{"id":5544,"date":"2016-10-03T11:44:46","date_gmt":"2016-10-03T10:44:46","guid":{"rendered":"https:\/\/www.zoeharcombe.com\/?p=5544"},"modified":"2018-10-18T10:58:32","modified_gmt":"2018-10-18T09:58:32","slug":"mediterranean-diet-could-prevent-20000-deaths","status":"publish","type":"post","link":"https:\/\/www.zoeharcombe.com\/2016\/10\/mediterranean-diet-could-prevent-20000-deaths\/","title":{"rendered":"\u201cMediterranean Diet could prevent 20,000 deaths… \u201c"},"content":{"rendered":"
These were the headlines<\/a> that we woke up to on Thursday 29th September 2016. More specifically, it was claimed that a Mediterranean diet could prevent 20,000 deaths in Britain<\/em> each year<\/em>. That\u2019s an important clarification, as we\u2019re all going to die.<\/p>\n The original study can be seen here<\/a> and it\u2019s on open view.<\/p>\n There were three really interesting learnings from this study: i) we get a detailed definition of what researchers think the Mediterranean Diet is (as opposed to what Mediterranean people actually eat); ii) we get a new (and incomprehensible) way of guessing (estimating) the impact of this made up diet on deaths; and iii) we get an example of the new way of reporting studies\/grabbing headlines, which I forecast will end the \u201c20% greater risk \u201c coverage we have suffered to date.<\/p>\n The data source<\/strong><\/p>\n The study is one of personal interest to me, as the data came from the European Prospective Investigation into Cancer study (EPIC) and I\u2019m a member of the EPIC study. This article came from the Norfolk part of the EPIC study (this is called a cohort). The Norfolk cohort included 25,639 men and women, who were aged between 40 and 79 years, when they were recruited into the study (between 1993 and 1997).\u00a0I was some way off this age between 1993 \u2013 1997, so I shouldn\u2019t be part of this particular EPIC cohort. However, it does mean that I am familiar with the EPIC dietary questionnaire and you can see the questionnaire here<\/a>.<\/p>\n I recall completing this questionnaire when I was recruited in the 90s and I\u2019ve had one or two questionnaires since (I can\u2019t remember). I was recruited through the Vegetarian Society, of which I was a member at the time. EPIC wanted more vegetarians to assess, so the Vegetarian Society was a natural recruitment avenue.<\/p>\n Talking of veggies, look at the meat part of the questionnaire on page 3. The questionnaire asks how often we had a \u201cmedium serving\u201d (whatever that is) of each meat on average over the past year (good luck remembering!) There are nine options from \u201cnever\/less than once a month\u201d to \u201c6+ times a day\u201d. That would be easy as a vegetarian i.e. never; not so easy for someone who consumes meat.<\/p>\n Plus, how is the baseline questionnaire balanced with any follow-ups? I was veggie when I first completed the questionnaire, but not veggie at follow-up. If I die now of a heart attack, am I a vegetarian death? Had I been the biggest processed meat consumer in the world in the 1990s and then saw the error of my ways the day after filling in the survey, my heart attack could be attributed to meat consumption, despite 20 years of being veggie.\u00a0That\u2019s how compromised these long term epidemiological studies are.<\/p>\n This study\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/strong><\/p>\n Of the original 25,639 participants in the EPIC Norfolk cohort, some were excluded for not having Food Frequency Questionnaires and\/or for having cardiovascular disease (CVD) at baseline. This left 23,902 participants, with an average age of approximately 59 at baseline (baseline was between 1993 and 1997). CVD cases were examined in 2009 (after an average 12.2 years of follow-up) and CVD deaths were examined in 2013 (after an average 17 years of follow-up). Participants were, on average, 76 years old when CVD deaths were being assessed, so we would expect many to have died.<\/p>\n In fact, not so many people died from CVD during the average 17 years of follow up. To be precise, there were 1,714 CVD deaths per 382,765 person years studied in total. This gave a death rate of 448 per 100,000 people. Well done to the authors for reporting 448 per 100,000 people in the abstract of the article; the absolute death rate is rarely given.<\/p>\n The characteristics of the 23,902 participants were set out in Table 1 and the key differences highlighted in the text. Here\u2019s the key bit, which we\u2019ve seen before: \u201cParticipants with high adherence <\/em>[to the Mediterranean Diet] were less likely to be current smokers, and more likely to be physically active and have a college education and higher social status compared to participants with low adherence<\/em>.\u201d There\u2019s that \u2018healthy people eat healthily\u2019, rather than \u2018eating healthily makes you healthy\u2019 observation, which crops up time and again. Whatever the authors think a Mediterranean Diet is, it is as likely a marker<\/em>, as a maker<\/em>, of a healthy person.<\/p>\n What the article did<\/strong><\/p>\n In simple steps, this is what the article did (because the headlines were about deaths, I\u2019m only going to look at deaths, so as not to confuse numbers with CVD events):<\/p>\n Step 1) Make up a Mediterranean Diet (we\u2019ll come back to this);<\/p>\n Step 2) Assign a score to this made up Mediterranean Diet (we\u2019ll come back to this too);<\/p>\n Step 3) Use highly inaccurate Food Frequency Questionnaires (FFQs) from many years ago (1993-1997 and\/or 1998-2000) to work out how participants scored against this made up Med Diet;<\/p>\n Step 4) Estimate how many CVD deaths were estimated (they do use the estimate word twice in this part of the paper) to be attributable to low (vs. high) adherence to this Mediterranean Diet;<\/p>\n Step 5) Apply this estimate to UK deaths, so that it looks huge and grabs headlines.<\/p>\n That was basically what happened, but there was much fun along the way. Let\u2019s take a quick look at the best bits:<\/p>\n Step 1: Make up a Med Diet<\/strong><\/p>\n If you go to the end of the article<\/a> and look at \u201cAdditional File 1\u201d, this is where we find out how the Mediterranean Diet has been made up. To be fair, four different models of the Med Diet from other articles were used. (The relevant models are fully detailed in references 4, 5, 17 and 28 of the main paper, if you\u2019re interested). The study that forms the major part of the five steps above is the so-called \u201cMediterranean Diet pyramid\u201d, so we\u2019ll stick with the analysis related to this one. (You can find out more about \u201cMediterranean Diet Pyramid\u201d from reference 4 at the end of the paper \u2013 or just Google those words).<\/p>\n Step 2: Assign a score<\/strong><\/p>\n The fabulous Additional File 1 tells us that each participant Food Frequency Questionnaire (FFQ) is assigned a score out of 15 as follows (one point possible per 15 lines):<\/p>\n Table S2: Pyramid based Mediterranean diet score (PyrMDS) scoring criteria<\/strong>.<\/p>\n