A Balanced Diet

The concept of the importance of eating a balanced diet took on major cultural significance in this country when the U.S. Department of Agriculture released its first Dietary Guidelines for Americans in 1980 — a response to an increase in heart disease amongst Americans in the 1960’s. The Guidelines are updated every five years to incorporate the latest advances in medical and scientific research, based on the recommendations of the 11-member Dietary Guidelines Advisory Committee, a group of widely recognized nutrition and medical experts. The U.S. government directly or indirectly feeds approximately 54 million people daily according to these guidelines — including over 25 million school children. These numbers are not lost on those in the food, agriculture, and diet industries, who are all busy promoting their particular points of view. They work to install members to the committee whose support they can count on, ostensibly in order to ensure that the committee itself has a ‘balanced’ view of diet and nutrition. In such a politically charged environment, what do we end up with? A ‘balanced’ diet indeed, with a little something on everyone’s plate.

While the experts disagree on what constitutes a diet balanced for optimal health, most presume the need for ‘balance’, and the importance of consuming a wide variety of different foods. The guidelines have changed over time, with the recent addition of an emphasis on physical activity to offset caloric consumption. The debate remains largely centered, however, over which foods reside at the top and which languish at the bottom of the food pyramid, rather than the validity of the approach itself.

If one looks to nature for support the entire premise of the need for a balanced diet comes into question. One has to wonder how much of a role the ‘balanced diet’ theory plays in contributing to the morbid obesity epidemic in America today.

Some benefits of a balanced diet, such as the acquisition of essential vitamins, amino acids, and minerals seem relatively irrefutable. However, if a balanced diet confers an adaptive advantage, such an edge appears to have entirely eluded Darwinian forces. Most species have actually evolved specialized dietary preferences, and in many cases have evolved behaviors, anatomy, and physiology to consume a skewed, rather than a balanced diet. An anteater’s long, slender head tapers to a narrow snout, and its tongue can extend up to 24 inches — ideally designed to extract from their nests the ants and termites on which it chiefly feeds. Most Microchiroptera, or “little bats”, have teeth designed for prey, use echolocation to target flying insects, and can scoop up insects in their wings and tail membranes, transferring them to their mouths in mid-flight. On the other hand, Megachiroptera, or “big bats”, sports teeth designed to grind plant parts, use their keen eyesight to spot the fruit they eat from the sky and have long and strong thumbs with curved thumbnail-like claws which they use for climbing around in trees and for gripping fruit.

Indeed, evolution appears to have selected for the ability to use a specialized dietary niche to satisfy all of the body’s needs. Contrary to the assumption that muscle mass correlates with dietary protein, bovines feed largely on plants, yet exhibit ample muscle mass. The unique design of a four-chambered stomach filled with resident microbes allows cows to digest low-quality forage such as grass and then turn it into a high-quality meat and high-protein milk. Wild felines feed almost exclusively on proteins, yet represent paragons of aerobic performance, defying the belief that carbohydrate consumption enhances athletic capacity. The cheetah is the fastest runner on the planet.

Almost no species on earth consumes a balanced diet. While a diet of meat, along with gathered fruits, vegetables, and nuts, was the norm for most of human history, the ratios varied greatly from place to place and season to season. We know for a fact that humans don’t NEED a balanced diet: The Inuit/Eskimo people have lived for generations in great health eating virtually no plant matter, while vegetarians around the world thrive on a meatless diet.

Providing the body with adequate protein, carbohydrate, fat, vitamins, mineral salts and fiber is imperative to proper function. However, the decision to obtain these nutrients through a balanced diet may also carry underappreciated health risks.

Most species that consume selective diets likely rely on taste fatigue — a taste-driven loss of desire to ingest a particular food — to regulate intake. Additionally, a constant taste stimulus will be perceived as decreasing in intensity, while sensitivity to that stimulus is also decreased — the first bite always tastes better than the last. Studies have shown that the more distinct foods (and tastes) that are on a plate, the more the diner will eat. A balanced diet with a variety of foods available at every meal may thus promote overconsumption, as dietary variety subverts taste fatigue.

Diets vary tremendously across cultures and within cultures. Perhaps no country in the world has a greater variety of foods readily and cheaply available than the United States of America: Chinese, Mexican, Italian, Japanese, Indian and the list goes on and on. Would we consume as much if we were restricted even to just one of the above — if we had Icelandic food every single night?

Diets skewed towards particular food groups, such as the Atkins’ high-protein diet, are sometimes espoused, but perhaps health benefits relate less to the balance or skewness of a diet according to taxonomic classifications and more to the qualities of a specific food, independent of its taxonomic classification. Any regimen that restricts the dieter to a limited variety of food likely also benefits from the principle of taste fatigue.

Other popular dietary wisdom such as saving dessert for the end may also contribute to obesity by promoting calorie packing. When we give our children a balanced meal with a variety of foods from all the food groups and make them clean their plates before they can indulge in dessert — a calorie-laden taste sensation they can’t resist no matter how full they are — we get fat kids.

Any discussion of the causes and cures for America’s obesity epidemic must include other important factors, such as a relative disinclination towards exercise. To be sure, there are also many reasons why we might overeat, ranging from supersized portions to depression. However, while a balanced diet is an intuitively appealing notion, with its benefits apparently supported by published data, the reality is that the need for a balanced diet has no clear basis in science. We may just be balancing our way to obesity.

Originally published in The Journal of the Palo Alto Institute in Summer 2009.