Sugar and Neurodevelopment: What the Evidence Says for Autism and ADHD

The myth: sugar causes hyperactivity

This one has been tested thoroughly. In careful trials, neither the families nor the researchers knew which children had been given sugar. Those trials, and reviews that combined them, keep finding that sugar does not cause hyperactivity in children, with or without ADHD. The belief lasts mostly because of what parents expect to see. Parents who were told their child had eaten sugar rated the child as more hyperactive, even when the child had really been given a placebo (something with no sugar in it).

Why does the myth stick? Children often eat sugar at busy, exciting events like birthday parties and holidays, where behavior naturally runs higher. That makes sugar look like the cause when it is not.

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What the evidence actually shows

For autistic children

A 2022 study published in Frontiers in Nutrition looked at 107 autistic children and 207 non-autistic children, aged 6–12. What it found:

• Autistic children who had more than two servings of sugary drinks a week had clearly more trouble controlling their emotions, and with planning and organizing, than those who had none. Sugary drinks here means drinks with sugar added, such as soda and sweetened juice drinks.
• The more sugary drinks children had, the more emotional and behavior problems showed up on standard questionnaires.
• Children who drank more milk, by contrast, tended to be kinder and more helpful to others.

A separate 2022 study found that sugary drinks were linked in particular to weaker movement skills in autistic children, such as balance and coordination. This finding is talked about less, but it could matter for everyday living skills.

A 2025 study from Iran compared children with and without autism. In school-age children, eating more carbohydrates overall (starches and sugars, including added sugar) went with more severe autism signs. But it is unclear which causes which. Children who eat a very limited range of foods may eat more processed, sugary foods because of how foods feel, taste or smell to them.

For ADHD

A review that combined many studies, published in Nutrition Research (2020, updated in later reviews), found:

• Children who ate more sugar overall, or drank more sugary drinks, tended to have more ADHD symptoms.
• The link was modest, but it showed up consistently across many studies.
• In one 2023 study, more than 25 g a day of added sugar from drinks went with a higher risk of ADHD symptoms.
• A 2026 Pediatric Research study found that ADHD goes with eating more ultra-processed foods in general: packaged foods made mostly from refined ingredients and additives. Sugar is one part of a wider eating pattern.

These studies show that sugar and ADHD symptoms go together. They do not prove that cutting sugar reduces ADHD symptoms. Trials that change children's diets to test this are underway.

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The gut-brain axis: the most plausible mechanism

The gut-brain axis, meaning the two-way link between the gut and the brain, may be the key here. The best explanation so far for why diet affects behavior in autism and ADHD is probably not sugar acting directly on the brain. It is more likely sugar's effect on the gut microbiome, the mix of bacteria and other tiny organisms living in the gut.

Several reviews (2024–2025) found that autistic children and children with ADHD have a different mix of gut bacteria from non-autistic children without ADHD:

• Autistic children have a different balance between the main groups of gut bacteria, and fewer kinds of bacteria overall.
• ADHD goes with particular patterns of gut bacteria that are linked to attention and impulse control (stopping before acting).

A lot of sugar, especially fructose (a kind of sugar common in sugary drinks), is known to upset the balance of gut bacteria. It feeds the less helpful bacteria, cuts the number of different kinds, and encourages inflammation, the body's irritation response. This may make worse the emotional and behavior difficulties that often come alongside autism and ADHD.

Reviews of probiotics and other treatments aimed at gut bacteria in autism and ADHD show small improvements in behavior and in stomach and bowel symptoms. Probiotics are supplements of helpful bacteria. The improvements are small, but bigger than chance would explain. That is indirect evidence that the gut-brain link matters.

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What the evidence supports:

• Cutting back on sugary drinks is a reasonable step. It makes most sense if your child has a hard time managing big feelings, or with executive function (planning, organizing and getting started on things). The link with sugary drinks in particular is the most consistent finding.
• Eating mostly whole foods, with less ultra-processed food overall, seems to help more than cutting sugar on its own.
• Probiotics show modest evidence of benefit and are low risk. They are worth discussing with your child's pediatrician.

What the evidence does not support:

• Cutting out sugar will not treat autism or ADHD. The core traits, like how your child communicates and what they repeat, do not come from diet.
• Sugar is not responsible for meltdowns, stimming (repeated movements or sounds, like hand-flapping or rocking), or sensitivity to sound, touch, taste and other senses.
• There is no single "autism diet" backed by strong evidence.

A practical note on picky eating: Many autistic children are very sensitive to how food tastes, smells or feels. Ultra-processed, sweeter foods may be among the few foods a child will accept. So go carefully with any change to what your child eats. Making sure they get enough nutrition, and keeping mealtimes calm, matter as much as limiting sugar.