5 FDA-approved food additives with brain-damaging effects

By Melissa Sammy, MDLinx
Published February 7, 2020

Key Takeaways

What do the chicken sandwiches from Popeye’s, Chick-fil-A, and McDonald’s all have in common (aside from being delicious, of course)? They all contain monosodium glutamate (MSG), a type of excitatory neurotoxin (excitotoxin) that has been shown to adversely affect the brain.

Excitotoxins are substances, usually amino acids, that overstimulate neuron receptors. Neuron receptors facilitate brain cell communication and, upon excitotoxin exposure, fire more rapidly than normal. This process, if prolonged, can exhaust and weaken the neurons involved, resulting in neuronal death.

So, why are excitotoxins added to food when they pose such a potential threat? They’re usually added to enhance the perception of a food’s flavor. For instance, many people perceive that MSG enhances the savory, umami flavor of certain foods.

But wait—isn’t MSG banned in the United States? This belief is actually a common misconception. Due to emerging evidence supporting the association of MSG with CNS distress, a conscious effort has been made to eliminate the use of MSG across the food industry. However, the excitotoxin is currently approved for public consumption by the FDA—and has been since the 1980s.

Importantly, MSG and other FDA-approved excitotoxins aren’t just found in fast food and takeout. They can be found in food products ranging from potato chips and salad dressing to chicken noodle soup and protein powder.

Here’s a closer look at MSG and other FDA-approved additives that can cause harmful neurological effects:


Perhaps the most notorious excitotoxin, MSG is the salt form of glutamate, or glutamic acid. Glutamate is essential for brain health, but too much can have serious neurological adverse effects. Glutamate has been shown to penetrate the blood-brain barrier and trigger cell death via hyperactivation of the NMDA subtype of Glu receptor. The body naturally produces glutamate when needed to trigger cell death. Too much dietary glutamate, however, can severely disrupt normal cellular function, particularly in the brain.

Questions on MSG’s safety have divided the scientific community for decades. For every study supporting the additive as safe for public consumption, there’s another decrying its potentially harmful effects. For instance, in one study published in The Journal of Headache and Pain, researchers found that individuals who consumed large amounts of MSG were more likely to suffer from headaches and masseter muscle sensitivity. These findings support those from a review in which MSG was found to be a trigger for headache. Yet, in a more recent and larger meta-analysis, researchers found no strong evidence of a causal link between MSG consumption and headache.

The authors of a more recent review offered one possible explanation for these mixed results:

“Although MSG has proven its value as an enhancer of flavour, different studies have hinted at possible toxic effects related to this popular food-additive. These toxic effects include CNS disorder, obesity, disruptions in adipose tissue physiology, hepatic damage, CRS and reproductive malfunctions. These threats might have hitherto been underestimated.”

“MSG is a controversial food-additive used in canned food, crackers, meat, salad dressings, frozen dinners and a myriad of other products. It is found in local supermarkets, restaurants and school cafeterias alike. While MSG probably has huge benefits to the food industry, the ubiquitous use of this food-additive could have negative consequences for public health,” the authors added.


Another excitotoxin that has stirred up similar controversy and debate in the scientific community is aspartame. One of the most popular and widely consumed food additives, aspartame can be found on the ingredient lists of many low-calorie or diet-food products. It is also used as an additive in many medications, especially chewable tablets like Claritin. Numerous studies have emerged over the past few decades either supporting the safety or the harmful health effects of aspartame consumption.

Despite these mixed results, the FDA has maintained an unwavering stance on its approval of aspartame for public consumption: “Aspartame is one of the most exhaustively studied substances in the human food supply, with more than 100 studies supporting its safety. FDA scientists have reviewed scientific data regarding the safety of aspartame in food and concluded that it is safe for the general population under certain conditions.”

Although hundreds of studies support aspartame’s safety, countless others do not. MDLinx previously reported on the harmful cognitive, mental health, and neurological effects associated with aspartame consumption. Notably, high aspartame intake has been shown to induce or exacerbate headaches, and some researchers have linked the artificial sweetener to higher risks of dementia and seizures.


Phenylalanine naturally occurs in many protein-rich foods like milk, eggs, and meat. It is also sold as a dietary supplement and is a component of aspartame. Because phenylalanine can be found in so many food products and medications, the risks of excess consumption and toxicity are high, which can be especially dangerous for people with phenylketonuria (PKU). Individuals with PKU are unable to process phenylalanine properly. Phenylalanine can cause intellectual disabilities, brain damage, and seizures in people with PKU.

“[P]eople with a rare hereditary disease known as [PKU] have a difficult time metabolizing phenylalanine, a component of aspartame, and should control their intake of phenylalanine from all sources, including aspartame. Labels of aspartame-containing foods and beverages must include a statement that informs individuals with PKU that the product contains phenylalanine,” notes the FDA.

If you don’t have PKU, you probably don’t need to worry about adverse effects from phenylalanine. However, because large amounts of aspartame can cause a rapid increase in phenylalanine levels in the brain, you should take certain aspartame-containing medications—such as monoamine oxidase inhibitors, neuroleptics, or medications that contain levodopa—with caution.


Cysteine is an amino acid and food additive that’s used to extend the shelf life of bread and other food products. It’s also used as an artificial flavoring agent. Now for the gross part: Cysteine is created via hydrolysis of human hair and poultry feathers (as well as cow horns and pig bristles). Even worse: High cysteine levels have been associated with the development of neurological disease, including Parkinson disease and Alzheimer disease. So, you might want to think twice when walking down the bread aisle of your local supermarket.


Casein is a protein compound that can be found in cheese at naturally high levels. However, it is also used as a food additive, with its most common form being sodium caseinate. It can be found in margarine, bread, whipped toppings, and bakery glazes. But it can also be found in more health-conscious foods like protein bars, yogurt, and infant formula.

Researchers have shown that high casein intake can disrupt the blood-brain barrier and cause neuroinflammation. Other researchers have suggested that casein may decrease cognitive processing speed.

FDA-approved, safety pending

It’s important to note that while these excitotoxins are approved by the FDA, their approval is based on the quantity in individual food products and their relative risk profile. While most foods and beverages contain these excitotoxins in small amounts, they can quickly accumulate in the body based on a number of factors—including diet, genetics, pre-existing health conditions, body chemistry, and daily medication use. So while that chicken sandwich may be awfully tempting, take a moment to consider the various excitotoxins it may contain—from the MSG in the chicken to the casein in the cheese—and the amount of additives you may have already consumed for the day. How many cups of aspartame-sweetened coffee have you had? Did you take any Advil for that headache that’s been bothering you or any Claritin for your allergies? Food for thought, indeed.  

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