We have grown accustomed to the idea that there are good nutrients and bad nutrients. Protein, complex carbohydrates, fiber and essential fats are among the nutrients that are generally considered to be good. Sugars, other simple carbohydrates, and saturated fats are among the nutrients that are generally considered to be bad.
In fact there is no such thing as a bad nutrient-by definition. A nutrient is a chemical compound that the body is able to use for one or more vital functions. In other words, a nutrient is, by definition, a thing that, when ingested, helps the body remain alive. Any nutrient that the body is not able to use for its own benefit but instead harms the body is not a nutrient at all but a poison. Therefore nutrients can only be bad if you consider life itself bad.
How, then, do some nutrients come to be classified as bad? The answer to this question is that there are some nutrients we may eat too much of. By definition, to eat "too much" of a particular nutrient is to eat it in quantities that cause negative health effects. When an over-consumed nutrient becomes associated with health consequences, it is easily forgotten that the essential problem is overconsumption, not properties inherent to the nutrient itself. Thus, what we really mean when we call a nutrient "bad" is that we simply eat too much of it.
Let's look closely at the specific example of sugar. Sugar is arguably the single most vilified nutrient today. Type the word "sugar" into the Google search box and see what happens. I did so and was presented with links to articles with titles such as "The Dangers of Sugar" and "146 Reasons Why Sugar Is Ruining Your Health."
There is no disputing the fact that Americans eat too much sugar, and that eating too much sugar carries significant health consequences. The average American now gets 17 percent of his daily calories from sugar. That's incredible! Undoubtedly, the dramatic increase in overweight and obesity that has paralleled the dramatic increase in sugar consumption over the past 30 years has been caused in part by increased sugar consumption. However, the evidence suggests that it is not sugar per se that has made America fat. Rather, it's simply the fact that we are eating a lot more, and a large portion of those additional calories just happen to be sugar calories.
Scientists have conducted a number of large epidemiological studies designed to connect sugar intake levels with body weight. Believe it or not, the majority of these studies have found no connection. Nor does it appear that sugar causes diabetes, as it is widely believed to do. In one of several studies on sugar intake and diabetes, researchers analyzed data on nearly 39,000 non-diabetic middle-aged women. All of them completed a 131-item food questionnaire, which was used to determine the level of sugar consumption of each. Six years later, there were 918 cases of type 2 diabetes reported. Researchers found no definitive influence of sugar intake on the risk of developing type 2 diabetes.
Not only is sugar not directly to blame for causing some of the health effects it's impugned with, but sugar is also beneficial when consumed appropriately. For example, when consumed after exercise, sugar results in rapid replenishment of muscle glycogen and better performance in the next workout. Indeed, in the right circumstances a can of Coke can literally save your life. How can that be bad?
I'm not suggesting that you should feel free to eat as much sugar as you want. There are two specific ways in which high levels of sugar consumption are problematic. First, a diet that is high in sugary foods is likely to be a diet of caloric excess. Indeed, it is easier to overeat on a high-sugar diet than on a low-sugar diet because sugar provides less satiety (or hunger satisfaction) per calorie than any other type of nutrient. Second, to some extent, the more sugar you eat, the less other stuff you eat. Thus if you eat a lot of sugar you might not get enough of other nutrients such as vitamins, minerals and antioxidant phytonutrients.
There is growing belief among nutrition scientists that under-consumption of micronutrients is perhaps almost as important a contributor to overweight as overconsumption of macronutrients. Dr. Anne-Thea McGill of the University of Auckland recently coined the awkward term "malnubesity" to describe obesity resulting from the combination of overeating and malnourishment that is characteristic of the American diet today, which is also perhaps the most sugary diet in world history.
So it's definitely a good idea to moderate your sugar consumption. But it's wrong to consider sugar inherently bad. And for that matter, it's wrong to consider any nutrient inherently bad. Because if any nutrient is inherently bad, then it is sensible to completely eliminate it from the diet. This type of thinking leads people to do very extreme and stupid things with their eating, like buy Dr. Atkins' New Diet Revolution and subsequently eliminate all of that deadly, deadly, sugar-filled fresh fruit from their diet.