Added sugars in diet can cause fat accumulation in liver

Dear Doctor: Can you explain that study that says having too much sugar in your diet is going to make your body produce more fat? I always thought that the reason you gained weight was that you were eating too many calories.

Dear Reader: We believe you’re referring to a study published in the Journal of Hepatology in March. (Hepatology is the study of the liver, gallbladder and pancreas.) Because it focused on the ever-fascinating topic of the health effects of added sugar in the diet, the results received a fair bit of media attention.

You mentioned calories and weight gain, but that wasn’t the specific focus of this study. Rather, researchers in Zurich wanted to learn how sugar consumption affects the accumulation of fat in the liver. This may sound obscure, but due to a potentially serious condition known as fatty liver disease, it’s an important area of inquiry.

A healthy liver contains fat in small amounts. When fat begins to build up, though, it can cause inflammation. This, in turn, can lead to liver damage. One form of this condition, known as alcoholic fatty liver disease, is associated with heavy drinking. When fat accumulates in the livers of people who don’t drink heavily, it’s known as nonalcoholic fatty liver disease. It’s estimated that 25% of people in the United States, including children, have some degree of nonalcoholic fatty liver disease. For most, the condition doesn’t cause noticeable problems. But for up to one-third of them, the condition can progress and affect liver function.

Risk factors for nonalcoholic fatty liver disease include obesity, particularly when high levels of belly fat are present; insulin resistance; diabetes; elevated blood pressure; sleep apnea; and high blood lipid levels. And now, this new study suggests that certain types of added sugars can also play a role.

Elizabeth Ko, MD and Eve Glazier, MD

The researchers had 94 healthy men add a beverage sweetened with 80 grams of one of three different types of sugar to their regular diet. That’s the equivalent of two cans of soda. Using radioactive tracers, they monitored the effect on levels of liver fat during the seven weeks of the study. No changes to fat accumulation were seen in the men drinking glucose, which is the simple sugar our bodies produce and use for energy. But the group whose drinks were sweetened with sucrose or with a liquid form of fructose had double the fat accumulation of the glucose group. This effect continued for 12 hours after their last sweetened drink. The takeaway is that the added sugars we find in so many of our foods may be adversely affecting us, often in ways we can’t see or feel, and causing harm.

The American Heart Association recommends that women and men limit sugar intake to 25 and 48 grams per day, respectively. That’s about 6 teaspoons for women and about 9 for men. Sugar is so easily and widely available, it can be hard to avoid. But emerging research continues to show that, for your long-term health and well-being, it's an important step to take.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)


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