Effect of a Low Free Sugar Diet vs Usual Diet on Nonalcoholic Fatty Liver Disease in Adolescent Boys: A Randomized Clinical Trial

JAMA. 2019;321(3):256-265. doi:10.1001/jama.2018.20579 —

Schwimmer JB, Ugalde-Nicalo P, Welsh JA, et al.

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  • To determine the effects of a diet low in free sugars in adolescent boys with NAFLD.


  • From 1988 to 2010, the prevalence of nonalcoholic fatty liver disease (NAFLD) increased among children in the United States.  Pediatric NAFLD is more common in boys than girls, and is now the most common liver disease in children.
  • Pediatric guidelines for the management of nonalcoholic fatty liver disease (NAFLD) recommend a healthy diet as treatment. Reduction of sugary foods and beverages is a plausible but unproven treatment.


  • A total of 40 adolescent boys, ages 11-16, were randomly assigned to either the intervention (low in free sugar) diet group or the usual diet group in a 1:1 ratio. For the intervention diet group, the target for free sugar intake was less than 3% of daily calories, in order to align with the current World Health Organization guidelines which recommend that daily free sugar intake is limited to less than 10% for all people and to less than 5% in specific circumstances.
  • The provided study diet was matched to the reported baseline diet except for sugar content, and the use of artificial sweeteners was prohibited.  Participants and their families were instructed not to purchase any food and to consume only the food provided by the study staff.
  • Study visits were conducted at baseline and at 4 and 8 weeks after initiation of the intervention. Demographic information, as well as medical history, vital signs, anthropometric assessments, and fasting blood collection for complete blood cell count, comprehensive metabolic panel, lipid panel, liver panel, prothrombin time, and international normalized ratio.
  • The Nutrition Data System for Research was used for the collection and analysis of 24-hour dietary recalls along with the analysis of food records, menus, and recipes. Evaluation of each participant’s diet was performed during the screening phase and between study weeks 3 to 8.
  • The primary outcome was change in percentage of hepatic steatosis measured by MRI-PDFF in the intervention diet group compared with change in the usual diet group over 8 weeks. 


  • The provision of a diet low in free sugars compared with usual diet resulted in a greater reduction in hepatic steatosis from 25% to 17% in the low free sugar diet group and from 21% to 20% in the usual diet group, a statistically significant difference of −6.23% when adjusted for baseline.
  • At week 8, mean levels of ALT, aspartate aminotransferase, and γ-glutamyl transpeptidasewere significantly lower in the intervention diet group compared with the usual diet group after adjusting for center and conditioning on baseline levels. The mean total cholesterol level changed from 162 to 147mg/dL in the intervention diet group and from 157 to 158 mg/dL in the usual diet group and there was a significant adjusted mean between-group difference of −15.16mg/dL.
  • There were no significant differences in glucose, insulin, homeostasis model assessment for insulin resistance, triglycerides, low-density lipoprotein cholesterol, or high-density lipoprotein cholesterol.


  • This study demonstrated that a significant improvement in hepatic steatosis could be achieved in adolescent boys with NAFLD by restricting dietary sugars over 8 weeks.
  • This clinical trial has shown that children and families can follow a diet low in free sugars for up to 8 weeks when the research team plans, purchases, and provides all meals. While this is not practical to generalize widely, it shows that a low sugar diet reduces biomarkers of NAFLD activity at least in the short term.

Points to Consider

  • In the present study, the sample included adolescent boys only, and the majority of the sample was Hispanic, thereby limiting the generalizability of the findings.
  • The intervention showed significant change, but did not achieve reduction of hepatic steatosis or ALT level into the normal range.  Liver biopsies were not included in this study and are needed to determine any changes in liver inflammation.
  • It is unclear if data on the types of sugar consumed at baseline and those consumes during the intervention were collected and compared within and between groups. Therefore, it is unclear whether any effect seen can be contributed to the amount of free sugar intake versus the type consumed.