Monday January 17 2011
The study does not show which type of milk is healthier
“Organic milk is better for you,” reports The Independent today, adding that an analysis of milk sold in UK supermarkets has found that organic milk has lower levels of harmful saturated fats than conventional milk. The newspaper says organic milk also contains higher levels of beneficial fatty acids.
The study behind this coverage has analysed the fat content in 22 brands of milk available in UK supermarkets, including 10 organic brands. It found that, overall, organic milk contained significantly higher levels of polyunsaturated fats, which are thought to be beneficial for health. However, there was no difference in overall levels of saturated fat, so suggestions that the study found organic milk to be “less fatty” were inaccurate. There were also seasonal variations in the differences, which were more pronounced in the summer, and other differences likely to be linked to the quality of the cows' food.
This well-conducted research may guide people to the organic section of the supermarket, but as a laboratory-based analysis it has not directly linked these differences to actual differences in health outcomes and therefore does not prove that organic milk is better for you than conventionally produced milk.
Where did the story come from?
This study was carried out by researchers from Newcastle University and funded by the European Community and Yorkshire Agricultural Society. The study was published in the peer-reviewed Journal of Dairy Science.
The newspapers have reported the methods and intentions of the research accurately, although some headlines have oversimplified or misinterpreted the findings of the study. The study does not conclude that organic milk is less fatty or better for you than conventionally produced milk. Instead, it has given a detailed profile of the various polyunsaturated and saturated fats found in the two types of processed milk.
What kind of research was this?
Organic produce is popular in the UK, and in this study researchers wanted to explore the nutritional content of organic milk. They explored the issue based on three objectives:
- to compare the fat content of organic and conventionally produced milk in bottles that ordinary consumers would buy in supermarkets
- to determine whether there were particular differences between different brands of milk
- to rule out any effects produced by processing the milk, i.e. how pasteurisation might affect the fat content.
Other research has not provided consistent results on the fat profile of organic milk, so the researchers hoped to add to this body of evidence.
What did the research involve?
This was observational research in which researchers sampled 22 brands of milk sold in UK supermarkets, sampling each on four occasions over a period of two years. They were careful to sample milk from both the summer and winter seasons, because milk produced in the summer generally contains a different mixture of fatty acids, and they therefore needed to ensure that these seasonal fluctuations did not cloud their results.
The researchers included the 22 brands for which they had collected a sample at each of the four time points. There were ten organic milks in their overall set for analysis. They did not include UHT milk, milk fortified with additional vitamins or minerals, or those that were labelled as coming from a minority breed of cow.
Standard analyses for fat, protein and lactose content were carried out on all the milk samples. Researchers were particularly interested in comparing the constituents of organic versus conventionally produced milk, and specifically the levels of certain polyunsaturated fats, including linoleic acid and alpha-linoleic acid.
Some polyunsaturated fatty acids are considered better for health than others, although all are important. Among these most important fatty acids are two groups called the n3-PUFA and n6-PUFA fatty acids. The researchers also measured the ratios of these substances, known as the n3:n6 ratio, found in organic and conventionally produced milk.
The researchers compared the profiles of organic against conventionally produced milk, the milk produced in summer against winter milk, and also the year in which it was sampled (first year versus second year of the study).
What were the basic results?
Overall, organic milk had higher concentrations of beneficial polyunsaturated fats than conventional milk, although there was no significant difference in the total fat or protein content. Organic milk had 24% higher total polyunsaturated fatty acids.
Of the two types of milk, organic milk had significantly higher levels of several PUFAs that have been associated with health benefits in other research. These included vaccenic acid, conjugated linoleic acid, alpha-linoleic acid and eicosapentaenoic acid. Organic milk also had a more desirable n-3:n-6 ratio. The differences between the compositions of the two milks was smaller in winter than in summer, although they remained statistically significant for both seasons.
Between organic and conventional milk, there was no difference in the total amount of saturated fatty acids, but there were differences in the mixture of individual saturated fatty acids that made up this total. This included significantly more myristic acid in organic milk, which is thought to carry a high risk of coronary heart disease, although this was only significant in the summer of the second year of sampling.
They also note that the year of the sampling had an effect on the milk composition, suggesting that different climatic conditions and food availability for cows may affect milk quality.
How did the researchers interpret the results?
The researchers say that their study confirms that organic milk has higher concentrations of beneficial unsaturated fatty acids, and that this difference is greater in summer. They acknowledge that there are seasonal differences and differences that may be due to the quantity and quality of food available for the cows.
This was a well-conducted observational study comparing samples of milk from UK supermarkets and assessing whether there are differences in the fatty acid profiles of organic and conventionally produced milk. The study found that, overall, organic milk had higher levels of certain beneficial polyunsaturated fats than conventional milk, although there was no overall difference in their total saturated fat content. Organic milk did, however, contain more myristic acid – a saturated fat that is thought to increase the risk of coronary heart disease.
Newspapers have taken different slants on the reporting of these results, particularly in their headlines. However, it is an oversimplification to state that organic milk is less fatty than ordinary milk, or that it has less “harmful fats”, as The Daily Telegraph and the Daily Mail have done. However, the study itself found that the two milk types contained in the same levels of saturated fat.
Although the press did not report this clearly, the research actually found that organic milk contains higher levels of of certain beneficial polyunsaturated fats. These fats showed a seasonal variation and other differences that were probably linked to the diet of the dairy cows.
While these are interesting results that warrant further investigation, it is not possible to conclude from this laboratory-based study that organic milk is “better for you”, only that it contains a different mixture of fats from milk produced conventionally. Despite these variations, milk is rich in a number of important nutrients, particularly calcium, so it is sensible to include it as part of a balanced diet, choosing lower-fat varieties such as skimmed and semi-skimmed when trying to keep fat intake down.
The decision to consume organic milk is a personal one, and other factors such as cost and animal welfare can play an important role in helping an individual to decide. However, based on this study alone, it is not yet possible to tell whether it delivers any additional health benefits.