Monosodium glutamate (MSG) is the sodium salt of glutamic acid, an abundant, naturally occurring amino acid. It functions primarily as a flavor enhancer, providing the savory taste known as umami, which is also found naturally in foods like aged cheese, tomatoes, and seaweed. MSG is produced commercially through the fermentation of starches, sugar cane, or molasses, similar to making yogurt or wine. The U.S. Food and Drug Administration (FDA) generally recognizes MSG as safe (GRAS). Despite this consensus, anecdotal concerns persist regarding adverse reactions, particularly cardiovascular symptoms like heart racing or palpitations.
The Origin of MSG Sensitivity Concerns
Concerns about MSG causing adverse physical reactions gained public attention in the late 1960s. This followed a letter published in a medical journal describing symptoms experienced after eating at Chinese restaurants. This led to the term “Chinese Restaurant Syndrome” (CRS), which included flushing, sweating, chest discomfort, and notably, heart palpitations or a rapid heart rate (tachycardia). These symptoms were speculatively attributed to the monosodium glutamate used in the cuisine.
The term CRS is now considered dated; medical literature refers to these reactions more neutrally as the “MSG symptom complex.” This historical narrative established the connection between MSG and the sensation of a racing heart. The initial reports, though not supported by rigorous evidence, created the foundation for the persistent question of whether the flavor enhancer is a genuine cardiovascular trigger.
Scientific Findings on Heart Rate and MSG
The effect of MSG on heart rate has been extensively investigated using rigorous scientific methods, particularly double-blind, placebo-controlled studies. Researchers have largely failed to replicate adverse reactions, including changes in heart rate, even in individuals who self-identify as sensitive. For example, one study administered high doses of MSG (1.5 to 3.15 grams) to healthy adults before a standardized breakfast.
The frequency of reported sensations was not significantly higher than the frequency reported after receiving a placebo. This suggests that consuming MSG with food negates the potential effects of large doses of free glutamate. While some animal studies using extremely high doses observed minor, temporary fluctuations in heart metrics, these doses far exceed typical human dietary exposure. A typical meal with added MSG contains less than 0.5 grams, whereas doses used to elicit reactions are often 3 grams or more, taken without food. The current scientific consensus indicates that consuming MSG at normal dietary levels does not cause clinical tachycardia or a consistently racing heart.
How the Body Processes Monosodium Glutamate
Monosodium glutamate is a sodium ion attached to the amino acid glutamate. When consumed, MSG rapidly separates into sodium and glutamate in the saliva and stomach. The glutamate released is chemically identical to the glutamate naturally present in protein-rich foods, and the body metabolizes both sources identically.
The vast majority of ingested glutamate is metabolized by the cells lining the gastrointestinal tract, which use it as a primary energy source. More than 95% of dietary glutamate is oxidized or converted into other compounds during this first pass through the gut. This extensive metabolism ensures that only a small, non-toxic fraction enters the general bloodstream. Because the gut effectively processes and utilizes the ingested glutamate, blood levels do not rise significantly enough to trigger acute systemic reactions like a racing heart. Furthermore, glutamate does not easily cross the blood-brain barrier, meaning dietary intake does not impact the brain’s own glutamate levels.
Alternative Explanations for Palpitations
Since evidence does not support MSG as a primary cause of palpitations, the focus shifts to other factors common in large, savory meals.
High Sodium Intake
One significant contributor is the high sodium content often found in restaurant or processed foods. High sodium can cause temporary fluid retention and a slight increase in blood pressure. This change in blood volume can make the heart beat feel more noticeable to sensitive individuals.
Meal Volume and Digestion
The sheer volume of a large meal can also trigger palpitations through mechanical and physiological pathways. A full stomach can expand and press against the diaphragm, a muscle located near the heart, leading to an awareness of the heartbeat. Furthermore, the digestive process requires increased blood flow to the gut, causing the heart to work harder, which some people interpret as a palpitation.
Other Stimulants
Other dietary components frequently consumed alongside MSG-containing foods are known heart rate stimulants. These include caffeine, alcohol, and high amounts of refined carbohydrates, which can lead to blood sugar spikes or nervous system stimulation. Ingredients like tyramine and histamine, found in aged cheeses, fermented products, and cured meats, can also raise blood pressure and trigger palpitations.