Considering Common Health Myths by Christina Badaracco, MPH, RD
Even before the age of social media, maxims about healthy behaviors were spread by word of mouth, marketing campaigns and, sometimes, ill-informed health experts. Today, in our digitally connected world, people continue to struggle to find reliable and accurate guidelines for healthy behaviors as they are bombarded with inconsistent or downright conflicting information. In this Insight, we aim to point out the truth—and untruth—behind six common health tips.
“Drink eight glasses of water per day”
Unless you have been told otherwise by your doctor or dietitian, it’s important to drink a lot of water every day. Drinking enough fluids helps to remove waste through urination and perspiration, balance body temperature, maintain blood volume and more. Most Americans don’t drink nearly enough—US adults consume an average of 39 ounces per day. Further, water intake is lower among older adults and those who have lower incomes and schooling levels, suggesting a wide disparity in this essential behavior—and a need for more education about its importance.
It’s commonly believed that adults should drink eight cups (or 64 fluid ounces) of water each day. A dietitian may calculate needs a few different ways, the simplest of which assumes 1 mL per calorie (note that 1 fl oz equals 29 mL). This comes out to about 68 ounces for someone eating 2,000 calories per day. But more precise recommendations will vary based on a person’s age, sex, body weight and pregnancy or disease status. High heat and exercise that causes perspiration increase needs. Some types of fruits and vegetables can also provide a good source of water (see this Instagram post for more information about water content in vegetables). And other liquids contribute toward meeting the body’s needs; for example, broth in soup, milk in cereal and even coffee are all sources of water. So, not everyone may need eight cups of fluid water every day.
In fact, it is possible to drink too much water. Overhydration can lead to poor sleep quality or the inability to focus at school or work. And at extreme excessive amounts, overhydration can lead to problems such as bladder distention, hyponatremia (when the concentration of the electrolyte sodium in our blood is too low) or even kidney failure. Instead, responding to thirst cues, sipping water throughout the day, drinking water with electrolytes after intense sweating and minimizing highly processed foods high in salt and sugar will help to ensure you drink the appropriate amount of water for your body.
“Exercising enables you to eat whatever you want”
Many athletes and physical fitness buffs have a mentality that they can eat whatever they want as long as they burn it off through exercise. As long as they don’t gain weight, they might not see a reason why they shouldn’t load up on French fries or pizza.
But the food we eat provides so much more than energy for exercise. Each macronutrient and micronutrient in our food has important functions in our body. Loading up on fast food or guzzling protein shakes deprives our body of all of the different nutrients we (as well as our gut microbiota) need to thrive. And the absence of weight gain doesn’t necessarily imply health. Indeed, one can be deficient in nutrients, have poor lab values (such as high LDL cholesterol) and have a higher risk for chronic or infectious diseases, even while exercising intensely and maintaining one’s weight.
Additionally, athletes have varying nutrient needs: they may need more protein to build or repair muscles and water to replenish after perspiration. And since they likely need more total calories, they should still include balanced meals and plenty of nutrient-dense foods. Read this previous Insight for more information about nutrition for athletes.
“Aim for 10,000 steps per day”
Spurred largely by modern fitness trackers, many fitness-minded Americans strive to achieve 10,000 steps (equivalent to almost five miles for an average adult) per day. But this goal actually originated from a marketing campaign, not from healthcare professionals. In 1965, a Japanese company called Yamasa Clock and Instrument Company launched a pedometer called Manpo-kei—which means “10,000 steps-meter” in English. This culture spread first throughout Japan and is now a default goal on myriad fitness trackers and apps worldwide.
While it is important to be physically active every day, this particular threshold is not necessary. A 2019 study by Lee et al. analyzed the association between steps per day and mortality rates among more than 17,000 older women. The authors found that even 4,400 steps (or about 2 miles) per day is associated with significantly reduced mortality; further, benefits level off after 7,500 steps. It has been estimated that the average American walks 4,800 steps each day—slightly higher than the level needed to yield benefit, according to the study. Further, this step goal doesn’t account for other forms of exercise that are also important, such as strength training and yoga, or the speed and level of aerobic exertion. It also doesn’t account for other important health factors, such as metabolic health (e.g., insulin sensitivity) and mental health, that benefit from physical activity.
So, for people who are largely sedentary, walking at least a couple of miles per day can lead to long-term health benefits. It’s important to incorporate both aerobic and non-aerobic activity every week. Finally, moving around the house or yard to do chores is also beneficial for health, even if you’re not carrying your smartphone to track it. Read our past Insight about physical activity for more guidance.
“Follow the five-second rule for food safety”
Many people may have learned to follow the five-second rule as a child, hurrying to pick up a piece of food that just fell to the floor within five seconds and deeming it safe to eat. Surely no harmful pathogens could touch it in five seconds, right?
While it’s true that less contact with a potentially dirty floor (or the bare ground) means less of a chance for bacteria to transfer to the food, that doesn’t mean nothing will touch it in those few seconds. Further, cleaning chemicals, pesticides or other compounds of concern could contact food—especially soft, wet foods—in that short amount of time. In fact, a 2018 study found that:
Bacteria can begin to transfer in less than one second.
Foods with more moisture will be more easily contaminated.
The surface material affects the rate of bacterial transfer, with carpets enabling a slower transfer than tile, stainless steel and wool.
Generally, it’s not worth risking the potential exposure or risk of contamination. People with compromised immune systems, pregnant women and young children are at particular risk. If you are completely sure the floor is clean and the food is relatively dry or hard (e.g., crackers, nuts), it is probably fine to pick it up and eat it. Similarly, a piece of food that can be easily cleaned (e.g., a whole apple) can be rinsed off and is likely fine to eat. But if there is any uncertainty, you are best off adding it to the compost bin.
