Fructose may be more damaging to your health than glucose according to a rigorous new animal study comparing the effect of both sweetening compounds on liver metabolism. The research presents some of the clearest causal evidence to date demonstrating how a high-fructose diet not only disrupts the liver’s ability to metabolize fat but also fundamentally damages its mitochondria.
“This is one of a series of studies that we've been doing concerning what role high fructose in the diet plays in terms of insulin resistance and metabolic syndrome,” explains C. Ronald Kahn, lead author on the study. “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.”
Previous research had identified this discordancy between the metabolic effects of glucose versus fructose on the liver, but exactly what was going on mechanistically was unclear. To home in on the physiological processes at play, the researchers compared the metabolic effects of six different diets in mice, including regular and high-fat diets with either high-fructose or high-glucose additions.
A number of different metabolic markers quickly stood out to the researchers. A high-fat, high-fructose diet increased levels of molecules called acylcarnitines in liver cells. This suggested there were excess fat burning processes occurring in the liver of the animals eating this diet in particular.
Another red flag identified by the researchers in relation to the high-fat, high-fructose diet was low levels of an enzyme called CPT1a. Low levels of this enzyme suggested high-fructose diets seemed to be damaging certain mitochondria responsible for normal fat burning processes. And looking more closely at the mitochondria specifically, the researchers discovered both high-fat and high-fat plus fructose diets were damaging these vital organelles.
“When mitochondria are healthy, they have this nice ovoid shape and crosshatching,” says Kahn. “In the high-fat plus fructose group, these mitochondria are fragmented and they're not able to burn fat as well as the healthy mitochondria. But looking at the high-fat diet plus glucose group, those mitochondria become more normal looking because they are burning fat normally.”
While none of this research goes to suggest high-glucose diets are safe or healthy, it is somewhat clear that despite equal caloric content, these metabolic abnormalities were not detected in high-glucose diets. So essentially, excess calories from a high-fat diet will be burned off more effectively when consumed with glucose instead of fructose. Fructose seems to help the liver not burn fat but synthesize and store it.
“The most important takeaway of this study is that high fructose in the diet is bad,” says Kahn. “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.”
The new research was published in the journal Cell Metabolism.
Source: Joslin Diabetes Center
