Eat fruit, but not because of this study

“‘Alzheimer’s cure’ from fruit”, read the headline in The Sun yesterday. “Fruit in the daily diet can stave off Alzheimer’s and Parkinson’s”, the newspaper adds. The Daily Mail said, "extracts from apples, oranges and bananas were found to reduce the damage the illnesses do to neurons – nerve cells in the brain and spine”.

The newspaper story is based on a laboratory study where researchers added extracts from unpeeled apples, oranges and bananas to rat cells, to see if they protected the cells from dying when they were exposed to a toxic chemical. Although the study did find that the extracts protected some of the cells from dying, this doesn’t mean that eating these fruits would have similar effects on human nerve cells in the brain. Furthermore, this study does not look at how eating fruit would stop or slow a complex process such as the development of Alzheimer’s disease.

Although the results of this study cannot make direct links between the benefits of eating fruit and Alzheimer’s disease, there is a large body of evidence showing that a diet rich in fruit and vegetables is beneficial in keeping healthy and avoiding disease.

Where did the story come from?

Professor Chang Yong Lee and colleagues from Cornell University and universities in Korea carried out this research. The study was funded by the Research Promotion Programme at Gyeongsang National University, and the Technology Development Programme for Agriculture and Forestry, Ministry of Agriculture and Forestry, Republic of Korea. It was published in the peer-reviewed scientific journal: Journal of Food Science.

What kind of scientific study was this?

This was an experimental laboratory study looking at the effects of extracts from certain fruits on cells taken from a type of rat tumour. These cells are known to develop into neurons (nerves) when grown in specific conditions in the laboratory.

The researchers grew the rat cells in a dish, then treated them with a toxic chemical – hydrogen peroxide – for two hours. They then looked at how many cells died using a dye that changes colour in the presence of living cells. Exposing the cells to hydrogen peroxide was designed to mimic the process of “oxidative stress”, which is thought to play a role in the development of Alzheimer’s disease.

The researchers then repeated the experiment, but first they treated the cells for 10 minutes with different concentrations of compounds extracted from apples (unpeeled), bananas and oranges. Some cells were left untreated (a negative control) and some cells were treated with quercetin (a positive control), which is a chemical antioxidant found in some fruits and vegetables, including apples. In order to confirm the results, the researchers carried out a similar experiment but used two different ways of checking if the cells had died. These methods looked at whether the membrane surrounding the cell had remained intact or if it had been damaged by the hydrogen peroxide.

What were the results of the study?

The researchers found that treating the cells with fruit extracts before they were exposed to hydrogen peroxide reduced the proportion of cells that died. The higher the concentration of the compound used, the greater the protective effect. The apple extract had the greatest effect, followed by banana and then orange. The results were similar with all three methods that the researchers used.

What interpretations did the researchers draw from these results?

The researchers concluded that eating fresh apples, bananas, oranges and other fruit “may” protect nerves against damage and reduce risk of disorders such as Alzheimer’s disease.

What does the NHS Knowledge Service make of this study?

This study assesses the protective effects of certain extracts from fruits on rat cells in the laboratory, when the cells are treated in a way that might represent the damage they sustain in diseases such as Alzheimer’s. As it’s not yet clear that this method of incubating rat nerve cells with hydrogen peroxide mimics any natural processes in the human brain, it’s not possible to say from this study what effects eating fruit as part of a healthy diet might have on a person’s risk of developing Alzheimer’s. A diet rich in fruit and vegetables is already known to be beneficial in keeping healthy and avoiding disease.

Sir Muir Gray adds...

There is already enough evidence to support the consumption of fruit.