some of the beneficial effects of time-restricted eating in humans.
Moreover, the evidence on the impact of time-restricted eating on liver fat content in individuals with NAFLD is mixed and has been obtained from short-term studies.
A recent randomized clinical trial conducted in China sought to identify whether the benefits of time-restricted eating in NAFLD were simply due to calorie restriction or if the timing of eating was also important.
What happened in the new study?
The aforementioned study enrolled 88 individuals aged between 18 and 75 years with obesity and NAFLD. These individuals were randomly assigned to follow a diet with either time-restricted eating and calorie restriction, or just calorie restriction for 12 months.
The individuals in the time-restricted eating group were asked to limit food intake between 8 a.m. and 4 p.m., whereas the daily calorie-restriction group participants had meals at their normal times.
The participants in both groups were instructed to limit their calorie intake, with men required to restrict calorie intake to between 1,500–1,800 kilocalories per day (kcal/day), and women asked to limit intake to 1,200–1,500 kcal/day.
The researchers used magnetic resonance imaging (MRI) to examine changes in intrahepatic triglyceride, or liver fat levels, between baseline and at 6 and 12 months after the initiation of the diet. In addition, they also measured liver enzymes and liver stiffness using an ultrasonic method called transient elastography.
Liver stiffness is caused by edema and fibrosis and is a marker of liver dysfunction. They also assessed body composition and cardiometabolic markers, such as blood glucose levels, blood pressure, and blood cholesterol levels, at baseline and then at 6 and 12 months.
Impact of diet on liver fat levels
Individuals in both time-restricted eating and daily calorie restriction group adhered to the diet for about 85% of days during the 12-month follow-up period.
Participants in both groups showed similar levels of reduction in liver fat levels at 6 and 12 months. Specifically, there was a 6.9% reduction in liver fat levels in participants in the time-restricted eating group and a 7.9% decline in individuals in the daily calorie restriction group at 12 months after diet initiation.
Moreover, the magnitude of change in liver stiffness and the percentage of individuals who achieved NAFLD resolution were similar in both groups.
The decline in body weight, changes in body fat levels, and improvements in glucose control, blood pressure, and metabolic markers, such as high-density lipoprotein and low-density lipoprotein cholesterol, were similar in both groups at 6 and 12 months.
The only difference observed between the two groups was the greater improvement in insulin sensitivity at 12 months in the time-restricted eating group compared with those practicing daily calorie restriction alone.
These results highlight the importance of reducing calorie intake while following a time-restricted eating pattern for the management of NAFLD symptoms.
Study limitations and implications
The researchers noted that they used noninvasive imaging techniques to assess liver fat content and liver stiffness instead of directly assessing these variables using liver biopsies.
However, they added that these noninvasive measures of liver fat levels and stiffness are strongly correlated with direct measures obtained using biopsies.
In addition, studies have shown that the specific time and frequency of food intake can influence the effectiveness of time-restricted eating, and these factors were not controlled for in the current study.
Dr. Hana Kahleova, director of clinical research at the Physicians Committee, not involved in this study, told Medical News Today:
“Eating breakfast, and making breakfast the largest meal of the day, have been shown to be independent factors in weight management. In the current study, the eating window between 8 a.m. and 4 p.m. enabled the study participants to consume a small breakfast — or completely skip breakfast — and consume most of the calories in the second half of the eating window, which may have lessened the benefits of this approach.”
“Furthermore, it has been shown that consuming larger meals results in a greater thermic effect of food, that is, a release of energy in the form of heat after consuming a meal, which is helpful for weight loss compared with consuming the same food in multiple small meals,” she noted.
“The current study did not instruct the participants to consume a few larger meals, and it is possible that the participants were eating multiple small meals throughout the eating window, which may have further limited the usefulness of this approach,” added Dr. Kahleova.
Yet the relative ease of adherence to a time-restricted eating pattern makes it an attractive strategy for NAFLD management.
“[E]ven with these limitations, the study demonstrated the beneficial effects of time-restricted eating on liver fat, body fat, and metabolic risk factors, which were, in this case, comparable to an energy-restricted diet without a time-restricted eating window,” Dr. Kahleova said.
According to her, “[t]ime-restricted eating is a simple approach that may help people with [NAFLD] limit their caloric intake and experience significant improvements in a relatively short period of time.”
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