I’ve not blogged for a long while but Nina Teicholz seems to be making quite a splash with her latest BMJ piece 1 . The bit that stands out for me – in a piece which is supposed to be showing the weakness of the science behind the 2015 Dietary Guidelines Advisory Committee (DGAC) Scientific Report – is how this piece is used (and the BMJ) to attack recommended diets whilst surreptitiously promoting the idea that low carbohydrate diets are the hard done-by, ignored, always-the-bridesmaid-never-the-bride solution to our problems.
The sophist begins
Another important topic that was insufficiently reviewed is the efficacy of low carbohydrate diets.
Low carbohydrates are certainly an important topic, the DGAC states they have been of “public interest” 2 .
Again, the 2015 committee did not request a NEL systematic review of the literature from the past five years.
“Again” seems to imply a continued refusal to perform a review of the literature. This is of course misleading – a review specifically of low carbohydrate diets was unlikely to be performed in 2015 – because the DGAC is moving away from percentages of fat/carb/protein, and moving towards recommending dietary patterns1 (defined as “the quantities, proportions, variety or combinations of different foods and beverages in diets” 2).
In fact the NEL Systematic Review which Teicholz implies should have been carried for 2015 would have been rather difficult as the DGAC report clearly states that the low carbohydrate studies “generally did not meet the DGAC’s definition of a dietary pattern study unless a full description of the dietary pattern consumed was provided and appropriate methods were used to adjust for the confounding of foods and nutrients”.1
Teicholz in a roll here though, and continues with the DGAC are-ignoring-low-carbohydrate-diets spin
The report says that this was because, after conducting “exploratory searches” of the literature since 2000, the committee could find “only limited evidence [on] low-carbohydrate diets and health, particularly evidence derived from US based populations yet many studies of carbohydrate restriction have been published in peer review journals since 2000, nearly all of which were in US populations.
This is again misleading, as it makes it sound like the DGAC were simply dismissive of the benefits of low carbohydrate diets. However the report states that “The most evidence available focuses on low-carbohydrate diets and body weight. The 2010 DGAC examined the relationship between macronutrient proportion and various body weight outcomes“. The DGAC did in fact carry out a previous systematic review on weight loss, which they lean on in the 2015 report and state there are no further studies which change the conclusions.
This is probably why the 2015 DGAC report specifically identifies “Low-carbohydrate (initially less than 20 g/day carbohydrate) diet without formal prescribed energy restriction but realized energy deficit” as one possible method of weight loss.
So after her attempt to portray the DGAC as ignoring low carbohydrate diets, Teicholz offered some evidence of her own and a counter argument: there are lots of studies since 2000 showing benefit of low carbohydrate diets, you just need to look!
These include nine pilot studies, 11 case studies, 19 observational studies, and at least 74 randomised controlled trials, 32 of which lasted six months or longer (see table C on thebmj.com)”
Table C: Published research on low carbohydrate diets 4 is full of bloat, and many of the studies cited are totally irrelevant to the questions the DGAC were considering. For example the first study on her list: did an inconclusive case study of 5 people with reflux 5 who self administered a low carbohydrate diet really merit formal review for the guidelines?
Do any of the cited studies in Table C provide evidence about the relationship between low carbohydrate dietary patterns and:
- Risk of cardiovascular disease? (question 1)
- Measures of body weight or obesity ? (question 2)
- Risk of type 2 diabetes? (question 3)
- Cancer? (question 4)
- Risk of congenital anomalies? (question 5)
- Risk of neurological and psychological illnesses? (question 6)
- Bone health? (question 7)
Because they were the specific questions which the evidence needs to address, everything else is simply window dressing.
What about some of her other citations, the effect of low carbohydrate diets on epilepsy (numerous), migraines, physical activity, hunger, IBS, and rare conditions like Sturge Weber Syndrome? Are these generally applicable to the population and relevant to answering Questions 1-7?
The task of the DGAC was not to review what Teicholz calls the “many studies of carbohydrate restriction” and dredge for benefits. Does she believe an NEL should be carried out on every medical condition, just to satisfy her that some benefit of her favoured diet has not been cruelly overlooked?
In addition for someone preaching about high quality evidence why is she even listing case studies in Table C anyway? These would fail to meet the standards required for being considered in the NEL systematic review she implies was required. And why does someone who is adamant that conflicts of interest should be avoided produce a table of studies so heavily infected with Atkins Foundation funding?
If only Teicholz was intellectually honest enough to apply the standards to her own work which she demands of others.
Thats not to say she’s doesnt make some valid criticisms
The report provides no documentation of these “exploratory searches,”
With hindsight this was a mistake.
They should have listed the papers found since 2000 on low carbohydrate diets and health in questions 1, 3, 4, 5, 6, 7 and perhaps those on body weight (question 2) since the previous guidelines.
By not doing so, they have allowed Teicholz and the BMJ to create an impression that the guidelines are ad hoc and not based in science and confuse the public further.
Mission accomplished for the headline grabbers and book sellers.
1 The Scientific report guiding the US dietary guidelines: is it scientific? BMJ 2015;351:h4962 http://www.bmj.com/content/351/bmj.h4962
2 Dietary Guidelines Advisory Committee. Scientific report part D: chapter 2. Dietary patterns, foods and nutrients, and health outcomes—continued. http://health.gov/dietaryguidelines/2015-scientific-report/07-chapter-2/d2-2.asp.
3 Dietary Guidelines Advisory Committee. Scientific report part D: chapter 2. Dietary patterns, foods and nutrients, and health outcomes — introduction. http://health.gov/dietaryguidelines/2015-scientific-report/07-chapter-2/
4 The Scientific report guiding the US dietary guidelines: is it scientific? BMJ 2015;351:h4962 http://www.bmj.com/content/bmj/suppl/2015/09/23/bmj.h4962.DC1/teicholzmaster2609.wt3_default.pdf
5 Improvement of gastroesophageal reflux disease after initiation of a low-carbohydrate diet: five brief case reports (PMID:11712463) http://europepmc.org/abstract/med/11712463