[Viewpoint] Diet debacle
Two seemingly benign nutritional maxims are at the root of all dietary evil: A calorie is a calorie, and You are what you eat. Both ideas are now so entrenched in public consciousness that they have become virtually unassailable. As a result, the food industry, aided and abetted by ostensibly well-meaning scientists and politicians, has afflicted humankind with the plague of chronic metabolic disease, which threatens to bankrupt health care worldwide.
The United States currently spends $147 billion on obesity-related health care annually. Previously, one could have argued that these were affluent countries’ diseases, but the United Nations announced last year that chronic metabolic disease (including diabetes, heart disease, cancer and dementia) is a bigger threat to the developing world than is infectious disease, including HIV.
These two nutritional maxims give credence to the food industry’s self-serving corollaries: If a calorie is a calorie, then any food can be part of a balanced diet; and, if we are what we eat, then everyone chooses what they eat. Again, both are misleading.
If one’s weight really is a matter of personal responsibility, how can we explain toddler obesity? Indeed, the U.S. has an obesity epidemic in six-month-olds. They don’t diet or exercise. Conversely, up to 40 percent of normal-weight people have chronic metabolic disease. Something else is going on.
Consider the following diets: Atkins (all fat and no carbohydrates); traditional Japanese (all carbohydrates and little fat); and Ornish (even less fat and carbohydrates with lots of fiber). All three help to maintain, and in some cases even improve, metabolic health, because the liver has to deal with only one energy source at a time.
That is how human bodies are designed to metabolize food. Our hunter ancestors ate fat, which was transported to the liver and broken down by the lipolytic pathway to deliver fatty acids to the mitochondria (the subcellular structures that burn food to create energy). On the occasion of a big kill, any excess dietary fatty acids were packaged into low-density lipoproteins and transported out of the liver to be stored in peripheral fat tissue. As a result, our forebears’ livers stayed healthy.
Meanwhile, our gatherer ancestors ate carbohydrates (polymers of glucose), which was also transported to the liver, via the glycolytic pathway, and broken down for energy. Any excess glucose stimulated the pancreas to release insulin, which transported glucose into peripheral fat tissue, and which also caused the liver to store glucose as glycogen (liver starch). So their livers also stayed healthy.
And nature did its part by supplying all naturally occurring foodstuffs with either fat or carbohydrate as the energy source, not both. Even fatty fruits — coconut, olives, avocados — are low in carbohydrate.
Prior to 1900, Americans consumed less than 30 grams of sugar per day, or about 6 percent of total calories. In 1977, it was 75 grams/day, and in 1994, up to 110 grams/day. Currently, adolescents average 150 grams/day (roughly 30 percent of total calories) — a five-fold increase in one century, and a two-fold increase in a generation. In the past 50 years, consumption of sugar has also doubled worldwide. Worse yet, other than the ephemeral pleasure that it provides, there is not a single biochemical process that requires dietary fructose; it is a vestigial nutrient, left over from the evolutionary differentiation between plants and animals.
It is therefore clear that a calorie is not a calorie. Fats, carbohydrates, fructose, and glucose are all metabolized differently in the body.
Furthermore, you are what you do with what you eat. Combining fat and carbohydrate places high demands on the metabolic process. And adding sugar is particularly egregious.
Indeed, while food companies would have you believe that sugar can be part of a balanced diet, the bottom line is that they have created an unbalanced one. Of the 600,000 food items available in the U.S., 80 percent are laced with added sugar. And this brings us back to those obese toddlers.
The fructose content of a soft drink is 5.3 percent. Of course, many parents might refuse to give soft drinks to their children, but the fructose content of soy formula is 5.1 percent, and 6 percent for juice.
We have a long way to go to debunk dangerous nutritional dogmas. Until we do, we will make little headway in reversing an imminent medical and economic disaster.
Copyright: Project Syndicate, 2012.
*The author is a professor of pediatrics in the division of endocrinology at the University of California, San Francisco.
by Robert Lustig