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


  • 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
  • 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.