Q. Sometimes I faint after eating a very big meal. Why does this happen? Why do some people faint after hearing bad news?
A. Fainting is the loss of consciousness, or the complete unawareness of the surrounding world and a lack of any response to stimuli. Fainting is caused by an inadequate blood supply to the brain, a condition that can occur for any number of reasons.
Fainting after or even during a big meal is not all that unusual and is caused by the stimulation of the vagus nerve, which is part of the autonomic or automatic nervous system. (This is the system that controls involuntary mechanisms such as blood pressure and the beating of the heart.) when stimulated, the vagus nerve slows the heart rate and causes the blood pressure to fall, both of which impede the flow of blood to the brain. A distended or full stomach can make the vagus nerve fire, which is what results in fainting. There are some people in whom the act of swallowing a large mouth full of food causes a discharge of the vagus nerve, which can cause them to actually pass out at the dinner table. These people may be helped by taking medicine to block the action of the vagus nerve at least a half an hour before they expect to eat. In some cases, it may be necessary to have the vagus nerve cut to relieve symptoms. This is done under general anesthesia in the operating room. Similarly, a severe emotional shock can also cause the vagus nerve to fire, which is why some people faint upon hearing bad or shocking news. In some women, an orgasm can stimulate the vagus nerve and causes fainting.
If you have to stand still on your feet for a long period of time, you may faint due to poor circulation. When the leg muscles move, they “milk” the blood that collects in the veins back to the heart. When the leg muscles are inactive, the blood begins to pool in the lower part of your body, which reduces the blood flow to the brain. If you have to stand in place without movement for a while (like soldiers on guard at ceremonial posts, for example) remember to flex the muscles of your calves every 15 minutes or so to help keep blood from pooling in your legs. Failing to do so is one reason why soldiers faint at their posts.
Fainting can also be a sign of a disorder of the heart rhythm or an arrhythmia in which the heart beats either too fast or too slow. Some hearts beat so rapidly there is little time for them to relax long enough to fill up with enough blood to supply the body adequately. As a result, the brain is deprived of blood and oxygen, and the individual loses consciousness. On the other hand, some hearts beat so slowly that they do not pump enough blood per unit of time to the brain, and the individual faints. In fact, if the heartbeat is too slow, it may be necessary to install an artificial pacemaker in the chest near the heart. A pacemaker is a small, battery-operated unit that produces electrical impulses that stimulates the heart, causing it to contract, thus ensuring the regular flow of blood throughout the body.
Fainting due to stimulation of the vagus nerve is often preceded by nausea, sweating, anxiety, dizziness, and a sense of fading vision. If you feel faint, do not try to get up immediately – this will only further compromise the flow of blood to the brain. Try to lie flat or put your head between your knees to bring more blood to the brain. One of the commonest mistakes would-be rescuers offer an unconscious patient is to pull them to a sitting or even standing position – the worst idea in the world, because gravity further stresses the brain’s blood supply! Loss of feces or urine during fainting, or a bitten tongue, are all signs of a problem more complicated than a simple faint, such as a seizure disorder, and should have the immediate attention of a physician. In fact, any loss of consciousness should be reported to your physician as soon as possible.
Marianne J. Legato, MD, Ph. D. (hon. c.), FACP is an internationally renowned academic, physician, author, lecturer, and pioneer in the field of gender-specific medicine. She is a Professor Emerita of Clinical Medicine at Columbia University College of Physicians & Surgeons and an Adjunct Professor of Medicine at Johns Hopkins Medical School. Dr. Legato is also the Director of the Foundation for Gender-Specific Medicine, which she founded in 2006 as a continuation of her work with The Partnership for Gender-Specific Medicine at Columbia University. She received an honorary PhD from the University of Panama in 2015 for her work on the differences between men and women.
At its core, gender-specific medicine is the science of how normal human biology differs between men and women and how the diagnosis and treatment of disease differs as a function of gender. Dr. Legato’s discoveries and those of her colleagues have led to a personalization of medicine that assists doctors worldwide in understanding the difference in normal function of men and women and in their sex-specific experiences of the same diseases.
She began her work in gender-specific medicine by authoring the first book on women and heart disease, The Female Heart: The Truth About Women and Coronary Artery Disease, which won the Blakeslee Award of the American Heart Association in 1992. Because of this research, the cardiovascular community began to include women in clinical trials affirming the fact that the risk factors, symptoms, and treatment of the same disease can be significantly different between the sexes. Convinced that the sex-specific differences in coronary artery disease were not unique, Dr. Legato began a wide-ranging survey of all medical specialties and in 2004, published the first textbook on gender-specific medicine, The Principles of Gender-Specific Medicine. The second edition appeared in 2010 and the third edition, dedicated to explaining how gender impacts biomedical investigation in the genomic era, won the PROSE Award in Clinical Medicine from the Association of American Publishers in 2018. A fourth edition is forthcoming.
She also founded the first scientific journals publishing new studies in the field, The Journal of Gender-Specific Medicine, and a newer version, Gender Medicine, both listed in the Index Medicus of the National Library of Medicine. She has founded a third peer-reviewed, open access journal, Gender and the Genome, which focuses on the impact of biological sex on technology and its effects on human life.
Dr. Legato is the author of multiple works, including: What Women Need to Know (Simon & Schuster, 1997), Eve’s Rib (Harmony Books, 2002), Why Men Never Remember and Women Never Forget (Rodale, 2005), Why Men Die First (Palgrave, 2008), The International Society for Gender Medicine: History and Highlights (Academic Press, 2017), and most recently, The Plasticity of Sex (Academic Press, 2020). Her books have been translated into 28 languages to date.
As an internationally respected authority on gender medicine, Dr. Legato has chaired symposia and made keynote addresses to world congresses in gender-specific medicine in Berlin, Israel, Italy, Japan, Panama, South Korea, Stockholm, and Vienna. In collaboration with the Menarini Foundation, she is co-chairing a symposium on epigenetics, Sex, Gender and Epigenetics: From Molecule to Bedside, to be held in Spring 2021 in Italy. She maintains one of the only gender-specific private practice in New York City, and she has earned recognition as one of the “Top Doctors in New York.”