Tuesday July 24 2012
Can cheddar cheese really control your blood sugar levels?
Just two slices [of cheese] a day could reduce risk of diabetes, claims the Daily Mail.
The news is based on the results of a Europe-wide study that aimed to determine whether eating a diet high in dairy products is associated with a change in your risk of developing type 2 diabetes.
Overall, there was no association between total dairy product intake and diabetes risk. However, the results suggested that people who did eat a lot of cheese and other fermented dairy products (such as yoghurt and buttermilk) may have a lower risk of developing diabetes. This is despite no significant connection between eating more of one particular dairy product and reduced risk of diabetes.
However, the difference in risk varied widely from country to country – people in France who ate more cheese had a reduced risk, while those in the UK who ate more cheese were at increased risk. While the researchers did not examine the types of cheese eaten, it would be interesting and delicious to examine whether this could play a role. When the results were pooled, the possible preventative effects could well be due to chance, not cheese.
So the Mail’s claims that ‘eating lots of cheese’ can ‘beat diabetes’ is full of holes. There are currently far more established methods of reducing your risk of diabetes, such as:
- losing weight if you are overweight
- taking regular exercise
- eating a healthy balanced diet
Where did the story come from?
The study was carried out by researchers from European research centres and universities, including the MRC Epidemiology Unit in Cambridge, Oxford University and Imperial College London. The EPIC-InterAct study was funded by the European Union, although the individual researchers were also supported by other organisations. The study was published in the peer-reviewed The American Journal of Clinical Nutrition.
This story was covered in the Daily Mail, Daily Express and The Daily Telegraph. The Mail’s headline focused on the ‘two slices’ of cheese without giving useful information such as weight or cheese type. The Express states that “research shows that regularly snacking on cheese can slash the chances of getting type 2 diabetes by 12 per cent”, while the Telegraph also runs with this figure. This result of the study is based on a comparison of people who ate the most (more than 56g per day) versus the least (less than 11g per day) cheese. So, the idea of ‘snacking’ on cheese or just ‘two extra slices’ may give a misleading impression of the extremely large amounts of cheese that would need to be eaten every day. As the study’s results for cheese were not significant, it renders this advice redundant.
What kind of research was this?
This was a nested case-cohort study. Participants were selected from the European Prospective Investigation into Cancer and Nutrition study, a large prospective cohort study that followed up 340,234 people for 3.99 million person-years, during which time 12,403 people developed type 2 diabetes. They compared the dairy intake of these people (cases) with a random selection of people in the study (16,835 people) to see whether dairy product intake was associated with risk of developing diabetes. This is an appropriate study design to address this question, although this study type cannot show causation, only association.
What did the research involve?
The researchers collected dietary information at the start of the study using a quantitative dietary questionnaire, with individual portion sizes or validated semi-quantitative food-frequency questionnaires. A random sample of people were also asked to recall what they had eaten and drunk in the previous 24 hours. The researchers collected data on the intake of milk, yoghurt and thick fermented milk (products such as soured cream and crème fraîche), and cheese. The researchers also collected data on the participants’ lifestyle and medical history.
The researchers then divided intake of total dairy products (defined in this study as the total intake of milk, yoghurt and thick fermented milk, and cheese) and the individual subtypes of dairy into fifths, and compared the risk of developing type 2 diabetes in each fifth. The researchers adjusted dairy product intake for total calorie intake. The researchers also looked to see if there was a trend, for example if risk decreased with increasing intake. The researchers also adjusted for potential factors that could be responsible for any association seen (confounder) including:
- body mass index (BMI)
- physical activity index
- smoking status
- alcohol consumption
- other dietary factors
The researchers also looked to see whether any observed association was due to the fact that dairy products are good sources of calcium, magnesium and vitamin D.
What were the basic results?
Total dairy product intake was not associated with the risk of type 2 diabetes (hazard ratio for the comparison of highest intake compared to lowest intake 1.01, 95% confidence interval 0.89 to 1.23 in the fully adjusted model).
Yoghurt and thick fermented milk intake, and cheese intake, were associated with a reduced risk of type 2 diabetes, but this was not significant. The hazard ratio for the comparison of highest intake of yoghurt and thick fermented milk compared to lowest intake was 0.91 (95% confidence interval 0.81 to 1.02 in the fully adjusted model). The hazard ratio for the comparison of highest intake of cheese compared to lowest intake 0.88 (95% confidence interval 0.76 to 1.02).
Cheese did have an inverse association with diabetes (ie eating more cheese appeared to lower the risk of diabetes), but this was not significant when all confounding factors were adjusted for. When fermented dairy products were combined (yoghurt, thick fermented milk and cheese) higher intake was associated with significantly reduced risk of diabetes. The hazard ratio for the comparison of highest intake compared to lowest intake 0.88, 95% confidence interval 0.78 to 0.99.
How did the researchers interpret the results?
The researchers conclude that “this large prospective study found no association between total dairy product intake and diabetes risk. An inverse association of cheese intake and combined fermented dairy product intake with diabetes is suggested, which merits further study”.
This well-designed study found that overall, total dairy product intake was not associated with either increased or reduced risk of developing type 2 diabetes. Sub-analyses according to type of dairy product did find that people with the highest intake of fermented dairy products (total of yoghurt, thick fermented milk and cheese) were at reduced risk of developing diabetes. However, analyses according to the individual products did not find significant associations, so any advice based on particular foods is likely to be misleading.
There was a trend for increasing cheese intake to be associated with reduced risk of diabetes, although the difference in risk in people eating the most and the least cheese was not statistically significant. Similarly, though there was a trend for intake of yoghurt and thick fermented milk to be associated with reduced risk of diabetes, this trend was not statistically significant.
These findings merit further study. This study had many strengths (including its design, the number of participants, the length of follow-up, range in dairy intake and adjustment for confounders), but it did have some limitations. Limitations of this research included the facts that dairy intake was self-reported and that data on low- and high-fat dairy product intake wasn’t collected. It would also be interesting to determine how these products might influence this reduction in risk. The authors suggest that it could be due to the types of fats contained in these products, or due to the presence of probiotic bacteria. However, these things have not been further examined by this study.
While it is not known for definite whether or how intake of dairy products may affect your risk of diabetes, the best ways to reduce risk are to aim to lose weight if you are overweight or obese, take regular exercise, and eat a healthy, balanced diet.
Read more about preventing type 2 diabetes.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on twitter.