Aspartame is one of the most widely used artificial sweeteners in the world, but there are conflicting views on its safety and health effects.
Key Facts:
- Aspartame is about 200 times sweeter than sugar but contains minimal calories. It is commonly used in diet sodas and other sugar-free products.
- When digested, aspartame breaks down into phenylalanine, aspartic acid, and methanol. High levels of these metabolites may be toxic.
- Studies suggest links between aspartame and increased risk for mood disorders, neurodegenerative diseases, and poor brain development in fetuses. However, current evidence is not conclusive.
- People with the genetic disorder phenylketonuria (PKU) cannot properly metabolize phenylalanine and need to strictly limit aspartame consumption.
A Popular Artificial Sweetener with Uncertain Effects
Aspartame is an intensely sweet artificial sweetener that is widely used as a sugar substitute in foods and beverages.
First discovered in 1965, aspartame was approved for use in food products in the 1980s and quickly gained popularity as a zero-calorie sweetener.
Today, it is found in thousands of consumer products worldwide, especially diet sodas.
While aspartame tastes up to 200 times sweeter than sucrose (table sugar), it contains minimal calories because the body does not metabolize it.
When digested, aspartame breaks down into three components – phenylalanine, aspartic acid, and methanol.
At normal intake levels, these metabolites are safe.
However, some scientists believe that high consumption of aspartame could lead to dangerous spikes in metabolites that impact the brain and nervous system.
How Aspartame Breaks Down in the Body
When consumed, aspartame undergoes metabolism in the gastrointestinal tract.
Enzymes called esterases break the molecule down into its core components:
- Phenylalanine – an essential amino acid and building block for proteins. Makes up 50% of aspartame.
- Aspartic acid – a common amino acid. 40% of aspartame.
- Methanol – the simplest form of alcohol. 10% of aspartame.
Methanol then gets converted into formaldehyde and formic acid through oxidation.
While small amounts of these metabolites are not an issue, high doses have been shown to cause adverse effects in animal studies:
- Methanol can be neurotoxic and poisonous. Its conversion into formaldehyde and formic acid produces free radicals that can damage cells.
- Phenylalanine can inhibit the synthesis of neurotransmitters like dopamine and serotonin when present in excess. This may impact mood regulation.
- Aspartic acid acts as an excitatory neurotransmitter. Too much can overstimulate neurons and disrupt their function.
Concerns Around Aspartame & Brain Health
The breakdown of aspartame raises concerns that high consumption over long periods could harm the brain and nervous system.
Behavioral Disorders
A number of studies indicate aspartame and its metabolites may negatively impact mood and cognition:
- Increased phenylalanine can reduce dopamine and serotonin levels, potentially contributing to depression.
- Excess aspartic acid overstimulates neurons, which may lead to issues like headaches or impaired memory retention.
- Aspartame appears to raise cortisol levels, which are associated with depression and anxiety.
- Rodent studies show altered behavior and endocrine responses after long-term aspartame exposure.
While more research is needed, these findings suggest aspartame could exacerbate or increase risk for certain behavioral disorders.
Neurodegeneration
The metabolites of aspartame generate oxidative stress and free radicals that can damage neurons over time.
Animal studies show long-term aspartame consumption may contribute to:
- Changes in neuron structure, including shrinkage and irregular thickening.
- Degeneration of brain regions like the hippocampus that are vital for cognition.
- Reduced acetylcholinesterase activity in the brain, which plays roles in learning and memory.
However, the doses given to animal subjects are typically much higher than normal human consumption.
More studies are required to assess neurodegenerative risk.
Effects on Fetal and Child Development
Some research indicates maternal aspartame intake may have detrimental effects on babies during gestation or childhood:
- Increased obesity, glucose intolerance, and altered gut microbiota in animal offspring. Effects more pronounced in males.
- Possible heightened risk for premature birth, allergies, and early puberty in young girls.
- Methanol passing through the placenta may impact brain development.
However, human studies have not found adverse effects from aspartame at typical consumption levels during pregnancy.
The evidence is currently limited and mixed.
Links to Brain Cancer Appear Unlikely
Early fears arose that aspartame’s methanol metabolite could cause cancers, including brain tumors.
However, decades of research have not found clear evidence linking aspartame to higher cancer rates in humans.
While a few animal studies have found increased expression of oncogenes and possible slowed apoptosis, the doses far exceeded human intake.
Overall the cancer risk appears low, but more long-term studies are warranted.
Aspartame and Autism
Some advocacy groups claim aspartame consumption during pregnancy increases the likelihood of autism spectrum disorder (ASD).
The hypothesized mechanisms include:
- Methanol crossing the placenta and impacting fetal brain development.
- Increased oxidative stress affecting the developing brain.
But while maternal methanol intake correlates with higher ASD rates, no research proves aspartame specifically causes autism.
The spike in ASD diagnoses also coincided with changing diagnostic criteria.
At this time, there is insufficient evidence to conclude aspartame contributes to autism risk.
Avoiding Aspartame with Phenylketonuria
Individuals with phenylketonuria (PKU) should strictly limit their aspartame consumption due to the phenylalanine metabolite.
PKU patients lack an enzyme needed to properly process phenylalanine, causing it to accumulate to toxic levels in the body and brain.
Even single servings of aspartame can significantly spike phenylalanine levels in those with PKU.
Patients need to carefully monitor diet and nutrient intake to prevent severe developmental delays.
All products containing aspartame must carry a PKU warning label.
Controversy Continues Due to Lack of Clear Human Data
Animal studies link aspartame metabolites to oxidative damage, hormonal dysfunction, cancer markers, and neurobehavioral issues.
However, human studies remain limited and inconclusive.
There is particular concern around fetal and childhood exposure to aspartame, but current evidence does not clearly establish toxicity or adverse effects at typical doses.
Aspartame consumption appears to carry little risk for most healthy adults at moderate intake levels.
But the long-term impacts of higher daily consumption require further research.
People with PKU need to avoid aspartame due to the phenylalanine content.
Products should always contain clear PKU warnings.
While the evidence is conflicting and unclear, there are enough red flags around aspartame to warrant caution and further study.
More rigorous controlled human trials are needed to truly assess safety.
References
- Study: Aspartame – True or False? Narrative Review of Safety Analysis of General Use in Products
- Authors: Kamila Czarnecka et al. (2021)
