Debunking 10 Nutritional Myths

© Nevit Dilmen, CC BY-SA 3.0, via Wikimedia Commons

Andrew Siegel MD   4/1/2023

Note: Credit to Sophie Egan for some of the myth material that follows. She writes about food, health, and sustainability and is the author of the book: How to Be a Conscious Eater: Making Food Choices That Are Good for You, Others, and the Planet.” 

Myth 1: Humans need to drink 8-12 glasses of water daily.

Reality: Many sources of information (mostly non-medical and of dubious reliability) assert that humans need 8-12 glasses of water daily to stay hydrated and thrive.  Too many people take the 8-12 glass/day rule literally and end up in urologists’ offices complaining of urinary urgency, frequency and often incontinence. Clearly, the 8-12 rule is not appropriate for everyone!  Staying hydrated is important, but it is equally important to avoid being over-hydrated.

Our body demands water “equilibrium,” water intake balancing water losses.  Water needs vary greatly depending upon one’s size, level of physical activity, and ambient temperature.  Water losses are “sensible,” consisting of water losses in the urine and stool, and “insensible,” from skin (evaporation and sweating) and lungs (moisture exhaled).  Remember that water intake derives from solid food as well as beverages, with many foods containing an abundance of water, particularly fruits and vegetables.

The formula that doctors use for determining daily total fluid requirements—useful for hospitalized patients not eating or drinking who depend totally on intravenous fluids—is 1500cc (50 ozs) for the first 20 kg (44 lb.) of weight, and an additional 200cc (7 ozs) for each additional 10 kg (22 lb.) of weight.  So, the daily fluid requirement for a 120 lb. woman is 2000 cc (66 ozs).  The daily requirement for a 165 lb. man is 2600 cc (87 ozs).  It is important to understand that the 66-ounce fluid requirement for the woman and the 87-ounce fluid requirement for the man in this example includes all beverages and food. If one has a very healthy diet with lots of fruits and vegetables, there will obviously be significantly less need for drinking water and other beverages.

The other important factors are ambient temperature and activity level. If you are reading or doing other sedentary activities in a cool room, your water requirements are significantly less than if you are exercising vigorously in 90-degree temperatures.

So, how much water do we need to drink?  Humans are sophisticated and well-engineered “machines” and our bodies let us know when we are hungry, ill, sleepy, and thirsty.  Paying attention to your thirst is one of the best ways of maintaining hydration – drink when your body tells you to.  Also, you can pay attention to your urine color.   If your urine is dark amber in color, you need to drink more as a lighter color is ideal and indicative of satisfactory hydration.

Myth 2: Canned, frozen, and dried fruits and vegetables are always less healthy than the fresh variety.

Reality:  Although canned, frozen, and dried preparations may be less appealing than fresh, the truth of the matter is that fresh is not always best.  The non-fresh formats are typically less expensive, more convenient, readily accessible, incur less risk of contamination, have longer shelf lives, and involve less prep time as they are most often already cleaned, pre-chopped, and cooked.  Frozen veggies and fruits are often more nutritious than fresh because they are harvested at peak ripeness when nutrient levels are highest, then often partially cooked and frozen before they have a chance to deteriorate and lose nutritional integrity.

It is important to read labels carefully concerning added salt, sugar, and other additives that may be present in canned vegetables and which clearly are not healthy. Frozen fruits are generally better than canned fruits because of added sugar in the canned preparations.  Be careful with the calorie count of dried fruits (raisins, prunes, figs, dates, etc.) that are calorie-dense because of the dehydration process.  Frozen fruits are super-convenient for smoothies.

Canned tomatoes are higher in lycopene – the carotenoid antioxidant –than the fresh variety because of the heat process that releases the lycopene.  Frozen peas are picked and frozen at the peak of ripeness, limiting the tendency for the sugar content in peas to convert to starch almost as soon as they are picked.  Frozen spinach is packed much more densely than the fresh spinach, so more spinach in less volume is available and much more punch in terms of nutrients.

Myth 3: All fats are unhealthy.

Reality: Fats are important macronutrients, vital for many bodily functions including providing energy, supporting cellular function, and helping in the absorption of nutrients.  Years ago, fats were vilified and processed foods substituted carbs for fats, contributing to the obesity crisis. Saturated and trans-fats clearly are unhealthy, but monounsaturated and polyunsaturated fats are healthy.  Plant based fats and oils (avocado, olive, nuts, etc.) and fish fats are the healthier fats as opposed to animal and dairy based fats.

Myth 4: In terms of weight loss, the only thing that matters is caloric intake being less than caloric expenditure.

Reality: When caloric intake exceeds caloric burn, weight gain is likely, and the converse is true as well.  However, it’s not that simple, as it is the type of food that is consumed that can drive weight gain.  Highly processed foods are the recipe for weight gain since they trigger the release of insulin and are rapidly absorbed and converted to fat for storage.  For example, compare drinking 8 ozs of orange juice with eating an orange. Orange juice is processed as opposed to the actual orange that contains fiber and phytonutrients.  The liquid juice is essentially “pre-digested” versus the orange that requires work for the body to digest it, and the presence of fiber slows the insulin response and the absorption.  The orange has about half the calories of the juice as well and it so easy to consume more than 8 ozs of OJ but difficult conceptually to imagine eating 3 oranges at one sitting.

