Tuesday August 3 2010
Can chips lead to allergies?
“Children who have junk food diets are at greater risk of allergies as well as obesity,” reported The Daily Telegraph.
This news story is based on research that compared the gut bacteria from children in Italy following a western diet to children from a village in Bukina Faso, Africa, who followed a traditional African farming diet that was richer in fibre. The study found that there was a difference in the bacterial distribution between the children, and that the African children had a higher proportion of bacteria that were able to break down more difficult-to-digest plant sugars and starches. They also found that these children had lower levels of two types of bacteria that can cause diarrhoea.
The researchers said that studying populations with different diets and gut bacteria may help to further our understanding of how a particular diet may contribute to health by promoting the growth of healthy bacteria. However, this study made no link between particular bacteria, diet and illness. Additionally they looked at a Western (Italian) diet in general and did not look specifically at junk food. This study does not provide evidence that eating junk food leads to allergies.
Where did the story come from?
The study was carried out by researchers from the University of Florence in Italy. Funding was provided by the Ministero dell’Istruzione, dell’Universita e della Ricerca and the Meyer Children Hospital. The study was published in the (peer-reviewed) medical journal: Proceedings of the National Academy of Sciences (PNAS).
This study was not covered well by the newspapers, as they overemphasised the potential health consequences of a particular diet. The study did not directly investigate whether there is an association between junk food and allergies or obesity, as the Daily Mail and Daily Telegraph suggest.
What kind of research was this?
This was a cross-sectional study that compared the gut bacteria of children from a village in Africa to that of European children.
The researchers say that as humans have adapted to different environments and diets the diversity of their gut bacteria has changed. They say that in the western world, vaccines, improved sanitation and changes in food production have meant that children have less exposure to bacteria. This may have led to an increase in allergies, autoimmune diseases and inflammatory bowel disease.
The village in Bukina Faso was chosen because the researchers say that the type of subsistence farming that the villagers use resembles the type of farming people used in the Neolithic era 100,000 years ago, to compare a diet that may be similar to our ancestors to a current western diet. They wanted to see whether there was a correlation between diet and the type of bacteria found in the digestive system. They also wanted to investigate whether there was a difference in the distribution of pathogenic bacteria (bacteria that causes illness), given the different hygienic and geographic conditions.
What did the research involve?
The researchers compared the bacteria in the faeces of 14 children from Boulpon in Bukina Faso, and 15 children in an urban area of Florence, Italy. All the children were aged between one and six and had not taken antibiotics or probiotics for the six months before the samples were collected. The children’s mothers were given a questionnaire about their child’s diet.
The children from the Boulpon village were selected as representative consumers of a traditional rural African diet that is low in fat and animal protein and rich in starch, fibre and plant sugars. All of the foods were produced locally. The children from Boulpon typically ate millet grain, black-eyed peas and vegetables with a small amount of chicken and occasionally termites. The children were breastfed up until the age of two. The average amount of fibre in the Bukina Faso diet was 10 grams a day (2.26%) in children aged one to two and 14.2 grams a day (3.19%) in children between the ages of two and six. The diet has a calorie content of 672.2 calories per day for children aged one to two and 996 calories per day for the older children.
To represent a western diet, children were selected who were the same age and size as the children from Bukina Faso. The Italian children were breastfed up to one year and their diet was high in animal protein, sugar, starch and fat and low in fibre. The average fibre content of a European diet is 5.6 grams a day (0.67%) in children aged one to two, and 8.4 grams a day (0.9%) in two-to-six-year-olds. The diet has a calorie content of 1,068.7 calories per day for the younger children and 1,512.7 calories per day for the older ones.
What were the basic results?
The researchers found that more than 94.2% of the bacteria in both groups of children belonged to the Actinobacteria, Bacteroidetes, Firmicutes and Proteobacteria groups.
They found, however, that children from Bukina Faso had a higher proportion of Actinobacteria and Bacteroidetes than the Italian children (10.1% versus 6.7%, and 57.7% versus 22.4%, respectively). Firmicutes and Proteobacteria were more common in the Italian children that the children from Bukina Faso (63.7% versus 27.3%, and 6.7% versus 0.8%, respectively).
They found that three types of bacteria (Prevotella and Xylanibacter, types of Bacteroidetes, and Treponema, a type of Spirochaete) were only found in the children from Bukina Faso. These bacteria (as well as bacterial species that were found in both populations of children) have enzymes needed to break down indigestible plant carbohydrate. This is dietary fibre, starches and sugars that escape digestion in the small intestine but are fermented in the gut to produce short-chain fatty acids (SCFAs). The researchers found higher levels of SCFAs in children from Bukina Faso compared to the Italian children.
The researchers found that two potentially disease-causing intestinal microbes, Shigella and Escherichia, that can cause diarrhoea, were less common in the children from Bukina Faso compared to the Italian children.
How did the researchers interpret the results?
The researchers say that diet has a great effect on determining the gut bacterial content of children. They say that gut bacterial richness could have several health-related effects, including preventing the establishment of disease-causing intestinal microbes. They say that non-infectious intestinal diseases are rarely found in Africans following a traditional diet, and that studying communities such as the villagers in Bukina Faso, who have preserved microbial biodiversity compared to followers of a western diet, may help to determine the role of gut bacteria in health and disease.
This was a small study but it found differences in the gut bacteria between the children who followed a traditional rural African diet and those following a Western diet. This study did not follow up the health consequences of the different types of bacteria found in the children and did not directly assess whether there is a link between a particular type of bacteria and illness, allergies or obesity. The newspapers have linked junk food in particular to allergies and obesity, but this study did not detail the content of the Italian children’s diet.
This study indicates that different diets around the world may have resulted in a different distribution of bacteria found in the gut in different populations. The researchers emphasise that looking further at these distributions may help us to understand which illnesses are diet-related and the role that bacteria play in the promotion and prevention of disease. However, at this point it does not provide evidence linking one type of diet to any illness.