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Fatty liver from fizzy drinks?

‘Two soft drinks a day may lead to long term liver damage’, The Daily Telegraph has reported. The newspaper said that a new study has found that, like the known risks that alcohol poses to the liver, fizzy drinks with a high sugar content can increase a person’s risk of developing fatty liver disease.

This small study looked at 60 patients with non-alcoholic fatty liver disease (NAFLD), comparing their soft-drink habits, dietary intake, and blood markers of inflammation and insulin resistance to 18 controls without liver disease. The study found much higher levels of soft-drink consumption in those with NAFLD compared to those without.

Obesity, high blood sugar, high blood pressure and high cholesterol are all features of metabolic syndrome, a condition associated with NAFLD. Therefore, it seems plausible that someone who consumes more sugary drinks may have other health behaviours and risk factors that contribute to NAFLD risk. Limitations in the study design and certain statistical adjustment methods mean that the work cannot prove that soft drinks alone are the cause of fatty liver. The full report of the research will be of interest when it is published later this year.

Where did the story come from?

This research was conducted by Nimer Assy and colleagues from The Liver Unit, Ziv Medical Center and other institutions in Israel. The short article was a poster presentation published in the Journal of Hepatology.

What kind of scientific study was this?

This was an observational study in which the researchers aimed to examine the association between soft-drink consumption and non-alcoholic fatty liver disease (NAFLD) in people with or without metabolic syndrome.

NAFLD is an increase in the fat in the liver in the absence of a history of excessive alcohol consumption. The condition increases risk of liver hepatitis and cirrhosis. Metabolic syndrome is a group of risk factors that increase the risk of heart disease and diabetes. These risk factors include high blood sugar, high blood pressure, abnormal lipids, such as high triglycerides, and abdominal obesity.

The study involved 60 patients with NAFLD, with an average age of 53 years: 32 patients with NAFLD and risk factors of diabetes, obesity or high triglycerides, and 28 patients who had NAFLD but no risk factors. The study also featured 18 control subjects without NAFLD, matched by age and gender.

The researchers performed ultrasound scans to look at the degree of fatty infiltration in the liver. They also carried out laboratory tests of the subjects’ resistance to insulin, inflammatory levels and markers of oxidant–antioxidant status.

The study had an observation period of six months, with the researchers collecting information on physical activity and administering a validated food questionnaire to record daily intake of food and soft drink at both the beginning and end of this period. The authors used this research to collect two seven-day records of added sugar intake.

What were the results of the study?

Of the 60 patients with NAFLD, 70% drank soft drinks excessively (>500ml/day or >12tsp/day of added sugar) compared to 20% of the 18 healthy controls.

The researchers looked at the soft-drink consumption of those with NAFLD. On most days of the six months 7% of those with NAFLD had one soft drink a day, 55% had two to three drinks a day and 38% drank more than four drinks a day. They report that the most common soft drinks consumed were classic Coca-Cola (53%), followed by flavoured fruit juices (47%).

The 29 patients with NAFLD and metabolic syndrome had similar inflammatory and oxidative stress markers compared to those with NAFLD without metabolic syndrome. However, tests found that those with metabolic syndrome had lower insulin sensitivity.

When the researchers adjusted their analysis to account for the influence of dietary intake and physical activity levels, they found that consuming multiple soft drinks increased the patients’ risk of fatty liver, regardless of whether they were diagnosed with metabolic syndrome or not.

What interpretations did the researchers draw from these results?

The authors report that patients with NAFLD have higher prevalence of soft-drink consumption, regardless of metabolic syndrome diagnosis. They suggest that this may allow for improved prediction of NAFLD risk and add insight to the role of sugary soft drinks as a cause of fatty liver.

What does the NHS Knowledge Service make of this study?

This small study looked at 60 patients with non-alcoholic fatty liver disease (NAFLD), with or without metabolic syndrome, and 18 controls without liver disease. It questioned their dietary intake and examined blood markers of inflammation and insulin resistance.

The study found much higher levels of soft-drink consumption in those with NAFLD compared to those without. Features of metabolic syndrome, such as being overweight or obese, having high blood sugar, high blood pressure, high cholesterol or triglycerides, are associated with NAFLD. Therefore, it seems plausible that someone who drinks higher amounts of sugary drinks may have other health behaviours and risk factors that contribute to risk of NAFLD. This study does not prove that soft drinks alone are the cause of fatty liver.

There are several points that must be considered when interpreting this research:

  • In this study the participants already had NAFLD when their soft-drink consumption was measured. It cannot prove that one preceded the other.
  • Although a food frequency questionnaire and details on physical activity were reported to have been gathered, no information is given in the article on the methods of collection, findings of the results or how the researchers adjusted their analysis to account for them.
  • In this assessment of soft-drink consumption, as with all food frequency questionnaires, there is the possibility of error through individuals’ estimation of amounts, different beverages consumed with different sugar levels (for example some may have been diet) and fluctuation of consumption levels over time.
  • Although all cases of fatty liver disease were reported to be non-alcoholic, we do not know whether alcohol consumption has actually been assessed in this report.
  • No information is provided on how study participants were recruited to the study. It is particularly important that the characteristics of the three groups are described in some detail, as there may be some differences in characteristics due to how they were selected rather than due to NAFLD.
  • With the small study size, particularly with only 18 control participants included, the observed differences in soft-drink consumption between the two groups may be chance findings. This could be different if a much larger sample were assessed.

As this study has so far been reported in brief summary format, the research community will be interested in reading it in full once it is published in a peer-reviewed journal.

Links to the headlines

DANGER OF JUST TWO FIZZY DRINKS. Daily Express, August 12 2009

Two soft drinks a day may lead to long term liver damage. The Daily Telegraph, August 12 2009

Links to the science

Abed A, Nseir W, Ali T et al. Soft drink consumption linked with fatty liver independently by metabolic syndrome. Journ of Hepat. April 2009

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