Like OJ, all fruit and veggie juices (apple, carrot, grape, etc.) are processed from the original fruit or vegetable and contain high concentrations of sugar while lacking the fiber and phytonutrients that are vital for health.  Like OJ, they are “pre-digested” and rapidly absorbed and converted to fat.  The lack of fiber accelerates the rapid absorption and insulin response.  Eat the intact apple, carrot, grape, etc., as compared with drinking apple juice, carrot juice, grape juice, etc.  The actual fruit or vegetable is so much more filling and healthy. One step worse than fruit juices (that at least originate from healthy fruits) are the processed sweetened beverages including sodas, iced tea, lemonade, etc., that are a recipe for rapid weight gain. 

Myth 5: Cow milk is less healthy than plant milk.

Reality: Plant-based milks (soy, almond, oats, rice, etc.) are not more nutritious than cow’s milk, although they are vegetarian and vegan.  Cow’s milk has much more protein than plant-based milks and many plant-based milks have many added ingredients such as sugar and salt.  Be sure to read the labels carefully.

Myth 6: White potatoes have limited nutritional value and should be avoided.

Reality: Although brightly colored vegetables and fruits are usually chock-full of healthy antioxidants and nutrients, the absence of color does not imply the absence of nutritional value.  Yes, white potatoes do have a high glycemic index and are rapidly absorbed and capable of spiking glucose levels, but when eaten with the skin intact and prepared in a healthy way (baked, boiled, roasted, air fried) have excellent nutritional value, fiber content (average 5 grams in medium-size potato), vitamins, and other phytonutrients.

Myth 7: You cannot obtain sufficient protein intake from a plant-based diet.

Reality: Plant-based foods contain all of the amino acids necessary for sufficient protein intake; however, the ratio of the amino acids is not the same as the ratio in animal-based proteins, so one simply needs to consume a variety of plant-based foods.

Myth 8: Soy-based foods increase the risk of breast cancer.

Reality: Plant estrogens in soy are “isoflavones.”  In scientific studies, isoflavones have been found to stimulate breast tumor growth in laboratory animals; however, this has not been replicated in humans.  Soy-based foods including soy milk, tofu, tempeh, miso, edamame, etc., are replete with high-quality protein, fiber, vitamins, minerals, and other nutrients.

Myth 9: Vegetarian or vegan diets are the healthiest.

Reality:  A vegetarian or vegan diet can be an extremely healthy and cardiac-friendly diet.  However, I know plenty of overweight vegetarians who – although they avoid meats – indulge in plenty of processed and unhealthy foods and have an overall unhealthy diet.  Coca cola, French fries, and chocolate milk shakes are all vegetarian.  Similarly, a vegan diet – although much more restricted than a vegetarian diet – is still susceptible to unhealthy eating habits.  In my humble opinion, the healthiest diets are simply those that avoid processed foods, and are largely – although not necessarily completely – plant based, a “non-processed-atarian” omnivore diet such as the Mediterranean diet.  

Myth 10: Eating meat is unhealthy.

Reality: Aside from ethical and environmental concerns, eating healthy meats in moderation is not unhealthy.  Meat and poultry are rich in protein and provide iron, iodine, zinc, vitamins (particularly B12), and essential fatty acids. Organic and grass-fed beef and lean cuts of poultry are healthiest.  However, excessive red meat consumption is clearly associated with a higher incidence of cardiovascular disease.  Processed meats, often high in salts, additives, flavorings, and preservatives should be avoided.  Cured meats, salami, processed cold cuts, hot dogs, and mystery meats are clearly not on the healthy list.

Wishing you the best of health,

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Dr. Andrew Siegel is a physician and urological surgeon who is board-certified in urology as well as in female pelvic medicine and reconstructive surgery.  He is an Assistant Clinical Professor of Surgery at the Rutgers-New Jersey Medical School and is a Castle Connolly Top Doctor New York Metro AreaInside Jersey Top Doctor and Inside Jersey Top Doctor for Women’s Health. His mission is to “bridge the gap” between the public and the medical community. He is a urologist at New Jersey Urology, one of the largest urology practices in the United States.  He is the co-founder of PelvicRx and Private Gym.  His latest book is Prostate Cancer 20/20: A Practical Guide to Understanding Management Options for Patients and Their Families. 

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Video trailer for Prostate Cancer 20/20

Preview of Prostate Cancer 20/20

Andrew Siegel MD Amazon author page

PROSTATE CANCER 20/20 is now available at Audible, iTunes and Amazon as an audiobook read by the author (just over 6 hours). 

Dr. Siegel’s other books:

THE KEGEL FIX: Recharging Female Pelvic, Sexual, and Urinary Health


MALE PELVIC FITNESS: Optimizing Sexual and Urinary Health

PROMISCUOUS EATING— Understanding and Ending Our Self-Destructive Relationship with Food

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