Chips and burnt toast 'linked' to low birth weight
There’s food for thought for pregnant women today as the Daily Mail runs two frightening food-based headlines. In its online edition the paper warns that “Pregnant women who eat chips increase their risk of having underweight babies”, and in its print edition it questions, “Could eating burnt toast stunt your unborn baby's growth?”.
The ‘chip chemical’ lurking behind these headlines is acrylamide. It made the news last month after a study found that acrylamide was present in pre-cooked chips (the sort of ‘fries’ served in fast food restaurants).
Acrylamide is produced naturally when foods high in starch, such as potatoes and bread, are fried or baked at high temperatures. The uncertainty about our exposure to acrylamide and its cancer-causing potential has been debated for some time. The current study assessed the potential effects of acrylamide on a developing baby.
Researchers measured acrylamide levels in the umbilical cord blood of babies at birth. They found a general trend that higher acrylamide levels were associated with lower birth weight and head circumference. Babies in the highest quarter of acrylamide levels were, on average, 132 grams lighter than those in the lowest quarter. They also had a comparatively slightly smaller head (3.3mm smaller circumference).
The researchers observed that mothers who reported intake of foods considered higher in acrylamide (such as chips and baked goods) were more likely to have babies with higher acrylamide levels in the cord blood. This suggests that these foods can contribute to higher acrylamide levels in the body, but cannot prove that acrylamide directly causes low birth weight.
Where did the story come from?
The study was carried out by researchers from the Centre for Research in Environmental Epidemiology (CREAL), Barcelona, Spain, and various other institutions in Scandinavia and Europe, and was funded by the European Union, among other local grants. It was published in the peer-reviewed open-access scientific journal Environmental Health Perspectives.
The media headlines suggest that foods containing acrylamides – such as chips and toast – directly affect the growth of a baby. However, this research by itself cannot prove this. Some of the headlines used to report this study also over-simplify a complex situation. For example, The Sun makes the claim: “Junk food as bad for babies as smoking”. The adverse health effects of smoking on pregnancy, such as increased risk of premature birth, low birth weight, cot death (sudden infant death syndrome), stillbirth and childhood asthma, are well known, while the effects of acrylamide in the diet are still being investigated.
What kind of research was this?
Acrylamide is a chemical known to be produced naturally when foods high in starch, such as potatoes, chips, crisps, bread and other cereal and wheat products, are fried or baked at high temperatures.
The uncertainty about the cancer-causing potential of acrylamide has been debated for some time. Acrylamide is currently defined by the World Health Organization as “probably carcinogenic to humans”. This means that while no definitive proof has been found that acrylamide is carcinogenic, as a precaution, exposure to acrylamide should be limited as far as possible.
The UK Food Standards Agency reports that it has funded numerous research projects on acrylamide to understand better how it is formed, and to look at what measures may be taken to reduce levels in food. It says that, “given the uncertainties in exposure and the possible exposure to sources other than food, scientists have concluded that it is not possible to draw any definitive conclusions about the cancer risks of acrylamide in food”.
The current study further investigates acrylamide – this time focusing on how it could affect the developing foetus. Acrylamide is known to cross the placenta and harmful effects have been demonstrated in developing rodents.
This cross-sectional analysis took blood from the umbilical cord at the time of birth and measured levels of acrylamide and its break-down chemical (glycidamide) that were bound to haemoglobin. Heamoglobin is the oxygen-carrying pigment in the blood.
They then looked at whether these levels were associated with the baby’s birth weight and head circumference.
However, this single study cannot prove that acrylamide was directly responsible for any association, as many other biological and environmental factors may be involved.
What did the research involve?
The study involved participants of the NewGeneris research consortium, which is exploring the effect that diet during pregnancy can have on child health. During 2006-2010, the research project enrolled pregnant women from 11 maternity units in cities in Denmark, Greece, Norway, Spain and England.
Mothers completed a food-frequency questionnaire either before, or at the time of, delivery. This included questions about how much they consumed of eight food and drink groups known to contain potentially high levels of acrylamide:
- fried potatoes (chips and crisps)
- breakfast cereals
- crispbread
- coffee
- cookies
- fine bakery products
- bread
- toast
The researchers scored the women on their level of consumption of these items, looking at smokers and non-smokers separately.
