Low-fat dairy foods & diabetes risk

I woke up on the morning of Thursday 6th February 2014 to a number of tweets informing me that headlines were claiming “yoghurt is key to beating diabetes.” The on-line version of the Express moderated the headline to “How low-fat dairy food can help to cut your diabetes risk” but the story was all over the news from Australia to India.

This study in the journal Diabetologia was the source article. It is available for free download (as of the time of writing), which is helpful.

The study

There is a study going on across Europe called the European Investigation into Cancer Study (EPIC). It started in 1991 and I just happen to be one of the UK members. I get questionnaires every few years asking me to share health details and asking me what I ate over the previous year. This blog post has a link to the questionnaire.

The Norfolk part of the EPIC study (this is called a cohort) has 25,639 men and women. They were aged 40-79, when they were recruited into the study between the years 1993-1997. The numbers in the Diabetologia paper are confusing at times. It appears that this diabetes/dairy study has randomly selected 4,127 participants – 753 with known cases of type 2 diabetes from the full cohort and 3,502 as a subcohort. This 3,502 group also contains cases of type 2  diabetes (as a valid random selection will reflect the original group). There are 128 cases of type 2 diabetes in the subcohort of 3,502. (Incidents of type 2 diabetes were recorded up to 31 July 2006. There were 892 in the whole study – 25,639 people – giving an incident rate of 3.5%.)

Don’t worry about any of this. It will soon become irrelevant.

I then tried to work out when the dietary questionnaire was undertaken. Is this diabetes/dairy study relying upon the initial food diary questionnaire completed on entry? Or one undertaken during the study? The paper says “Baseline dietary intake data were collected using a 7 day food diary [Reference 15].” Reference 15 is dated 2001 and describes the general method for the Norfolk EPIC study. Does this mean the study is relying upon a food diary from between 1993 and 1997 – baseline entry to the study?

I read on a bit and realised that this too is irrelevant. And this is why…

The characteristics of the subjects

Table 2 is the important one on the study. It puts the 3,502 subcohort people into three groups – those with total dairy intake under 183 grams per day; those with total dairy intake between 184-312 grams per day and those with total dairy intake over 313 grams per day. These may seem strange groups – but they’ve just split the 3,502 into equal numbers of people and seen where the lowest, middle and highest thirds of dairy intake fall.

Table 2 tells us that we ended up with no age differences between the three groups (all had an average age of 59). However that’s where the similarities ended.

 

TABLE 2 in the paper Tertile 1 Tertile 2 Tertile 3
g/day ≦ 183 184-312 ≧ 313
People in group 1,168 1,167 1,167
Mean (average) age 59 59 59
Total dairy intake – mean g/day 116 245 447
Men (% of group) 40.5% 41.1% 48.5%
Related factors lifestyle:
Alcohol (units/week) 8.5 6.6 5.4
Smoking (% current smokers) 14.1% 10.7% 9.6%
Physical activity (% active) 15.6% 19.9% 21.8%
BMI (mean) 26.8 26.2 25.8
Waist circumference (men) – mean in cm 97.5 95.7 93.9
Waist circumference (women) – mean in cm 82.4 81.4 81.3
Dietary factors:
Saturated fat (% total energy) 12.9% 12.9% 13.1%
Mononunsaturated fat (% total energy) 12.3% 11.9% 11.6%
Polyunsaturated fat (% total energy) 6.7% 6.6% 6.2%
Calcium intake (mg/day) 624 807 1,077
Magnesium intake (mg/day) 256 289 330
Vitamin D intake (mcg/day) 2.38 2.85 2.98

 

The claim

The Abstract of the paper (the summary) states:

“Results: Total dairy, high-fat dairy, milk, cheese and high-fat fermented dairy product intakes were not associated with the development of incident diabetes. Low-fat dairy intake was inversely associated with diabetes in age- and sex-adjusted analyses (tertile [T] 3 vs T1, HR 0.81 [95% CI 0.66, 0.98]), but further adjustment for anthropometric, dietary and diabetes risk factors attenuated this association.”

In simple terms this is saying:

– We found NO association (positive or negative – no association at all) between the incidence of type 2 diabetes and total dairy OR high-fat dairy OR milk OR cheese OR high-fat fermented dairy products. NO ASSOCIATION AT ALL.

