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Certain types of sugar may cause the liver to produce too much fat, a new study shows. Clara Bayo/EyeEm/Getty Images
  • Consuming moderate amounts of specific types of sugar may double the production of fat in the liver.
  • This in turn can lead to the development of fatty liver disease and type 2 diabetes.
  • A recent study found that sucrose boosted fat synthesis slightly more than the same amount of fructose.

New research provides further evidence of the dangers of consuming sugar, proposing that ingesting even moderate amounts of the substance may lead to a change in a person’s metabolism.

Researchers at the Medical University of Graz, Austria, and the University of Zurich and the University Hospital Zurich, Switzerland, recently reported their findings in theJournal of Hepatology.

Some sugars are natural components of fruits and vegetables. However, many of the processed foods we eat contain added sugars — sugar that the manufacturers add to foods and beverages to enhance their flavor or improve food’s appearance and texture.

High sugar intake has been linked to numerous health problems, including type 2 diabetes, obesity, cardiovascular disease, and cancer.

In 2015, the World Health Organization (WHO) advised that people eat no more than 5% of their daily calories from added sugar. For a diet of 2,000 calories per day, this would amount to 100 calories or 6 teaspoons or roughly 25 grams (g) of added sugar.

In 2015, market research firm Euromonitor reported that the average person in the United States consumes more than 126 g of sugar per day.

Meanwhile, the average person in the United Kingdom consumed 93.2 g.

Switzerland did not make the list of the top 10 countries whose citizens consume the most sugar. Still, the average person there consumed 76.1 g per day in 2015.

Authors of the study were interested in finding out what happens when people consume moderate amounts of added sugar.

For their work, which they carried out between 2013 and 2016, they recruited 94 healthy male volunteers. The participants were aged 18–30 years and had a body mass index under 24kg/m2, which is considered a moderate weight.

The researchers selected participants under a certain weight to decrease the odds of recruiting people who had possibly already developed increased liver fat content.

Males who already consumed sugar-sweetened beverages daily or who logged more than 3 hours of physical activity per week were also excluded.

The researchers explained they did not study females, “as there is evidence for divergent metabolic effects of fructose on male and female subjects.”

Indeed, a 2008 study reported that fructose caused “markedly blunted” metabolic effects on young female participants compared with male ones.

The researchers initially had the participants abstain from sugar-sweetened beverages for 4 weeks. The participants then started drinking sugar-sweetened drinks containing either fructose, sucrose, or glucose three times per day. A total of 80 g of each type of sugar was consumed daily.

A fourth group of participants were asked to continue sugar-sweetened beverage abstinence.

To examine how drinks with added sugar affected the individuals, the researchers used tracers, which are substances that can be followed as they move through the body.

Overall, the researchers found the participants did not consume more calories than they did before the study. The authors hypothesize that having sugary drinks increased the participants’ satiety, causing them to eat fewer calories from other sources.

The researchers also reported that even though the participants consumed the same number of calories, adding sugar-sweetened drinks to their diets impacted their overall health.

The participants who drank beverages sweetened with fructose had fat production twice as high as those who drank beverages sweetened with glucose and those who abstained from sugar-sweetened drinks.

“This was still the case more than 12 hours after the last meal or sugar consumption,” says study leader Dr. Philipp Gerber of the Department of Endocrinology, Diabetology, and Clinical Nutrition at the University of Zurich.

Fat building up in the liver leads to serious health issues, such as type 2 diabetes and nonalcoholic fatty liver disease.

A particularly surprising finding by the researchers was that sucrose, or table sugar — the form of sugar humans most commonly consume — boosted fat synthesis slightly more than the same amount of fructose. Until now, most scientists believed fructose to be more likely to cause such changes.

Dr. Gerber notes that the typical Swiss does not follow the WHO advice to limit their daily sugar consumption to 25 g. “Our results are a critical step in researching the harmful effects of added sugars and will be very significant for future dietary recommendations,” he says.

The scientists also note some limitations to their research.

They say that they had “little control” over the participants’ compliance in the study and that they did not know their “intestinal capacity.” In other words, not knowing the participants’ individual tolerability of fructose may have led to variation in the results.