Protein-derived chemicals in food

This month I am directing my posts to a discussion of chemicals in our food—primarily those that are added. This week I am focusing on chemicals that are common in proteins. The additives described in Badditives derived from proteins are the artificial sweetener, aspartame, and the flavor enhancer, monosodium glutamate or MSG. Proteins are made up of amino acids. Aspartame is composed of two amino acids—phenylalanine and aspartic acid. MSG is the sodium salt of another amino acid—glutamic acid. Phenylalanine, aspartic acid and glutamic acid are present in all the proteins we get from whole foods such as meat, milk, fish, eggs and soybeans. So what could be so bad about some simple components of proteins? Badditives argues that free amino acids are much more dangerous than those found in proteins, but is that accurate?


Aspartame, also known as NutraSweet, is an artificial sweetener. Phenylalanine is on the left side of the molecule shown above with its characteristic ring structure, and aspartic acid is on the right. The sweetness of this molecule came as a surprise to its discoverer who noticed a sweet taste on his fingers while shuffling papers in his office after working in the lab. His bosses grasped the significance of this accident and turned it into a commercial success as a sugar replacement. I fondly remember my first diet soda sweetened with aspartame at a cafeteria in a shopping mall. I had recently been diagnosed with prediabetes and was looking for a way to cut back on sugar without cutting back on sodas. Despite the designating of sugar as the major contributor to obesity and chronic disease, many food pundits suggest that artificial sweeteners are as dangerous or more dangerous than sugar, based on a few highly publicized studies.The scientific literature, however indicates that artificial sweeteners are not as dangerous as described (1).


Although phenylalanine is an essential amino acid, to certain people it is a toxin. Warning signs on my diet drinks proclaim PHENYLKETONURICS: CONTAINS PHENYLALANINE. What such warnings obscure, however, is that phenylketonurics must be careful when consuming any source of protein. Those living with this rare genetic disorder are restricted to low phenylalanine diets which depend on highly processed (formulated) foods to obtain the necessary amounts of protein. Since all fruits and vegetables contain proteins, even these need to be consumed in moderation. The danger to the general population to the presence of phenylalanine is nonexistent. The absence of phenylalanine in a diet would lead to a protein deficiency without consuming these specially formulated protein foods.

Monosodium glutamate

MSG, or monosodium glutamate as shown above, is the sodium (Na+) salt of glutamic acid, another amino acid. Unlike phenylalanine, aspartic and glutamic acids are not essential for health. In the 1970s MSG was implicated as the causative agent in Chinese Restaurant Syndrome, a flushing sensation that brought on severe headaches and nausea in sensitive individuals who frequented Chinese restaurants. The prevailing theory at the time was that MSG added to wonton and egg-drop soups is rapidly absorbed into the bloodstream from the stomach and travels to the brain analogous to drinking alcohol on an empty stomach. This theory helps explain why free glutamic acid could be more dangerous than glutamic acid in proteins which is released further down in the digestive tract. This explanation has been challenged in a review of subsequent research (2), but the bad reputation of MSG remains. MSG is still prominent in many Asian restaurants as it brings out that unique umami taste that lovers of Asian food desire. I learned from my father that adding MSG to tunafish takes my favorite sandwich to the next level! My family apparently did not have a sensitivity to MSG, but I have friends who do. They steer clear of foods that contain the ingredient.

Gluten is a protein found in breads and other wheat and barley products that is not found in nature. Gluten is an artifact of processing or preparing food at home with wheat ingredients. For example, it is formed as two proteins—glutenin and gliadin—combine when water is added to flour in preparation of making bread. Gluten causes an immune reaction in susceptible individuals who have celiac disease. Celiacs can only prevent the associated digestive symptoms by going on a gluten-free diet. The concept of gluten sensitivity in other people who do not have a clinical case of celiac disease may not be nearly as widespread as suggested in the media (3). It is trendy, however, to avoid gluten without any confirmed symptoms. The problem with gluten-free diets is that they tend to lead to be deficient in certain vitamins and minerals and require supplements. The challenge to prepare and consume a gluten-free diet is difficult as I learned first-hand when I hosted my niece for a week.


Some other substances found in foods derived from proteins or proteins in and of themselves are toxic. One such type of compounds are nitrosamines with one shown above from the amino acid proline. Nitrosamines are also not natural and form when nitrates added to foods react with free amines from proteins in stomach acid. The most common source of added nitrites in foods come from cured meats. Food companies can avoid the shame of declaring nitrates and nitrites on their product labels by using ingredients such as celery salt and celery powder which naturally contain nitrates and nitrites. If an “uncured” bacon or hot dog is that characteristic pink, it contains nitrates and nitrites despite what the product label might say. Whole proteins can also be toxic. For example the botulinum toxin, also known as botox, is a protein and considered the most toxic chemical known to mankind. The toxin responsible for food poisoning by Staphylococcus aureus is also a protein.

True food allergies are reactions to specific proteins. When I was diagnosed with food allergies, I was in denial at first. I underwent the tests and three years of shots to allow me to overcome them. It is much harder to diagnose food sensitivities. Part of the process in treating food allergens is to eliminate all foods with a potential allergen and then add one item back at a time. I had to eliminate any food that contained corn, baker’s yeast, brewer’s yeast and milk from my diet. I was losing weight like crazy. Fortunately, with the help of the shots I was able to add back most of those foods and regain the lost weight. Anyone who suspects a sensitivity to a specific ingredient should eliminate it from the diet and then add a food containing it back a little at a time. If the symptom comes back then we need to learn to live without it. We all need protein, particularly the essential amino acids it contains, but we need to realize that not all proteins or their components are safe. Scare tactics may alert us to potential problems, but each ingredient should be evaluated in the context of the overall diet.

One of my favorite poets from my English literature classes was Alexander Pope who wrote that “A little learning is a dangerous thing.” Too much literature available on food presents “a little learning” as everything you need to know about a specific food, ingredient or additive. It is easy to latch onto simple statements and proclaim them as ultimate truth. As a scientist, I am very wary of anyone who uses “truth” as a weapon in their arguments. Science helps us sort out false claims, but it never settles an issue once and for all. We need to try to get the big picture of any ingredient in our food, both favorable and unfavorable aspects. It is only in that way that we can learn if a questionable ingredient is right for us. Expect more information along this line next week.


(1) Shankar, P., S. Ahuja, and K. Sriram, 2013. Non-nutritive sweeteners: review and update. Nutrition 29:1293-1299.
(2) Freeman, M., 2006. Reconsidering the effects of monosodium glutamate. A literature review. Journal of the Academy of Nurse Practitioners 18:482-486.
(3) Branchia, F., I. Aziz, D. Conte and D.S. Sanders, 2015. Noncoeliac gluten sensitivity: A diagnostic dilemma. Current Opinion in Clinical Nutrition and Metabolic Care 18:508-514. 

Next week: Man-manipulated chemicals in our foods

A special thanks to Dr. Ron Pegg who provided the chemical structures shown in this post.






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