Aspartame. One of those ingredients that sparks immediate debate. Some people swear it’s harmful, others think concerns are overblown. It’s in diet sodas, sugar-free gum, and a ton of other “better-for-you” alternatives, yet it still gets a bad rap.

For those of us who care about brain function -especially with ADHD -it’s worth asking: does aspartame actually affect our focus, mood, or attention? Or is this just another nutrition myth? The internet is full of conflicting takes. Some say it messes with neurotransmitters and causes cognitive issues, while others argue that the dose makes the poison and that there’s no reason to worry. So, let’s dig into the research and see what’s really going on.

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Aspartame and Brain Health: Why the Fear?

After we consume aspartame, it’s metabolized into three components: phenylalanine, aspartic acid, and methanol. The concerns stem from how these may interact with the brain and gut. Some research in rodent studies suggests:

• Methanol can break down into formaldehyde, which in excess amounts can cause oxidative stress and can be cytotoxic.

• Phenylalanine and aspartic acid, both involved in neurotransmitter activity, might decrease dopamine levels in the brain - a key concern for ADHD brains.

• Consuming aspartame could impact the gut microbiome negatively.

Based on the rodent studies, it makes sense why there is this fear about aspartame and brain health. However, it’s important to remember that humans are not rodents, and the doses that the studies give to the rodents are exceptionally high. The rodent studies give us reasoning to ask for appropriate funding to perform studies in humans, and the human studies are the ones we want to focus on when making decisions about our lives.

What Does the Human Research Say?

Here’s where things get interesting:

• A study on dietary patterns found that children with ADHD consume more sugary and artificially flavored beverages. However, correlation doesn’t equal causation—this could be more about dietary habits than a direct effect of aspartame.

• A review of multiple studies found no strong evidence that eliminating aspartame improves ADHD symptoms. In fact, cutting out aspartame made no significant difference in ADHD symptoms.

• Another study concluded that neither sugar nor aspartame negatively affects ADHD behavior in kids - at least at typical dietary levels. This challenges the idea that artificial sweeteners directly contribute to hyperactivity or attention issues.

• Time and time again - like this recent 2024 study - we find that aspartame does not impact the human gut microbiome.

Methanol, Formaldehyde & Aspartame: Should You Be Worried?

A major talking point against aspartame is that it produces methanol, which is then converted into formaldehyde - a known toxin. But here’s what’s often missing from the conversation:

 Our bodies already produce formaldehyde naturally - and in much higher amounts than you’d get from aspartame.

A scientific review estimated that:

• The human body naturally produces 878–1310 mg of formaldehyde per day as part of metabolism.

• The amount of formaldehyde from aspartame metabolism (if consuming the maximum daily intake) would be around 4 mg/kg per day, which is only 0.3–0.4% of what our bodies naturally handle.

So while it’s true that aspartame contributes to formaldehyde exposure, it’s a tiny fraction of what we already produce and clear efficiently. The dose - and our ability to process it - matters.

But Isn’t Formaldehyde a Toxin? Why Does the Body Produce It?

Just like nearly everything with nutrition, most things aren’t “good” or “bad” - it’s the context and the dose that matters. Case in point: formaldehyde isn’t just a toxin; it’s actually essential for life.

✔️ It plays a key role in DNA and amino acid synthesis. Formaldehyde is needed for making purines, which are essential building blocks of DNA and RNA. Without it, cell growth and repair wouldn’t happen.

✔️ It’s involved in neurotransmitter function. The body uses formaldehyde in the metabolism of serotonin, dopamine, and norepinephrine - all critical for mood, focus, and cognitive function.

✔️ It's found in natural foods. Many fruits and vegetables -like apples, pears, and tomatoes - contain small amounts of formaldehyde. The body processes this the same way it does formaldehyde from metabolism or dietary methanol.

So while high levels of inhaled formaldehyde can be harmful, the small amounts produced through normal metabolic processes are necessary and beneficial for health.

So, should we worry about aspartame?

The research is mixed, but there’s no strong evidence that aspartame directly worsens ADHD symptoms for most people. However, individual sensitivity is real—some people notice headaches, mood swings, or brain fog after consuming artificial sweeteners, while others don’t.

One important factor? Context matters. This review of the literature suggests that consuming aspartame with a protein-rich meal could mitigate potential issues. If you’re drinking a diet soda on an empty stomach or alongside a carb-heavy snack, your body may process it differently than if it’s part of a balanced meal.

Additionally, diet patterns as a whole are more impactful than any single ingredient. If someone is consuming a lot of artificial sweeteners, processed foods, and sugar while also restricting nutrient-dense foods, that’s likely to have a greater impact on ADHD symptoms than aspartame alone.

If you feel sensitive to aspartame, trust your own experience. If not, there’s no solid evidence that it directly harms the human brain, body, or gut microbiome. The best approach? Pay attention to your overall diet, prioritize nutrient-rich foods, and experiment to see what makes you feel your best.

Personally? I take a more conservative approach and generally avoid products like diet coke. That being said, if I were to drink a soda, I would choose a sugar-free version rather than a sugar version based on the research on sugar-sweetened beverages and ADHD. Sugar-sweetened beverages and alcohol are a few of the only products that have truly been connected with increasing ADHD symptom severity.

P.S. if you want to know what herbs and supplements are going to actually help your ADHD symptoms, don’t forget to join the Nutrimind Community to get access to the TOP Evidence-backed ADHD Supplements! It’s available in the higher tier at this time ($13/month).

Thanks for reading!

If you have any thoughts, questions, or comments, be sure to shoot me a DM on Instagram @Nutrimindcoach or simply reply to this email. I LOVE hearing from you!

This week on the Nutritional Mental Health Podcast, my friend Steph and I chat about the difficulties of eating with ADHD and some behavioral ways to help. If you want to learn How To Recognize Hunger and Fullness Cues If You're ADHD or Autistic, it’s available on podcast platforms + YouTube. Check out the links below!