– The claim is then that low-fat dairy intake was inversely associated with diabetes when we only adjusted for age and men/women i.e. a higher intake of low-fat dairy was associated with a lower incidence of diabetes with virtually no data adjustment. This still says nothing about causation. It merely says we observed two things together when we didn’t adjust for things that we need to adjust for.

– The final part says that – when we did properly adjust for all the things that were different, the observation was “attenuated”. This is so disingenuous it’s scandalous. It should have said from the outset, when we adjust for all the differences between the groups there is no association whatsoever between low-fat dairy and diabetes. There is nothing to observe. We have found nothing and there need be no newspaper headlines.

There are 3 models in the paper:

Model 1 adjusts for age and sex and nothing else – that’s the one they use to claim an inverse association between low-fat dairy and incidence of diabetes. Table 2 tells us that there is no difference in age – all groups have an average age of 59. There are more men in the higher dairy group, but so what?

Model 2 adjusts for BMI, family history of diabetes (which is not in table 2 for some unknown reason), smoking, alcohol, physical activity and other lifestyle attributes. We can see from Table 2 that the lower dairy group have 1.6 times the alcohol unit intake of the higher dairy group. The lower dairy group has one and a half times the percentage of current smokers. The lower dairy group has 70% of the physically active people in the higher dairy group. The lower dairy group have higher BMIs and larger waistlines. All of these favour the higher dairy intake having less incidence of diabetes and this having nothing to do with dairy, but lots to do with alcohol, smoking, activity, weight and waist size. And sure enough – when the data is adjusted to compensate for these stark differences, the association disappears.

Model 3 then further adjusts for dietary differences – energy intake, vegetables (higher in the higher dairy/lower diabetes group), processed meat (lower in the higher dairy/lower diabetes group)etc and this also eliminates, sorry, attenuates, any associations.

I was amused by the fact that group 3 – with the higher dairy intake and lower incidence of diabetes also had the highest saturated fat intake, lowest monounsaturated fat and lowest polyunsaturated fat intake, but that didn’t make the headlines. Less amusing is the difference in calcium, magnesium and vitamin D intake between the three groups. What impact did that have on health?

If you like stats, table 3 in the paper shows you all of this. This table takes the lower dairy tertile as being the baseline of 1 and then looks at the middle intake of dairy and the higher intake of dairy relative to this – for models 1, 2 and 3.

Each row gives a mean (average) and then the 95% confidence interval in this kind of format: 0.93 (0.74-1.18). This means that the average was 0.93 but that the confidence ‘range’ around this average lies between 0.74 and 1.18. a) That’s quite wide and b) the number 1 falls within this range so this is not seen as significant – because the comparator of 1 falls within both groups.

You can use this principle to see at a glance – as the paper reported – that nothing is significant for total dairy, high-fat dairy, milk, cheese or high-fat fermented dairy. Low fat dairy is only significant for model 1 – with none of the adjustments that need to be made. There is no association when the lifestyle factors are properly taken into account. Ditto – the association with fermented dairy disappears as soon as lifestyle factors are properly taken into account.

Only one factor nudges out of the significant range. Look at the last line in table 3. The upper limit of the standard deviation is 0.99 – just a notch away from touching the line of no significance and this is for low-fat fermented dairy. And it’s association, not causation. And it’s about relative, not absolute risk. Do you think that was worth today’s headlines?!

 

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17 comments on “Low-fat dairy foods & diabetes risk
  1. avatar Carlo says:

    Zoe,
    More weird statistics on “meat and diary” consumption on todays daily mail online…the article seems to state that meat and diary are as bad as smoking in your 50s but good in your 60s…doesn’t seem right, does it?
    Thanks
    Carlo

    • avatar Zoë says:

      Hi Carlo – I’m just looking at it now – full article here. It’s about protein – not fat for once!

      The article says that there was no association when they looked at all the subjects (6,381 people aged 50 and over) between protein intake and all cause mortality, cancer mortality and CVD mortality. However, when they split the subjects into 50-65 and over 65 they found an association between high protein intake and high cancer mortality (and through this all mortality) and conversely an association between high protein intake and low cancer mortality (and low all cause mortality) in the higher group. Which has to happen. If all people together show no association then – if split into two groups – if one shows a positive association, the other must show a negative association.

