Why carbs can turn your liver into foie gras

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It’s funny how things seem to come in threes, and this week was an example of this maxim in that I saw three patients all of whom had deranged liver function tests. All of them had raised levels of at least two liver ‘enzymes’. This, in medicine, is generally taken as a sign of damage to the liver. While there are lots of reasons for why liver enzymes may be raised, our first thought in medicine is usually to ask about alcohol consumption. None of these individuals was abstemious, but at the same time none of them had alcohol consumptions that could be described as excessive.

When I see individuals with deranged liver function who do not drink much alcohol, my next thought is usually their diet. And in particular, I start thinking about whether they may have a touch of ‘metabolic syndrome’. This condition, characterised by excess weight around the middle of the body, is common, and tends to be a sign of an excess of carbohydrate and therefore insulin in the body. Insulin promotes fatty production in the body, and some of this can end up being dumped in the liver. As a result, liver function can become deranged, and if the problem persists, it may eventually lead to a condition known as ‘fatty liver’.

As it happens, each of the three patients I saw this week were carrying excess weight around their middles. My advice to them was to get control over blood sugar and insulin levels. Basically, that means eating less carb, particularly those carbs that tend to cause most disruption in blood sugar and insulin levels including bread, potatoes, rice, pasta and breakfast cereals.

I was reminded about these three patients today on reading a study published yesterday in the journal Gut [1]. In this study, Swedish researchers took a group of adults (average age 26) and put them on a regime which involved limiting their physical activity and getting them to eat two fast food meals each day for four weeks. The participants were monitored in term of, among other things, liver function and weight. Their results were compared with a group of individuals who were not subjected to the regime (these individuals acted as ‘controls’).

Over the course of the 4-week study, those on the fast-food regime put on an average of about 6.5 kg in weight. In particular, waist size increased significantly. The level of the liver enzyme known as ALT (alanine aminotransferase) went up from an average of 22.1 U/L (normal) to 97.0 U/L (abnormally raised). This would be taken, generally speaking, as a sign of liver damage. Not only that, but the fat level in the liver cells of these individuals increased by over 150 per cent. One of the 18 participants developed full blown fatty liver (quite a feat in just four weeks of unhealthy eating).

The findings of this study are reminiscent of Morgan Spurlock antics in the film ‘Supersize Me’. His one-month fast food diet experiment led to significant derangement in his liver enzymes.

So, perhaps not surprisingly, fast food turns out to be bad for our weight and liver. But what was interesting about this study is that the authors looked at the relationship between different elements of the diet and changes in ALT levels. In other words, they wanted to see if they could find out what it was about fast food that seemed to damaged the liver.

Here’s what they found:

Intake of FAT was NOT associated with ALT levels

Intake of PROTEIN was NOT associated with ALT levels

Total CALORIE INTAKE was NOT associated with ALT levels

Intake of CARBOHYDRATE WAS associated with ALT levels

Rather oddly, the authors conclude that this shows that raised liver enzymes can be caused by not just alcohol, but also sedentary behaviour and higher than usual caloric intake. I don’t know why the authors felt the need to draw conclusions that were not supported by their data: remember, it was not an excess of calories that was associated with deranged liver function, but an excess of carbohydrate.

Those of you who watched Supersize Me may remember that the doctor who was keeping a medical eye on Morgan Spurlock at one point told him that his diet was causing his liver to turn into foie gras. The evidence from this study suggests that it was not mere overindulgence nor a high intake of fat that was responsible for the fatty degeneration of Morgan’s liver, but a glut of carbohydrate in this diet.

Any of you wanting to remember that it’s carbs that cause fatty deposition in the liver can do this contemplating the making of foie gras. What is it that geese are force-fed to turn their livers into something that is mainly fat? The answer, of course, is grain.


1. Kechagias S, et al. Fast-food-based hyper-alimentation can induce rapid and profound elevation of serum alanine aminotranferase in healthy subjects. Gut 2008 [epub Feb 14th]

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