The popular concept of the term “healthy diet” has become rather blurred and misunderstood during the past few decades.

First, a healthy diet should provide all of the 40-some essential nutrients in adequate amounts. This is why traditional diet recommendations have included all food groups, each with its nutrient strengths and weaknesses. This also is why school lunches have offered foods from all the key food groups in hopes that students will eat adequate amounts of everything served and meet their nutrient needs.

However, in 1977 when the first “Dietary Goals for the United States” were published, the focus of diet recommendations shifted from meeting nutrient needs to reducing chronic disease risk. This emphasized consuming more fruits, vegetables and whole grains and less meat, milk fat, eggs, sugar and salt. Following publication of the “Goals,” Dr. Alfred E. Harper, a University of Wisconsin nutrition professor, repeatedly pointed out that these recommendations ignored that life expectancy had increased by 20 years since 1900 and the age-related incidence of heart disease and stroke had decreased. However, the diet recommended by the “Goals” completely ignored the major nutrient deficiency in the U.S.: iron deficiency.

Question: What problems are most likely to occur from lack of iron?

Answer: In addition to anemia and the fatigue caused by iron deficiency, this single deficiency can adversely affect sleep, moods and the liver’s capacity to handle toxins, among a multitude of other health problems. The decreased detox capacity of the liver can be extremely problematic because many drugs and natural toxins in food become more toxic to the body. Also, iron deficiency causes the body to absorb excessive amounts of potentially toxic trace minerals such as lead, aluminum and manganese. Diets with limited iron also are generally low in zinc. Zinc deficiency decreases the ability to learn, depresses immune function and prevents normal sexual maturation. Both iron and zinc are absorbed more efficiently from animal foods.

Q: What other essential nutrient problems can occur when the diet is primarily plant-based?

A: Protein can become inadequate in a plant-based diet — especially when calorie intake is low. The body adapts to a low protein intake by sacrificing its own protein, primarily from muscle tissue. When protein reserves in the body run too low, the immune system can become compromised, making it more difficult for the body to avoid viruses and handle infections. Inadequate protein also compromises intestinal health in ways that can increase the risk of developing food allergies.

The amount of protein needed is highly dependent on body weight. Daily protein needs are expressed in grams of dietary protein needed per pound of body weight. For example, the protein Recommended Dietary Allowance, or RDA, for a healthy person is about 36 grams for a 100-pound person and 73 grams for a 200-pound person. However, Colin Wills’ recent University of Hawaii master’s thesis using national data shows that individuals’ BMI and body fat were lower when they were consuming about double the RDA for protein.

It requires only about 8 calories of food to get a gram of protein from lean meat, fish, poultry and eggs. However, it requires three to four times as many calories to get a gram of lower-quality protein from beans, grains and nuts.

Our next column will address nutrient excesses and related health problems.