Wednesday August 6 2014
Not all saturated fat is bad, suggests the report
Saturated fat in cheese, yoghurt and other dairy products may protect against diabetes, report the Mail Online, The Daily Telegraph and The Independent.
A study has found that people with higher levels of the types of saturated fatty acid found in dairy products were less likely to develop type 2 diabetes.
Saturated fat – found in butter, cheese and red meat – is generally considered unhealthy and linked to high levels of cholesterol and heart disease, as well as type 2 diabetes.
Researchers looked at blood samples that had been taken from 12,132 people before they developed type 2 diabetes, and compared them with samples obtained from 15,164 healthy people who did not go on to develop diabetes. All participants were from across Europe.
Different types of saturated fat can be identified by looking for chain-like saturated fatty acid molecules, which contain either an odd or even number of carbon atoms.
Analysis of the samples revealed that people with higher levels of “even-chain” fatty acids were more likely to develop diabetes.
Even-chain saturated fatty acids were more likely with diets high in alcohol, soft drinks, margarine and potatoes, although the body can also produce this type of fatty acid.
People with higher levels of “odd-chain” fatty acids in their blood samples were less likely to develop the condition.
Odd-chain saturated fatty acids were more likely through diets high in dairy products, cakes and cookies, nuts and seeds, and fruit and vegetables.
Overall, this study can only tell us that there is an association between the levels of these fatty acids and the risk of developing diabetes – it cannot prove they had a role in causing the condition.
This study furthers understanding of the biological processes that may be associated with type 2 diabetes, but it cannot say that eating dairy is going to cut your risk of getting this chronic disease.
Despite this, the increased risk from a larger waist circumference, being overweight or obese mean that the amount you eat still needs to be balanced to avoid excess weight gain.
Where did the story come from?
The study was carried out by researchers from the University of Cambridge, MRC Human Nutrition Research in Cambridge, the University of Oxford and other universities across Europe. It was funded by the European Commission, the Medical Research Council and the Cambridge Lipidomics Biomarker Research Initiative.
The study was published in the peer-reviewed medical journal The Lancet Diabetes and Endocrinology.
This study was not accurately reported by most media outlets. Contrary to several reports, the study did not prove that saturated fat from dairy products are not bad for health or that they “beat” diabetes. It only showed that people with a one-off reading of a higher proportion of these types of fats compared to other saturated fats had a reduced risk of developing diabetes. It did not look at any other health outcomes related to dietary intake of dairy products.
The study was also not able to say that people with higher levels of the even-chain saturated fatty acids will develop diabetes, it is only able to show an increased risk.
What kind of report was this?
This was a prospective case-cohort study, which looked at the blood levels of different types of saturated fat in people who developed diabetes, compared to a control group who did not develop diabetes over the next 16 years.
They aimed to see if there was a link between any of the nine different types of saturated fatty acids that they measured and type 2 diabetes. As this was a cohort study, it can only show an association between with the levels and the risk of developing diabetes during the study's timeframe. It cannot prove causation.
What did the research involve?
The researchers used data from a large study called the EPIC cohort, which followed 340,234 people from eight European countries from 1991 to 2007. From this study, they identified all 12,132 people who did not have a diagnosis of diabetes at the beginning of the study, but who developed diabetes at some point during the 16-year follow-up.
They also randomly selected 15,919 people who did not develop type 2 diabetes. All participants had provided a blood sample at the beginning of the study. They worked out which of these people developed diabetes during the study period from at least two of the following sources: self-report, primary care and secondary care registers, drug registers, hospital admissions and mortality data. This gave them a subgroup of 15,164 people who did not develop type 2 diabetes.
The average age of the participants was 52.
From the blood sample, they measured the levels of nine different types of saturated fatty acids and HbA1C, which is an indicator of type 2 diabetes.
Participants’ weight and height were measured by trained professionals to calculate BMI, and most participants also had their waist size measured. The participants filled in questionnaires on medical history, smoking status, educational level, physical activity level and usual diet over the previous 12 months.
They compared the levels of the different types of saturated fatty acids in the group of people who developed diabetes, compared to those who did not.
What were the basic results?
Higher proportions of even-chain saturated fatty acids were associated with a 43% increased risk of type 2 diabetes, hazard ratio (HR) 1.43 (95% confidence interval (CI) 1.29 to 1.58). There was also a higher proportion in older adults, people with higher BMI and men. Higher even-chain saturated fatty acids were more likely with diets higher in alcohol, soft drinks, margarine and potatoes, and less likely with fruit, vegetables, olive oil and vegetable oil.
Higher proportions of odd-chain saturated fatty acids (mainly from dietary dairy fat intake) were associated with a 30% reduced risk of developing type 2 diabetes, HR 0.70 (95% CI 0.66 to 0.74). The proportion was also higher in people with a lower BMI and women. Higher odd-chain saturated fatty acids were more likely with diets higher in dairy products, cakes and cookies, nuts and seeds, and fruit and vegetables.
Higher proportions of longer-chain saturated fatty acids were associated with a 30% reduced risk of type 2 diabetes, HR 0.70 (95% CI 0.59 to 0.85). Little is known about these fatty acids, but they were associated with a lower alcohol intake.
The results remained significant after taking into account multiple potential confounding factors, such as age, BMI and waist size.
How did the researchers interpret the results?
The researchers concluded that odd-chain fatty acids, which mainly come from dairy fat in the diet, are associated with a decreased risk of developing type 2 diabetes. However, they point out that they were not able to rule out the possibility that this association was due to other nutrients present in dairy products, such as vitamin D, calcium or the fermentation process of dairy products.
They also found that even-chain fatty acids are associated with an increased risk of developing type 2 diabetes, but this relationship is more complex and not just related to diet. Even-chain fatty acids can come from a variety of places and not just dietary fat, such as carbohydrates and alcohol, and they can also be produced by the body.
Researchers say further research is required to gain a better understanding of the role of diet in this process before they can confidently advise on dietary intake of saturated fats.
Finally, they report that little is known about the origin or production of longer-chain fatty acids, and they suggest that this should be another area for future research.
This study has found an association between higher levels of odd-chain and long chain fatty acids, and a reduced risk of developing diabetes. Higher levels of even-chain fatty acids were associated with an increased risk of developing diabetes.
Strengths of the study include:
- the large number of participants and diversity, coming from eight European countries
- a wide range of diets
- prospective nature of the study, capturing blood levels before diabetes onset
- diabetes status was not determined by self-report only
However, limitations of the study include:
- The blood measurement of the saturated fatty acids did not measure the overall amount of saturated fatty acids in the blood, it just looked at the proportion of the different types of saturated fatty acids in each individual. This means that some people may have had high overall levels of saturated fatty acids and some could have had low levels.
- The blood sample was only taken once at the beginning of the study, and this may not have been representative of normal levels, which fluctuate through diet and activity levels.
- Reliance on dietary questionnaires being completed accurately.
This study suggests that not all saturated fat may be bad and that the type of dietary saturated fats influence the risk of diabetes, but it does not conclusively show that dairy products are protective. Whatever the case, the increased risk from a larger waist circumference, as well as being overweight or obese, mean that the amount you eat still needs to be balanced to avoid excess weight gain.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.