red and black background pattern

Issues in Every Forkful

By Melissa Hendricks

At meal times, do your internal monologues sound like this?

How about a nice piece of buttered toast?
      No, can’t do that. Too much saturated fat.
Okay, use margarine.
      No way. Not those deadly trans-fatty acids.
Well then, just a plain bagel.
      Are you kidding? Its glycemic index will send your blood sugar through the roof. 
Oh, forget breakfast. Let’s just take a 30-minute walk, like the Surgeon General recommended. 
      Better make that a full 60! 

Just when you find something to eat that the experts say is okay, the experts, it seems, change their minds. Why is eating so darn confusing? 

One reason could be that—with more than half of the American population overweight—many people are more interested in dieting than in eating a healthy diet, and there are zillions of “experts” out there promoting their own version of the “right” and “wrong” foods for weight loss. So the contentious debate over the best diet naturally overshadows the discourse on a healthy diet. “It’s a field that is so subject to fashion and a quick buck, unfortunately,” says weight management expert Lawrence Cheskin, an associate professor at the School’s Center for Human Nutrition. 

Another complicating factor: Many different interest groups have their agendas about food, some of which spring from science and some from prejudice, says Benjamin Caballero, director of the School’s Center for Human Nutrition. As a member of the Institute of Medicine’s (IOM) Food and Nutrition Board, Caballero has heard arguments that animal protein adversely affects health. But in reading thousands of scientific papers, he and his colleagues found no evidence that the protein in meat confers more health problems than protein from plant sources. 

Of course, science itself has contributed to the complexity of eating right. To illustrate this point, Caballero goes to a crammed shelf in his office at the School and retrieves three books. He places the first one on a coffee table. The slender volume contains the Recommended Dietary Allowances (RDAs) as issued in 1968, by the IOM’s Food and Nutrition Board. Next, Caballero sets down another, slightly larger book, the 180-page RDAs from 1989. Finally, he hoists onto the table a book the size of a city Yellow Pages. “This is one-seventh of the Food and Nutrition Board’s current report,” he declares, a compendium of books that the IOM began publishing in 1998. In compiling the report, board members reviewed more than 7,000 scientific references.

In its latest update of the RDA, the Food and Nutrition Board issued a broad—and more complex—set of benchmarks called the Dietary Reference Intakes (DRI). The latest report examines minimum nutrient requirements, as well as nutritional factors that might enhance health and prevent chronic disease, and the ill effects of getting too much of a good thing. A sampling:

Fat — Previously, the Board recommended that fat comprise no more than 30 percent of the diet. (Despite what critics have charged, says Caballero, “We never recommended a low-fat diet.”) The latest recommendation: Anywhere between 20 to 35 percent fat is healthy. 

Why the change? The 30 percent maximum figure, says Caballero, “was somewhat arbitrary.” The latest recommendation is based on voluminous clinical and epidemiological studies, including research on Europeans who eat a Mediterranean diet. “They consume 35 to 36 percent fat, and have some of the lowest rates of cardiovascular disease in the world,” he explains.

The report for the first time also distinguishes among different types of fats. People should include mono-unsaturated and polyunsaturated fats in their diets, and shy away from saturated fats and trans-fatty acids, which raise levels of “bad” cholesterol. Trans-fats occur in partially hydrogenated vegetable oils, found in many cookies, crackers, and fast foods.

For the first time, the Board defined minimum requirements for two polyunsaturated fatty acids: omega-3 fatty acid (alpha-linolenic) and omega-6 fatty acid (linoleic), which can be found in fish, milk, and safflower, corn, soybean, and flaxseed oils.

Carbohydrates — Carbs should make up 45 to 65 percent of the calories an adult consumes—up slightly from what the Board recommended in its previous report. Try to choose complex carbohydrates like whole wheat bread and brown rice, advises Caballero. 

Fiber — The Board issued its first recommendation on fiber. The bottom line: Americans need to eat more fiber, found in foods such as fruit, vegetables, legumes, and cereal bran. There is strong evidence for the protection fiber offers against heart disease. 

Exercise — To prevent disease and maintain a healthy weight, adults should exercise for 60 minutes per day to avoid weight gain, according to the Food and Nutrition Board. That recommendation was based on studies that analyzed data from more than 100 investigators who used a precise method of calculating calories burned known as the doubly labeled water technique, says Caballero, who chaired the board panel that reviewed those studies.

A person can accumulate activity throughout the day to arrive at the hour-long sum of moderately strenuous exercise, notes Caballero. 

For example, an office worker might take the stairs instead of the elevator, go for a 15 minute walk at lunchtime, and vacuum the house after work to arrive at the daily goal.

The Surgeon General had previously recommended just 30 minutes of exercise per day. That recommendation grew out of epidemiological studies, while the Food and Nutrition Board relied on a precise clinical tool for measuring calories burned. Both conclusions still hold. Sixty minutes of exercise will help you avoid weight gain, but even 30 minutes will help tone your body and cut down on your disease risk.

Food pyramid — Constructing the food pyramid is the job of the U.S. Department of Agriculture, not the Food and Nutrition Board (although the USDA consults the Board’s findings to craft the pyramid). Some nutrition experts, including Caballero, believe the pyramid is fine as is. But critics say it fails in several regards: It does not distinguish between refined and unrefined carbohydrates; it lumps all fats into one category. Several medical experts and organizations offer alternative food pyramids.