A few-foods diet for ADHD: a systematic review of meta-analyses of double-blind, placebo-controlled trials

"... the effect sizes of a few-foods diet are medium to large, justifying implementation of a diagnostic FFD [few-foods diet] in subgroups of children with ADHD [attention-deficit hyperactivity disorder], thus offering innovative treatment opportunities for ADHD."

So said the "Systematic Review of Meta-Analyses of Double-Blind Placebo-Controlled Trials" published by Lidy Pelsser and colleagues [1] (open-access available here) looking at various dietary interventions that have been studied with ADHD in mind. Pelsser, I might add, is a name not completely unfamiliar to this area of investigation as per other research on elimination diets and ADHD (see here).

The few-foods diet mentioned in the opening sentence of this post, could include a few things but Pelsser et al make specific reference to it consisting of "lamb, chicken, potatoes, rice, banana, apple and brassica: foods chosen as they were unlikely to produce an adverse response." You'll perhaps note that there are a few food groups missing from that list of foods, not least the grains (including the gluten protein), dairy products (containing the casein protein) and those processed foods that we all like to enjoy.

The Pelsser paper is an interesting one insofar as their systematically reviewing meta-analyses that were already conducted on dietary intervention(s) for ADHD. Said meta-analyses included in their paper were only allowed in if they meta-analysed double-blind placebo-controlled trials (the gold-standard of clinical trial design). If one assumes that a meta-analysis - where data from different trials is analysed and condensed into a sort of position statement - sits at the top of the evidence-based science hierarchy, the Pelsser study design perhaps sits on top of the top!

Although the FFD receives some welcome scientific backing in the review paper, it was not the only dietary intervention looked at the Pelsser and colleagues. To quote: "six supplement meta-analyses—all investigating the effects of poly-unsaturated fatty acids (PUFA)... —and eight elimination meta-analyses, examining respectively the effects of sugar..., AFC [artificial food colour elimination]..., the Feingold diet..., and the FFD... on ADHD" were reported on. The other interventions did not - for various possible reasons - match up to the research success reported with regards to the current standing of the few-foods diet for ADHD. This included the story on fatty acids for ADHD which has been mentioned previously on this blog (see here for example).

I do not make recommendations on this blog when it comes to intervention and the like for anything. I will however, once again quote Pelsser et al based on their very thorough analysis of the peer-reviewed science in the area of dietary intervention for ADHD: "the effect sizes of a few-foods diet are medium to large, justifying implementation of a diagnostic FFD in subgroups of children with ADHD, thus offering innovative treatment opportunities for ADHD". Also: "FFD research should focus on the mechanism of food in children with ADHD." Their words not mine, and based on some rather credible evidence. I might also add that appropriate dietetic input is a must before anyone heads into the FFD willy-nilly and no, this is not about 'clean eating' or any related fad...

And just before you go, how about casting your eye over the observations made by Alejandra Ríos-Hernández and colleagues [2] and their raising the question of "whether low adherence to a Mediterranean diet might play a role in ADHD development"? Food for thought in the context of the Pelsser data, although perhaps minus the [pregnancy] licorice?

----------

[1] Pelsser LM. et al. Diet and ADHD, Reviewing the Evidence: A Systematic Review of Meta-Analyses of Double-Blind Placebo-Controlled Trials Evaluating the Efficacy of Diet Interventions on the Behavior of Children with ADHD. PLoS One. 2017 Jan 25;12(1):e0169277.

[2] Ríos-Hernández A. et al. The Mediterranean Diet and ADHD in Children and Adolescents. Pediatrics. 2017. Jan 30.

----------

Pelsser LM, Frankena K, Toorman J, & Rodrigues Pereira R (2017). Diet and ADHD, Reviewing the Evidence: A Systematic Review of Meta-Analyses of Double-Blind Placebo-Controlled Trials Evaluating the Efficacy of Diet Interventions on the Behavior of Children with ADHD. PloS one, 12 (1) PMID: 28121994

Food and ADHD: lessons for autism?