      You’re right to say – why? It doesn’t make sense at face value. The paper tries to leap from ‘men’ to mice to say what they’ve observed in mice to try to find an explanation. I lost the will at that point. I’m pondering a theory and will blog if it gets anywhere!

      Best wishes – Zoe

  2. avatar Mie says:

    And once again, the crank responds with a temper tantrum rather than addressing the facts.

    FYI, I’m polite to those who deserve it, regardless of whether I agree with them on a particular matter or not. Trolls, denialists and conspiracy nuts get what they deserve from me. No more, no less. So I suggest you take a good, long look in the mirror.

  3. avatar Robin Willcourt says:

    Your response is so “Mie” Spot on! Lots of arm waving and mandibular ejaculations!
    Clearly not possible to have a discussion about important points.

    Your use of childish adjectives would be better in a comic strip than on a board where people who are genuinely concerned about the subversion of their rightsand their health by industries that are making us sick and sicker.

    Your consistent use of disparaging adjectives to any who oppose your views serves only to tell us what we all know about people who have nothing to contribute when faced with facts that challenge their own beliefs. and that is to resort to name calling. I am not going to discuss this further with you as there is no point arguing with an ignorant bully.

  4. avatar Mie says:

    Robin

    “Epidemiological studies do not give you mechanisms, they point to correlations after which properly conducted science (seriously lacking in this particular domain) might give answers to mechanisms of action.”

    And I didn’t claim otherwise. The conjunction “and” in my sentence seems to have confused you.

    “The probability that a recent foodstuff in our evolutionary life is likely to lower the risk of diabetes but an as yet unspecified action via an observational study conducted in a sloppy manner is, well, unlikely.”

    Dairy products aren’t that “recent” and the evolutionary aspect is (in this sense and many other – e.g. paleo nonsense) misguided as it can be used to argue anything/everything under the Sun, thus ignoring the fact that in science evidence matters – not extrapolation based on shaky grounds. There’s convincing evidence of the health effects of dairy products, especially fermented dairy products, which cannot be dismissed without actually taking a closer look at such studies where it has been observed and/or studies that have tested possible mechanisms behind these benefits.

    “This is the pseudoscience that says statins lower death rates. It’s right up there with global warming, er, climate change.”

    Yep, Internet crankism indeed: denying observed facts. You don’t have to keep it up, I already believe you’re a “man of faith”.

    “FYI, the funding of any given study is RIGHT at the heart of whether it is biased or not.”

    Err, if the study is biased up to the point of being invalid then this can & will be observed from the study itself, how it relates to other studies in the same field, whether it has been/can be replicated etc. etc. The VERY basis of scientific inspection is that funding is at best secondary point of interest and a study isn’t rendered invalid/unscientific on these grounds alone. Saying “Nissen” or “Poldermans” won’t change anything more than shouting “Hume” or “Popper”.

    “True but not likely to ever happen… ”

    Of course not. Cranks who don’t have the knowhow will always continue to dismiss studies because they’ve been funded by Big Pharma/grain producers/etc. instead of offering actual criticism of such studies. That’s how you operate because you’re not capable of anything better. Never you mind the fact that since this leads to EVERY study being “biased” in one way or another, the whole concept of scientific inspection would lose its purpose.

    In the end, that’s what you’re after, right?

  5. avatar Robin Willcourt says:

    Mie, I have read so many of your comments on other sites. You’re good at your sarcasm, so I could’t help but respond somewhat in kind. Epidemiological studies do not give you mechanisms, they point to correlations after which properly conducted science (seriously lacking in this particular domain) might give answers to mechanisms of action.

    The probability that a recent foodstuff in our evolutionary life is likely to lower the risk of diabetes but an as yet unspecified action via an observational study conducted in a sloppy manner is, well, unlikely. This is the pseudoscience that says statins lower death rates. It’s right up there with global warming, er, climate change.

    FYI, the funding of any given study is RIGHT at the heart of whether it is biased or not. Can you say Steven Nissen?
    Don Poldermans?

