The idea that ADHD (and hyperactivity in general) might be triggered by foods is an old one. Since at least the 1970s, doctors, researchers, and parents have hypothesized that food dyes, additives, sugar, and other dietary components might worsen symptoms for children with this diagnosis. It is a claim that’s understandably of interest to parents, since the idea that changing diet might improve a child’s symptoms without medication is appealing.
Research on this topic has focused on three areas: food dyes and additives; sugar; and an “elimination diet.” A review paper summarizes the data in all three areas. On the first two — food dyes and sugar — the paper concludes that there is no compelling evidence to suggest a link between these foods and ADHD symptoms. Although there are some studies that show correlation, randomized trials do not support this.
However, there is some data on the possible value of an elimination diet. The review paper linked above notes at least seven studies that show improvements in ADHD symptoms with this type of diet. What does that mean? What’s the intervention? And what can we learn from it?
To get to the bottom of this, I want to talk in detail about one of the randomized trials on the question, published in The Lancet in 2011. The structure is similar to other trials, so it gives a good sense of the findings and the limitations. (Even though this paper is from a number of years ago, it still gets significant play online and remains the best in this literature.)
What is the intervention?
The study in The Lancet is a randomized trial. Researchers recruited 100 children who were diagnosed with ADHD and randomized them into two groups. In the control group, parents were given some general advice about healthy diet. In the treatment group, children were put on a version of the “few foods” elimination diet.
It is important to be clear on what this diet is. The few foods diet is a commonly used protocol when doctors are worried about food sensitivities in general. It is a diet that restricts people to a very small number of less-commonly-eaten foods, with the goal of eliminating any possible food triggers. A standard version of the few foods diet would be: a few meats (lamb, turkey, and venison), rice, some vegetables (lettuce, carrots, cauliflower, and beets), pears, and water. In this case, the diet was supplemented with a few other things (potatoes, fruit, and wheat) for some children. Each version was individually designed, to make it as likely as possible that parents would follow the diet.
This diet is extremely restrictive, and long-term use is not feasible for most people. The goal of the diet is to see if there is a response to this extreme level of restriction and then slowly add foods back in.
In this study, the treatment group spent five weeks on the elimination diet. At the end of that period, for children who had responded to the diet by seeing a reduction in their ADHD symptoms, the researchers tried introducing foods to see if symptoms returned.
How are the outcomes measured?
Researchers in the study measured symptoms in various ways, including parent and teacher ratings (based on a survey of teachers at the end of the diet period). The most compelling measure is evaluation by a pediatrician who was not given any information about whether the child was in the treatment or control group.
One of the core concerns with the paper — and everything in this literature — is the placebo effect. Parents obviously know what diet their children are on, and may perceive changes even if they are not there. The masked pediatrician evaluation is therefore very important. However, the pediatric evaluation is based, at least in part, on parental reports (the pediatrician met with the child and also talked to the parents). So it is not immune from the concerns about bias.
I think this paper does about as good a job as possible at objective measurement of outcomes, but it’s very hard to exclude the possibility that there is some placebo bias creeping in.
What are the results?
The elimination diet has a large impact on measured ADHD symptoms. The primary metric is a score on the ADHD Rating Scale, as evaluated by pediatricians — children are given a score on this test, and it is translated to a percentage. Higher percentages mean more symptoms.
Before the intervention, the treatment and control group symptom levels are similar (an average of about 90% for control versus 85% for treatment). After the five-week elimination diet, the control group has a similar score (around 87%), and the treatment group average has dropped to 30%. This is a very large impact.
In the second phase of the trial, some foods were reintroduced to the subset of children who had responded to the treatment. The food introductions were fairly minimal: two foods a week, chosen by the pediatrician. The reintroduction caused a significant relapse in symptoms in the treatment group, returning them to close to baseline. The researchers were interested in whether different types of foods — those with more or less inflammatory potential — had different impacts on relapse. But they didn’t find evidence of that; although some kids had a larger relapse than others, it did not seem to be due to what food was introduced.
Overall, the strict elimination diet seemed to be effective over a period of several weeks, but even very moderate reintroductions of food caused relapse.
What are the limitations of this study?
I noted one limitation above — namely, the fact that it is hard for the evaluation to be fully masked. Separating parent perceptions from reality is tricky.
A second issue is that it is possible that some other changes in parental behavior drive the impacts. Changing diet in such a dramatic way necessitates a lot of parental work, and may mean more attention or other changes. Those could drive the results, and it would be hard to separate from the diet.
A third limitation is that it’s difficult to know the long-term effects of these changes. The diet occurred over a five-week period, and it’s obviously a very challenging diet to hold over the long term. Whether the effects would persist, and whether families could even follow through on the diet in a longer-term way, is an open question. Even in the initial five-week period, 9 of the 50 treatment children left the trial, suggesting that adherence is challenging.
The reality is that a strict elimination diet like this is not likely to be feasible for almost anyone in a long-term way. This is a protocol that some doctors will consider as an experiment if they think foods may be an issue for kids. It is not something that parents should consider on their own, because the extreme nature of the diet makes it hard to ensure that children are getting a balance of vitamins and minerals.
So, can you address ADHD with diet?
A reaction to this work that I have seen on social media is something like: “See, this shows that ADHD is treatable with diet. Make sure you do not give your children ultra-processed foods.”
That is not a realistic reading of this paper, or the literature in general. Studies that have experimented with less sugar or food additives do not see this type of result. The elimination diet here isn’t cutting out a few foods; it’s a very extreme change. Even if we take this result at face value, and do not think it is driven by evaluator effects, it doesn’t suggest that small dietary changes would matter.
This is a case, then, where we should take the result seriously — it is an intervention that some doctors will consider in the case of ADHD if they think there is a food trigger. The idea would be to try this diet and, if it makes things better, reintroduce foods slowly to see if the changes persist. As noted, in this study, for most kids, introducing even a few additional foods caused a relapse, so this is not a solution for everyone, but some doctors do try it.
What this definitely does not suggest is that ADHD is fully caused by diet and would be altered if only your child ate less junk food.
The bottom line
A study followed a group of children put on an extremely restrictive diet to see if there was a reduction in their ADHD symptoms.
The study concluded that putting children on an elimination diet has a large impact on measured ADHD symptoms.
However, this diet is difficult to maintain over a long period of time, which is a clear limitation of the study. It is also hard to avoid bias in reporting.
This study does not suggest that small dietary changes would make a difference in ADHD symptoms and is not a reason to experiment with less sugar or food additives.
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