Umbilical cord blood was collected immediately after the babies were delivered. The researchers used laboratory methods to measure the amounts of acrylamide and its break-down chemical (glycidamide) that were bound to haemoglobin. They collected information on the baby’s birth weight, head circumference, sex, gestational age (number of weeks of pregnancy at birth) and mode of delivery.
The researchers had questionnaire information, cord blood measurements and baby’s birth measurements available for 1,101 mother and infant pairs.
What were the basic results?
Acrylamide and glycidamide were present in the cord blood from all of the babies. The average acrylamide level was 14.4 pmol/grams of haemoglobin (Hb), and the average glycidamide was 10.8pmol/grams Hb. There was a significant correlation between the two chemicals. This means that as levels of one went up, so did those of the other. Average acrylamide and glycidamide levels were also significantly higher in the cord blood from babies whose mothers smoked compared with babies born to non-smokers.
The researchers found that higher levels of acrylamide and glycidamide in cord blood were associated with a significant decrease in birth weight.
In the whole study group the mean birth weight reduced by 35 grams with each 10pmol/g Hb increase in acrylamide (adjusting for gestational age and country of birth). In the 972 non-smokers only, the mean birth weight reduced by 20 grams with each 10pmol/g Hb increase in acrylamide.
Infants in the highest quartile of acrylamide levels had an average birth weight 132 grams lower than infants in the lowest quartile when the whole population was assessed, and 107 grams lower when non-smokers only were assessed. Reductions in birth weight were similarly seen with each increase in glycidamide level.
Looking at head circumference, each 10pmol/g Hb increase in acrylamide was associated with a 0.6mm reduction in head circumference. The highest versus lowest quartile of acrylamide levels were associated with a 3.3mm reduction in head circumference in the full sample and in non-smokers only. Again, similar associations were observed for glycidamide.
Adjustments for factors such as infant gender and mother’s pre-pregnancy BMI (body mass index), age, previous children, ethnicity, education and dietary pattern (such as intake of vegetables and fruits) did not alter the association between highest acrylamide quartiles and lowest birth weight. Although the adjustments did make the association between acrylamide and head circumference non-significant, which means it could have been the result of chance.
When looking at the acrylamide-rich foods, each one point increase in intake was associated with higher acrylamide (0.68 pmol/grams Hb) and glycidamide (0.39 pmol/grams Hb) levels in cord blood.
How did the researchers interpret the results?
The researchers conclude that dietary exposure to acrylamide during pregnancy was associated with reduced infant birth weight and head circumference. They say that if their findings are confirmed, dietary intake of acrylamide should be reduced among pregnant women.
Conclusion
Acrylamide is a chemical known to be produced naturally when foods high in starch, such as potatoes, chips, crisps, bread and other cereal and wheat products, are fried or baked at high temperatures. Its cancer-causing potential has been debated for some time.
This research aimed to look into potential effects on the developing baby by measuring levels of acrylamide in the cord blood of babies at the time of birth, and associating this with their birth measurements.
All babies were found to have acrylamide in their cord blood (which would suggest that environmental exposure is almost unavoidable), and although an association was observed between higher acrylamide levels and generally lower birth weight and lower head circumference, this cannot definitely prove that acrylamide was responsible.
However, the research did adjust for several potential confounding factors including smoking and some socioeconomic variables. The researchers also observed that mother’s reported intake of acrylamide-rich foods, such as chips and baked goods, was associated with higher acrylamide levels.
This does provide additional evidence suggesting that baked starchy foods contribute to higher acrylamide levels in the body.
The Food Standards Agency does not currently advise people to stop eating foods that could be high in acrylamide, but advises eating a healthy balanced diet, both for pregnant women and the population in general. It also suggests that:
- when making and frying your own chips at home they should be cooked to a light golden colour
- bread should be toasted to the lightest colour acceptable
- when frying or oven-heating pre-prepared foods, such as chips, the manufacturers’ instructions should be followed carefully.