    “The primary focus is/should always be on the study itself.” True but not likely to ever happen… read Peter Gotzsche and think again.

  6. avatar Mie says:

    Robin gets emotional:

    “Mie has never met a drug company sponsored “result” that he has not agreed with.”

    Is that so? I strongly doubt that you’ve read all my comments on these matters, so I’ll put this down as a childlike burst of emotions.

    “The idea that a dairy product might lower the risk for anything, is, well, funny.”

    Care to explain why? We have knowledge of potential mechanism and evidence from epidemiological studies, so why is that funny?

    “I’d say to Mie …”

    … and I’d reply that you just succeeded in sounding like a classic Internet crank. FYI, the funding of any given study is at best a secondary point of interest. The primary focus is/should always be on the study itself.

  7. avatar Robin Willcourt says:

    Zoe…. Mie has never met a drug company sponsored “result” that he has not agreed with. A shill is, well, a shill. The idea that a dairy product might lower the risk for anything, is, well, funny.
    I’d say to Mie, “Get serious!” You have not a single thread of CREDIBLE evidence that your stance on the causes of CVD is based in fact. DO NOT bother to quote food or drug industry funded studies to bolster your position.

  8. avatar Mie says:

    Dana wrote:

    “Good luck absorbing the calcium in dairy without enough fat to go along with it. We get too much calcium in the modern Western diet relative to other minerals anyway, but if you think we need more calcium, low-fat or skim is a ridiculous way to try to get it.”

    Just because you consume low-fat dairy products during a meal doesn’t mean you won’t get any fat during the meal. Kinda obvious, isn’t it?

  9. avatar Dana says:

    It gets even more fun. I was looking up info about a certain analogue of vitamin K. It’s vitamin K2, analogue mk-4, also known as menaquinone-4 or menatetrenone. I’d been hearing all sorts of crazy stuff about it and wanted to verify.

    Just by hitting Wikipedia I learned this:

    Menatetrenone encourages the production of osteocalcin, a mineralized protein found in bones and in tooth dentin.

    Osteocalcin encourages the production of a chemical called adiponectin by the fat tissue.

    Adiponectin in turn increases insulin sensitivity all over the body.

    Guess where you find menatetrenone? Animal fat.

    Guess what they’re telling us not to eat anymore? Three guesses and the first two don’t count.

    P.S. Good luck absorbing the calcium in dairy without enough fat to go along with it. We get too much calcium in the modern Western diet relative to other minerals anyway, but if you think we need more calcium, low-fat or skim is a ridiculous way to try to get it.

    • avatar Zoë says:

      Hi Dana – why are we having to discover this for ourselves?! Below is an extract from my obesity book with another interesting on vitamin K:

      “Vitamin K comes in two forms: K1 and K2. K1 is found in plants, green leafy vegetables particularly, and is also called phylloquinone. Vitamin K2 is found in animal foods. K2 is also known as menaquinone and comes in different forms – MK-4 through to MK-10 (the ‘MK’ comes from a phonetic abbreviation of MenaKwinone). Meat is a primary source of MK-4. Eggs and calcium rich hard cheese are particularly good sources of MK-7, 8 and 9. The Rotterdam Study concluded: “Intake of menaquinone was inversely related to all-cause mortality and severe aortic calcification. Phylloquinone intake was not related to any of the outcomes. These findings suggest that an adequate intake of menaquinone could be important for CHD prevention.” I share this as another example of the animal form of fat soluble vitamins being the most useful – in the context of current public health advice steering us away from these nutritious foods.”

      (Ref Geleijnse JM, Vermeer C, Grobbee DE, Schurgers LJ, Knapen MH, van der Meer IM, Hofman A, Witteman JC, “Dietary intake of menaquinone is associated with a reduced risk of coronary heart disease: the Rotterdam Study”, The Journal of Nutrition, (November 2004). )

      Keep doubting and discovering!
      Very best wishes – Zoe

  10. avatar Mie says:

    Your attempt for criticism has several problems.

    1) You stated:

    “I was amused by the fact that group 3 – with the higher dairy intake and lower incidence of diabetes also had the highest saturated fat intake, lowest monounsaturated fat and lowest polyunsaturated fat intake, but that didn’t make the headlines.”