I admit that I am a little late in getting to this topic. Late because for quite a while now (years in fact) questions have been raised about a possible link between food, diet and some cases of ADHD (Attention Deficit Hyperactivity Disorder), late because the study published by Pelsser and colleagues which forms the bulk of this post has already been through the blog mill, and late because I had to really think about how to write this post - unlike my others!

First things first. For many years some parents of children diagnosed with ADHD (or ADHD-type symptoms also co-morbid to other things on some occasions) have reported a connection between what their child eats and their child's subsequent behaviour. It was the work of Dr Feingold and a few others who set out the stall that certain types of food preservatives, colours and flavours might be implicated in behaviours associated with ADHD. There has, since the early years of this work, been some significant to-ing and fro-ing about whether Feingold's assertions were correct.

In 2007-2008 two things happened: McCann and colleagues published the results of a tightly controlled study on the effects of food additives on hyperactivity, concluding that certain preservatives and artificial colourings did impact on behaviour. A review by Schonwald in the American Academy of Pediatrics Grand Rounds journal was accompanied by an editorial which all but admitted that following the McCann paper there may be a connection; to quote:  ".. that even we skeptics, who have long doubted parental claims of the effects of various foods on the behavior of their children, admit we might have been wrong".

OK so far? The next "stage" in this saga was the publication a few days back now, of a study from Lidy Pelsser and colleagues (like McCann et al, also published in the Lancet). Pelsser and the group based at the ADHD Research Centre in the Netherlands which includes Jan Buitelaar, have been very, very busy in the area of food and diet in connection to ADHD, publishing results from quite a few trials (see here and here). The result of their most recent study concluded that "a strictly supervised restricted elimination diet is a valuable instrument to assess whether ADHD is induced by food". I am not going to dissect the study here; feel free if you wish to.

So what we have is some good evidence that diet and food could affect some children who present with ADHD or ADHD-type behaviours - emphasis on the "some" children because as we know science is about probability not certainty and we would be hard pressed to say all children show a connection. You may ask then where autism comes into this?

Well, first off, we know that autism and ADHD can occur alongside each other and the association seems quite strong. We also know that some people with autism seem to be affected by diet; whether as a consequence of co-morbid conditions such as coeliac disease or through less well-defined connections. The types of diet most commonly linked with autism are those excluding gluten- and casein, but there are several more being quite widely discussed. I will stay with the GFCF diet because that's what I know ('a cobbler should stick to his last' and all that).

The most recent Pelsser study described their diet (at least in the first phase of their study) as consisting of a few foods; just rice, meat, vegetables, pears and water. Notice that a few things are missing from this diet including our old friends gluten and casein (although I believe small amounts of wheat were included on specific days for some participants for RDA reasons). When however you compare the Pelsser results on ADHD with some of the data from autism, a few "similarities" start to occur. For example, during our most recent 2-year ScanBrit trial of the GFCF diet for autism we included a few measures outside of autism aimed at examining ADHD-type behaviours (for those of you interested it was the ADHD-IV scale by DuPaul and Power) given the previous suggestions that such areas of functioning may be affected by diet. What we found and reported on was that hyperactivity and inattention sub-domains seemed to indicate some "group" reduction following intervention.

Fair enough I hear you say, a non-blinded study showing that ADHD-type behaviours presented by children with autism "seemed" to show a significant group reduction effect after diet? One study: it shows nothing. Well not quite. Another recent trial by Cynthia Johnson and colleagues also looked at the effects of a GFCF diet on children with autism. Similar to ScanBrit, the trial was randomised but not blinded and compared a GFCF diet to a healthy low sugar diet for autism over the course of 3 months. Their results: overall no significant gains on the GFCF diet vs. the healthy low sugar diet but reading the full-text to their paper, an interesting finding: a significant reduction in ADHD behaviours for the GFCF group (p = 0.043) (Table 5) which were also examined during their study.

The skeptic in me says OK possibly a fluke event in both cases; the reduction in ADHD-type behaviours could be down to the study design (non-blinded), other things the participants were doing at the time of study or merely because more attention was given to them as a consequence of being "studied". A small, little, tiny voice is however telling me: "mmm, this is interesting, does this need a little more study?" I will let you answer that question yourselves.