What Are the Excitotoxins in Diet Soda? A Scientific Breakdown

December 31, 2025 •

3 min read

Millions of people consume diet soda daily, but questions persist about its safety, especially regarding potential excitotoxins. This article dives into what are the excitotoxins in diet soda, focusing on key sweeteners like aspartame and the science behind the controversy.

Quick Summary

Aspartame, a common artificial sweetener in diet soda, contains aspartic acid, which is at the center of the excitotoxin debate. The theory suggests this compound could over-excite and harm neurons, a claim extensively debated in the scientific community.

Key Points

Aspartame is the primary suspect: The excitotoxin debate in diet soda is mainly focused on aspartame, an artificial sweetener that contains aspartic acid.
Aspartic acid is the purported excitotoxin: Aspartame breaks down into aspartic acid, which some researchers believe can act as an excitotoxin and overstimulate neurons.
Caffeine and aspartame may interact: Some theories suggest that the combination of aspartame and caffeine, common in diet sodas, can exacerbate the purported excitotoxic effects.
Regulatory bodies approve, but controversy remains: Despite regulatory approval of sweeteners like aspartame, significant scientific debate and conflicting research results persist regarding their long-term neurological safety.
Newer sweeteners also raise concerns: Recent studies have also highlighted potential neurotoxic and gut health risks associated with other artificial sweeteners like acesulfame potassium (Ace-K) and neotame.
Other health risks are a factor: Beyond excitotoxicity, diet soda has been linked to metabolic issues, altered gut microbiota, and potential confusion of appetite-regulating signals.

Understanding Excitotoxicity

Excitotoxicity is a process where nerve cells (neurons) are damaged or killed by the overstimulation of excitatory neurotransmitters like glutamate and aspartate. These amino acids are crucial for brain functions such as memory and learning under normal conditions. However, excessive amounts can lead to prolonged neuronal firing and eventual cell death, a phenomenon first described in 1969 by Dr. John Olney concerning monosodium glutamate (MSG). In the context of diet soda, the excitotoxin theory primarily focuses on aspartame.

The Role of Aspartame in Diet Soda

Aspartame, an artificial sweetener found in diet sodas under brands like NutraSweet and Equal, is a dipeptide of aspartic acid and phenylalanine. It metabolizes into 40% aspartic acid, 50% phenylalanine, and 10% methanol. Some researchers are concerned that aspartic acid could act as an excitotoxin.

The Breakdown of Aspartame

Aspartic Acid: An excitatory neurotransmitter that some believe, in large amounts from aspartame, could cross the blood-brain barrier and cause neuronal damage through overstimulation, leading to cell death.
Phenylalanine: An essential amino acid that could affect brain neurotransmitters in high doses, particularly for individuals with PKU.
Methanol: Converts to formaldehyde and is considered a neurotoxin. While regulatory bodies view the amount from aspartame as small, critics worry about cumulative effects.

The Aspartame and Caffeine Combination

Some critics suggest the combination of aspartame and caffeine in diet sodas creates a dangerous synergy, intensifying the potential 'excitotoxin' effects and subsequent neuron damage.

The Wider Scientific Debate and Other Sweeteners

The excitotoxin theory regarding aspartame, supported by figures like neurosurgeon Russell Blaylock, remains controversial. Regulatory bodies like the FDA consider aspartame safe based on extensive research. However, the debate persists, with critics citing conflicting studies, industry influence concerns, and limitations in applying animal study results to humans.

Comparison of Common Artificial Sweeteners and Health Concerns


Sweetener	Associated Excitotoxin Concerns	Other Health Concerns	Regulatory Status	Notes
Aspartame	Contains aspartic acid, debated excitotoxin.	Headaches, seizures, potential links to metabolic syndrome, altered gut microbiota.	Approved by FDA, but safety heavily debated by critics.	One of the most studied and controversial sweeteners.
Acesulfame Potassium (Ace-K)	Limited direct excitotoxin links, but affects neurological function in some animal studies.	Altered gut microbiome, potential neurotoxic effects on cognitive function in mice, links to metabolic syndrome.	Approved for use in many countries.	Often used in combination with other sweeteners to improve taste.
Sucralose (Splenda)	Some anecdotal reports link to neurological side effects.	Headaches, dizziness, anxiety. Concerns about heating and potential gut microbiome disruption.	Approved by FDA, some studies show no adverse effects, while others show potential risks.	Very common and much sweeter than sugar.
Neotame	No direct excitotoxin link, but recent studies suggest neurotoxic and gut health risks.	Damage to intestinal lining, gut bacteria disruption, potential link to irritable bowel syndrome and sepsis in recent studies.	Approved for use, but recent research prompts re-evaluation of long-term effects.	Newer, extremely potent sweetener.

Broader Health Impacts of Diet Sodas

Diet soda consumption has been linked to health concerns beyond excitotoxicity, including potential correlations with metabolic syndrome, type 2 diabetes, and cardiovascular issues. Some research suggests diet sodas may disrupt the brain's response to sweetness, possibly increasing cravings for sugary foods and affecting appetite regulation. Artificial sweeteners can also negatively impact the gut microbiome, and phosphoric acid in sodas may be linked to reduced bone mineral density.

Conclusion: Navigating the Controversy

The central question of what are the excitotoxins in diet soda focuses on aspartame and aspartic acid. While the theory of excitotoxicity and neurological damage is debated, with critics citing potential harm and proponents emphasizing regulatory approvals and lack of conclusive evidence, the discussion extends to other artificial sweeteners like neotame and Ace-K and their possible effects on gut health, metabolism, and cognition. The long-term health effects of frequent, high consumption of artificial sweeteners remain an area of ongoing research and debate.

For additional scientific perspectives on artificial sweeteners and their effects, you can review the extensive literature available on platforms like the National Institutes of Health. Review of acesulfame potassium

What to Consider When Choosing Sweeteners

For those concerned about potential excitotoxins or side effects, alternatives like stevia and monk fruit are often considered more natural, though their long-term effects are still being studied. Always check product labels, as many items use a combination of artificial sweeteners. Reviewing the ingredients list is the most reliable way to know what you are consuming.

Frequently Asked Questions

An excitotoxin is a substance, often an amino acid like aspartate or glutamate, that overstimulates nerve cells (neurons) to the point of causing damage or death.

The primary excitotoxin discussed in relation to diet soda is aspartic acid, which is one of the component amino acids of the artificial sweetener aspartame.

Some critics suggest that combining aspartame with the stimulant caffeine can heighten the perceived 'excitotoxin' effect on brain cells, leading to more pronounced overstimulation.

No, there is a significant scientific debate. While some researchers argue for the neurotoxic potential, regulatory bodies like the FDA have historically maintained that sweeteners like aspartame are safe for consumption under specific conditions.

While aspartame is the main focus, other artificial sweeteners like acesulfame potassium (Ace-K) and neotame have also been studied, with some research indicating potential neurological and gut health effects in animal models.

Beyond the excitotoxin theory, diet soda has been linked to metabolic syndrome, gut microbiome disruption, and potential confusion of the brain's hunger signals.

To avoid potential excitotoxins like those debated in diet soda, consumers can opt for alternative sweeteners like stevia or monk fruit, or choose water and other natural, unsweetened beverages.