    Maybe because the differences were minuscule? E.g. safa: 12,9% vs 13,1%. Trivial.

    2) And continued: “Less amusing is the difference in calcium, magnesium and vitamin D intake between the three groups. What impact did that have on health?”

    Perhaps you ought to try to answer that question yourself? The only difference in terms of diabetes – in my opinion – might have come from the difference in vitamin D, but that was insignificant.

    3) “This is so disingenuous it’s scandalous. It should have said from the outset, when we adjust for all the differences between the groups there is no association whatsoever between low-fat dairy and diabetes. There is nothing to observe. We have found nothing and there need be no newspaper headlines.”

    Have you ever read a research article? It’s common practice to report attenuated findings later. Anyways, the idea is to read the ENTIRE article – easy, especially since it was published online for free. Of course, if you just want to complain something irrelevant about the abstract you’re entitled to it, but IMO that just shows the complainer’s own laziness.

    4) “Only one factor nudges out of the significant range. Look at the last line in table 3. The upper limit of the standard deviation is 0.99 – just a notch away from touching the line of no significance and this is for low-fat fermented dairy. And it’s association, not causation. And it’s about relative, not absolute risk. Do you think that was worth today’s headlines?!”

    Nice attempt to downplay the main findings. Unfortunately, your attempt is kinda lame. Bottom line: low-fat fermented dairy products were clearly associated with smaller risk, even with such small differences in intake. Looking at the upper end of CI is … well, just looking at the upper end: the RR reduction is the key here. Considering that we’re talking about minor differences in just one, very specific food group, the findings are indeed worth reporting.

    And jeez, stating banalities like “correlation-isn’t-causation” doesn’t really matter here, now does it? I take it that you know what kind of study this was? And the difference between AR and RR? Does stating the obvious – that epidemiological studies inevitably have limitations – really change anything?

    Nope.

  11. avatar Robin Dowswell says:

    Thankyou for another useful analysis of dodgy headlines mis-interpreting scientific studies.
    It looks a lot better to be in the high dairy group from the data they present.
    With regard to low fat yoghurt, sometimes all they do is skim off the cream in which case it is what they say it is. At other times sweeteners are added as I found for Danone and Muller Lite yoghurts when I checked them out for the article I wrote last week about yoghurt at: http://www.drdobbin.co.uk/yoghurt.
    The advantage of more fat is of course that you get more exposure to fat soluble vitamins such as A, D, E and K2 which are often consumed below optimal levels by many in the population.

  12. avatar Christopher Vale says:

    I enjoyed reading this post and I’m glad you’re willing to read this stuff on our behalf. The conclusion of no association is definitely unsexy, but not entirely useless when there are still people trying to pin diabetes on a low-carb diet.
    The spinning of low-fat yoghurt as a preventive measure makes a kind of sense for the researchers – if only for future grant money – but what I don’t get is why newspapers all fall for this stuff. It’s almost as if they don’t take health research seriously!

  13. avatar Tom Welsh says:

    I lost any vestigial interest I might have had in the study’s conclusions when I read your words, “…asking me what I ate over the previous year”.

    That works, because we all remember clearly and in full detail what we ate over the previous year! I keep a food diary, but I certainly wouldn’t swear it is deadly accurate. Nor would I care for the core of copying and collating all the details of different foods over a whole year.

    On a (not obviously) related subject, I just read John Kenneth Galbraith’s final book, “On the Economics of Innocent Fraud”. Written when the professor was 95, this 55-page swan song analyzes the many ways in which economists tell the rich and powerful what the latter wish to hear. I see a powerful resemblance to the nutrition advice industry.

  14. avatar Catherine says:

    I said a very rude word when I saw this nonsense, Zoe. Whilst you take the time to explain the various statistics, and what they actually mean, the newspapers and TV bulletins don’t, and I’d like to bet that many of us regular citizens wouldn’t have a clue what most of it really meant. I feel it is deliberately done to bamboozle us, and imply that people with true knowledge of nutrition did this “research”.

  15. avatar Peter Lawton says:

    Why do they bother? Have they nothing better to do with their lives?

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