“Microwaves cause cancer”
Not long after the microwave oven was first made available to consumers in 1955, concerns began to arise about its effects on human health, based on the radiation it produces. Inside microwave ovens, a high-powered vacuum tube creates microwaves that bounce between the metal walls and heat up water molecules in food. In general, such high-energy waves can act as carcinogens by causing mutations in our cells’ DNA. Because of this hazard, the Food and Drug Administration regulates microwave ovens to ensure they are safe for home use; one regulation, for instance, addresses the maximum amount of radiation that can leak more than two inches outside of the microwave. The ovens have been improved over time to leak much less radiation so that, today, microwave ovens pose little risk to users—especially when following proper use protocols, like standing a few feet away while the microwave is on.
Some people have also expressed concern about residual radiation remaining in the food after cooking, making food that was heated (or reheated) in a microwave potentially carcinogenic. However, radiation doesn’t remain in the food once the microwave is off.
It is certainly true that heating in plastic can cause harmful chemicals to leach into food, however, and those chemicals can accumulate and be carcinogenic. Therefore, to minimize overall exposure and risk, it is recommended to microwave only in heat-safe containers—such as glass and ceramic.
“Being cold gives you a cold”
Each year as the days get shorter and the weather gets colder, Americans brace for another cold and flu season. Adults catch an average of two to four colds per year, with young children experiencing up to eight. Given this correlation in timing between the incidence of colds and the colder weather, it has long been thought that spending too much time in the cold can cause one to catch a cold.
In reality, one can only catch a cold by being exposed to one of roughly 200 viruses (particularly rhinovirus) that cause this infection of the upper respiratory tract. Colds are transmitted through an airborne virus or direct contact with infected bodily fluids. There are a few reasons why this is more likely to happen in the winter:
People spend more time inside, in enclosed spaces, which increases the risk of transmission and infection.
Viruses tend to live longer in colder temperatures and lower humidity (as we’ve been recently learning about SARS-CoV-2).
With less exposure to sunlight, Americans tend to be even more deficient in vitamin D in the winter months, inhibiting strong immune responses to viruses.
The best practices to prevent catching a cold any time of year include regularly washing your hands with soap and warm water (especially after being in public spaces), avoiding close contact with people who have a cold (especially during the first few days when they are most infectious) and eating nutrient-dense foods every day to promote resilience.
What’s the best way to learn evidence-based recommendations for healthy behaviors?
Many myths arise from outdated information; stay up to date on the latest nutrition and health science and guidance by reading resources such as the Berkeley Wellness Letter, Harvard Nutrition Source and websites of the Academy of Nutrition and Dietetics and the True Health Initiative.
For written communications, look for valid references from peer-reviewed literature, credentialed nutrition experts and/or leading healthcare institutions.
When reading a story or article based on a study, seek further information about the details of the study to know if the authors’ conclusions are relevant to you. For example, was the study performed on animals (indicating further research is needed to determine impact on humans)? If the study subjects were human, are their characteristics and behaviors similar to yours?
Be especially discerning when an article or presentation is funded by industry; it may be guiding you to certain actions because they support its bottom line.
Althoff T, Sosič R, Hicks JL, King AC, Delp SL, Leskovec J. Large-scale physical activity data reveal worldwide activity inequality. Nature. 2017;547(7663):336-339. https://pubmed.ncbi.nlm.nih.gov/28693034/
“Can Using a Microwave Cause Cancer?” Cancer.Net. www.cancer.net/blog/2021-03/can-using-microwave-cause-cancer. Published March 25, 2021. Accessed April 24, 2021.
“Facts About the Common Cold.” American Lung Association. Updated October 23, 2020. Accessed April 25, 2021. www.lung.org/lung-health-diseases/lung-disease-lookup/influenza/facts-about-the-common-cold
Lee I, Shiroma EJ, Kamada M, Bassett DR, Matthews CE, Buring JE. Association of Step Volume and Intensity With All-Cause Mortality in Older Women. JAMA Intern Med. 2019;179(8):1105–1112. jamanetwork.com/journals/jamainternalmedicine/fullarticle/2734709
Miranda RC, Schaffner DW. Longer Contact Times Increase Cross-Contamination of Enterobacter aerogenes from Surfaces to Food. Applied and Environmental Microbiology. 2016;82(21) 6490-649. aem.asm.org/content/82/21/6490
Rosinger AY, Herrick KA, Wutich AY, Yoder JS, Ogden CL. Disparities in plain, tap and bottled water consumption among US adults: National Health and Nutrition Examination Survey (NHANES) 2007-2014. Public Health Nutr. 2018;21(8):1455-1464. bit.ly/33ZBDKt
Christina Badaracco, MPH, RD
Christina is a registered dietitian and author who aims to improve access to healthy and sustainable food and educate Americans about the connections between food and health. She loves to experiment with healthy recipes in the kitchen and share her creations to inspire others to cook.
Christina completed her dietetic internship at Massachusetts General Hospital and earned her Master of Public Health degree from the University of California, Berkeley. Previously, she graduated with a degree in Ecology and Evolutionary Biology from Princeton University, after conducting her thesis on sustainable agriculture and energy in Kenya. She has done clinical nutrition research at the National Institutes of Health, menu planning and nutrition education at the Oakland Unified School District and communications at the Environmental Protection Agency’s Office of Water. She has also enjoyed contributing to children’s gardens, farmers’ markets and a number of organic farms.