Nutrition is a science founded in biology, physiology and chemistry. Nutrition is not a religion, it is not an ideology, nor is it a lifestyle. Clearly, religious, philosophical and lifestyle concerns affect how people choose to eat. However, to stay physically and mentally healthy, we all need to consume an adequate supply of over three dozen essential nutrients.

Fortunately, a healthy human body is surprisingly tolerant of dietary extremes for fairly long periods of time. This, however, depends on the nutrient and how long its deficiency takes to develop. When someone has been eating a slightly deficient diet for a long time, the dietary cause of a health problem often is not even considered and can be difficult to diagnose. Sadly, as a person begins to experience fatigue or other health problems, they may actually become stricter in their dietary choices, making the nutrient deficiency and subsequent symptoms worse.

There are a growing number of true believers promoting overly restrictive or extreme diets for laudable philosophical and/or environmental reasons without even considering step one in nutrition science — meeting essential nutrient needs. Promotion of these diets includes everything from fear tactics to guilt and a good helping of misinformation.

Question: Which diets cause health problems?

Answer: Any diet that is deficient in one or more of the essential nutrients will cause problems. At one extreme, this could be a meat, rice and soda diet. At the other extreme it could be a vegetarian, vegan or raw-food type of diet that also overly limits the variety of foods available and may even provide inadequate calories. Any eating style that limits food variety is risky.

Q: Can an extreme diet that seems to work well for one person cause problems for someone else?

A: Yes. Nutrient requirements vary slightly from one person to another. The Recommended Dietary Allowances for nutrients published by the Institute of Medicine attempt to allow for this variability. However, these recommendations are made for the average healthy person consuming a diet containing all of the major food groups, including meat and dairy. Many of today’s so-called "healthy" diets are limited in certain nutrients or may even exceed the safe upper levels for other essential nutrients. Also, too much of some "healthy" foods may decrease the absorption of certain essential nutrients.

Men and women also have some significant differences in nutrient requirements. The most significant discrepancy is iron needs. Women, during their reproductive years, require more than twice as much iron as men. However, the recommendation of 18 mg of iron per day increases to 33 mg of iron if a woman chooses to consume a vegetarian or vegan diet.

A diet that promotes health when plenty of food is consumed may become inadequate when calorie needs decline (but nutrient needs do not). This often is seen with aging.

Three commonly used tactics used to convert people to certain eating styles are guilt about the environment, ethics of consuming animals and fear of so-called poisons in our foods. Should we care about food safety? Of course!

However, microbial food contamination is the greatest risk — as currently illustrated by the E. coli problem at Chipotle Mexican Grill restaurants. But on the whole, our food is safer than it has ever been.

So, before you change your eating style, make sure there will be adequate variety across and/or within the key food groups. As a reminder, those food groups are protein foods (meats, fish, eggs, beans and nuts), dairy foods, grains, fruits and vegetables. 

Alan Titchenal, Ph.D., C.N.S., and Joannie Dobbs, Ph.D., C.N.S., are nutritionists in the Department of Human Nutrition, Food and Animal Sciences, College of Tropical Agriculture and Human Resources, University of Hawaii-Manoa. Dobbs also works with University Health Services.