Monday September 24 2007
High GI foods also lead to weight gain
A diet high in white rice, white bread and breakfast cereal could be linked to a potentially fatal liver disease, reported The Daily Telegraph and the Daily Mail. The condition, called fatty liver, “is caused by high consumption of starchy, refined carbohydrates which encourage the body to store energy as fat”, the Telegraph said. Such diets cause "large globules of fat [to] collect in the liver causing it to swell and raising the risk of it failing”, reported the Mail.
The story is based on a study carried out in mice. Researchers found that mice fed a diet of high GI carbohydrates were more likely to have fatty liver disease than those eating a low GI diet. Caution should be taken about extending the findings from this small study in mice to human health. The results do, however, reflect the current understanding of obesity and a diet high in fat (or in foods that are quickly converted into fat storage) as one of the risk factors for fatty liver disease.
Where did the story come from?
Drs Kelly Scribner, Dorota Pawlak and David Ludwig carried out this research at the Department of Medicine at the Children’s Hospital Boston in Massacheusetts, USA. The study was funded by grants from the Charles H. Hood Foundation and the National Institutes of Diabetes and Digestive and Kidney Diseases. It was published in the peer-reviewed medical journal: Obesity.
What kind of scientific study was this?
The research was a small laboratory study conducted in mice. The authors randomised 18 mice to receive either a low GI diet or a high GI diet for 25 weeks. The two diets had exactly the same type and level of fat and protein and only differed in the type of carbohydrate.
The researchers measured food intake and body weight of the mice every day for the duration of the study. They took regular blood samples and used them to assess the concentration of blood glucose and insulin in the mice. The body composition of the mice was also regularly assessed. After 25 weeks the mice were killed and their livers were extracted to determine the presence of liver disease.
What were the results of the study?
The researchers found no difference between the two groups of mice in terms of body weight, blood glucose levels or energy intake. However, the mice fed on the high GI diet had accumulated more body fat than those fed on the low GI diet. They also had higher concentrations of insulin in their blood plasma. There was no difference between the groups in liver weight; however, there was an abnormal accumulation of fat in the liver cells of the mice fed on the high GI diet. This is indicative of fatty liver disease.
What interpretations did the researchers draw from these results?
The researchers conclude that the study has shown that the type of carbohydrate eaten affects the deposition of fat in the liver. The researchers extrapolate these findings to assess the risk of non-alcoholic fatty liver disease (NAFLD) in humans, saying that they “lend support to the possibility that consumption of a high glycaemic index diet increases risk for NAFLD in humans”. Long-term clinical studies (i.e. in humans) are needed.
What does the NHS Knowledge Service make of this study?
This is a study in mice and as such its relevance to human health is limited. It should be considered a preliminary study, for these reasons:
- Though the researchers themselves extrapolate their findings to human health, findings from studies in humans would be more useful. For example, the effects of treating humans suffering from NAFLD with a low GI carbohydrate diet would provide a better understanding of the link between types of carbohydrate in the diet and liver disease.
- This study was small. Only seven mice in the low GI group and eight in the high GI group were available for analysis at the end of the study. Small studies are inherently less reliable than larger ones and the differences seen here may be due to chance. With a larger animal study, more confidence could be placed in the results.
- The study is suggesting a link between high GI carbohydrates and liver disease, not between all starches and liver disease. There are different types of starch and the link between the glycaemic index and “starch” is not simple. The declaration that starch causes liver damage is not accurate.
- Glycaemic index is not the only measure of a food’s nutritional value. Some foods, such as chocolate, are low GI foods but are not particularly healthy because of the high content of saturated fats. The findings from this study should not be interpreted to mean that a low GI diet is the best diet.
It is already understood that both obesity and type 2 diabetes are risk factors for fat deposition in the human liver. Other risks for fatty liver include certain medical conditions, medications and alcohol (leading to alcoholic fatty liver disease). Our understanding of the causes and consequences of NAFLD would be increased by findings from long-term studies investigating the effects of diet and liver function in humans.
Sir Muir Gray adds...
There are already enough reasons to avoid obesity. We know that excess energy intake is associated with changes in the body that can lead to fatty liver, and for some people carbohydrate consumption is one of the causes of their obesity.
In general, all adults need more exercise and most adults need less food and food of different types. Bread, rice and cereals are better than refined carbohydrates, but a carb is a carb is a carb.