Fructose is the major carbohydrate present in fruit.
Although some dietary fructose is derived from fruit, much fructose consumed in the diet is derived from sucrose (commonly known as ‘sugar’) and from foods containing added sucrose.
In a new study, researchers found high levels of fructose in the diet inhibit the liver’s ability to properly metabolize fat.
This effect is specific to fructose. Indeed, equally high levels of glucose in the diet actually improve the fat-burning function of the liver.
This explains why high dietary fructose has more negative health impacts than glucose does, even though they have the same caloric content.
The research was conducted by a team at Joslin Diabetes Center.
This is one of a series of studies that the team has been doing concerning what role high fructose in the diet plays in terms of insulin resistance and metabolic syndrome.
The team compared effects on metabolism of six different diets: regular chow, chow with high fructose, chow with high glucose, a high-fat diet, a high-fat diet with high fructose, and a high-fat diet with high glucose.
They analyzed different known markers of fatty liver to determine the effects of each diet.
They found fructose makes the liver accumulate fat. It acts almost like adding more fat to the diet.
This contrasts the effect of adding more glucose to the diet, which promotes the liver’s ability to burn fat, and therefore actually makes for a healthier metabolism.
The team says the most important takeaway of this study is that high fructose in the diet is bad.
It’s not bad because it’s more calories, but because it has effects on liver metabolism to make it worse at burning fat.
As a result, adding fructose to the diet makes the liver store more fat, and this is bad for the liver and bad for whole body metabolism.
When people switch the sugar in the diet from fructose to glucose, even though they’re both equally caloric, the glucose doesn’t have that effect.
In fact, if anything, overall metabolism is somewhat better than if they just were on plain high-fat diet.
The lead author of the study is C. Ronald Kahn, Chief Academic Officer at Joslin and the Mary K. Iacocca Professor of Medicine, Harvard Medical School.
The study is published in Cell Metabolism.
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