In the past few years the evidence has been mounting that fructose can cause metabolic disturbance which may lead to development of metabolic syndrome.
A new study has added further weight behind this position, by suggesting that fructose can promote rapid liver damage in certain diets that are high in this sugar.
The study used 10 middle-aged, normal weight monkeys who were fructose naïve (never eaten fructose) and divided them into two groups based on comparable body shapes and waist circumference. Over six weeks, one group was fed a calorie-controlled diet consisting of 24 percent fructose, while the control group was fed a calorie-controlled diet with only a negligible amount of fructose, approximately 0.5 percent.
Each week during the study the research team weighed both groups and measured their waist circumference, then adjusted the amount of food provided to prevent weight gain. At the end of the study, the researchers measured biomarkers of liver damage through blood samples and examined what type of bacteria was in the intestine through faecal samples and intestinal biopsies.
In the high-fructose group, the researchers found that the type of intestinal bacteria hadn’t changed, but that they were migrating to the liver more rapidly and causing damage there. This is something that has been postulated in Nutrition circles for a while now, that there seems to be something about the high fructose levels that was causing the intestines to be less protective than normal (Intestinal Permeability AKA ‘Leaky Gut’), and consequently allowing the bacteria to leak out at a 30 percent higher rate.
There are, however, a few caveats that have to be taken into account. One is that, although the diets where similar in carbohydrate, protein and fat levels, which was part of the control methodology (to identify whether it was fructose alone, or in combination with caloric excess that was causing the issue), the sources providing these macronutrients where different, so this may have influenced the findings. The second caveat, which the authors also highlighted as a limitation of the study is that it only tested for fructose and not dextrose (glucose). Fructose and dextrose are simple sugars found naturally in plants, either individually or joined together as sucrose i.e. table sugar.
The Authors studied fructose because it is the most commonly added sugar in the American diet (where the study took place), but based on their findings can’t say conclusively that fructose caused the liver damage. They did suggest though that high added sugars caused bacteria to exit the intestines, go into the blood stream and damage the liver. They are planning a follow up study to tease apart this detail.
I will go out on a limb and suggest that the study will find that it ‘is’ the fructose that is causing the damage. Not because fructose is evil, but because it is doing what Nature intended it to do. The metabolic effects of fructose, if you look at them with the right ‘per-spectacles’ is a genius design, that probably kept us alive throughout our evolution. But when we took the fructose out of context for example by refining the sugar out of foods especially when we are using crops that we have purposely produced to have a higher proportion of fructose i.e. High Fructose Corn Syrup, then rather than a health promoting nutrient, we have a disease causing agent.
I’ll keep you posted on the results of the study, if, and when it takes place
Reference:
Kavanagh, K et al. Dietary fructose induces endotoxemia and hepatic injury in calorically controlled primates. Am J Clin Nutr August 2013, doi: 10.3945/ajcn.112.057331
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