But considered in isolation and spun into a narrative about the evils of carbs, these partial truths end up misleading rather than informing.
Taubes correctly points out that many early researchers, in the way they crafted their studies and reported their findings, were confusing the three main hypotheses for the causes of obesity and related illnesses: excess calories, excess fat, and excess carbs. According to the first hypothesis—by far the most common—we gain weight because we ingest more calories than we burn. This is the hypothesis I mentioned earlier, which you still hear being invoked today as if it’s the most obvious thing in the world: “eat less, exercise more.” Simple arithmetic. To his credit, Taubes does a masterful job of debunking this dangerous oversimplification.
Taubes goes on to argue, correctly, that creating long-term health by controlling calorie consumption does not work—a very important observation little understood by professionals and nonprofessionals alike. Most people cannot maintain significantly lower calorie consumption for long periods of time, even though they may be able to do so for a short while. That is, “diets” don’t work—not because our willpower isn’t up to it but because of our biological inability to healthfully maintain the substantially lower calorie consumption required to significantly decrease disease formation.8 In any case, Taubes says, generally it is not the amount of calories consumed that matters most but the way calories are metabolized and distributed throughout the body (something we’ll discuss in more depth in a few pages). In fact, Taubes argues that increased calorie consumption is the effect, not the cause of obesity—that we gain weight for other reasons and then require more calories to sustain that weight. Something else is causing obesity, and it is doing so by determining how our ingested calories are metabolized and used.
I applaud Taubes’ demolishing the calorie hypothesis. In fact, I have long said that we should be careful not to emphasize the “calories in; calories out” hypothesis or describe calories in precise quantities as if they are physical entities, like molecules, that have structure and form, because doing so only gives them added importance.
A calorie is only a measure of energy contained within a molecule, especially within the chemical bonds that bind atoms. Think of a pile of wood. We know that there is energy in that pile of wood, but we cannot see or feel it. When we put a match to the wood, however, we feel that energy escaping as the wood bursts into flames. The calorie contents of nutrients are also determined by measuring the heat nutrients release when burned. To calculate this, macronutrients (fat, protein, and carbohydrates, the nutrients that provide the vast majority of the weight of food) are burned in controlled conditions in a laboratory, and the heat emitted—the temperature change—is measured as calories. (I prefer to call this property “energy” but will stick with “calories” here because of the term’s broad familiarity.)
The amount of calories needed to produce a noticeable change in body weight, up or down, is very small—a notion that also sidetracks our emphasis on calories. A difference of fifty calories can be difficult to distinguish in the context of a day’s total food intake; it’s equivalent to an average of less than a teaspoon of oil per day. Yet a difference of fifty calories retained by the body per day can theoretically cause a gain or loss of five to ten pounds of body weight per year.9 The problem is that consumption of calories does not equal retention of calories; retention of calories is not something we can consciously control by counting. So, in this respect, Taubes is correct: calorie intake or expenditure, except in the extreme, does not matter as our findings in China confirm.10
WHERE TAUBES GETS IT WRONG
Taubes parts company with the evidence when he gets into the identification of where “bad calories” come from. Taubes sees excess consumption of calorie-contributing carbohydrates (the second of the three competing theories mentioned previously) as the root of all dietary evil. In his view, the consumption of sugar (table sugar or sucrose) and other carbohydrates (i.e., refined carbohydrates, such as starch and fructose) is responsible for the obesity epidemic in the United States and much of the rest of the world. And he blames this spike in carbohydrate consumption on the government’s promotion of the third competing theory: that calories from fat make us fat. In Taubes’ view, the fear of fat engendered by government low-fat policies drove the American public straight into the arms of a high-carb diet because it encouraged the replacement of this fat with carbohydrates. In short, Taubes says that too many carbs is the problem, while the government (or his interpretation of it) says the problem is too much fat.
Taubes argues on historical and scientific grounds that excess fat consumption cannot account for the alarming rise in obesity during the past thirty years the way government pronouncements suggest. Most readers will be familiar with the widespread recommendation to use low-fat foods, as well as the multitudes of “low-fat” food products on the market. Taubes presents a seemingly plausible account of how scientists working in this field got it wrong, partly because they were not very imaginative and partly because they became entrenched in a worldview that discouraged professional challenge against the much-publicized low-fat-focused hypothesis lest they be ridiculed or even risk losing their professional standing. Fat, not carbohydrates, Taubes says, should be our primary source of energy. Fat is good, he says, and not something merely dumped into a body reservoir that eventually becomes adipose tissue.
Before going further, let’s consider what a carbohydrate actually is, especially because Taubes rather arrogantly lambasts scientists for not knowing the properties of this nutrient. (In my experience, it’s really journalists like Taubes, corporate marketing agents, and even some clinicians who are confused about carbohydrates’ definition and meaning.)
The Diversity of Carbohydrates
Carbohydrate is a nutrient found almost exclusively in plants. It is a collection of simple to very complex chemical molecules. Simple carbohydrates include monosaccharides (like glucose, fructose, galactose, mannose, etc.) and disaccharides, which are made up of two chemically bonded monosaccharides (like sucrose [table sugar, made from glucose and fructose] and lactose [milk sugar, made from glucose and galactose]). Linked chains, or polymers, of three or more monosaccharides are called polysaccharides. Glucose (the same molecule as in blood sugar) is the most common monosaccharide unit in polysaccharide chains, with fructose being nearly as common in some foods. Starch, which is the primary polysaccharide in foods like potatoes and cereal grains, is a network of long chains of glucose molecules.
Monosaccharides and disaccharides are often considered “simple” carbohydrates because their molecular size is small, they readily dissolve in water, and they are easily digested and absorbed into the bloodstream. Some people infer that starches are also “simple” because they, too, dissolve in water (though they turn it into a gel or paste) and are readily broken down during digestion into glucose, which is then absorbed into the bloodstream.
Other carbohydrate types are much more complex. Elaborate networks of polymers are formed from chains of monosaccharides, sometimes also including amino acid and fat-like molecular side chains. These polymer networks exhibit a wide variety of chemical, physical, and nutritional properties. A large group of substances generally referred to as the dietary fiber group, for example, are, unlike their simple carbohydrate cousins, generally not digested and absorbed in the gut. Nonetheless, these complex, fiber-like substances still participate in vitally important biological activities: they interact with intestinal microorganisms that break them down into products that benefit the rest of the body, especially the intestines. Indeed, simple and complex carbohydrates, when working together, provide diverse health benefits, including the provision of energy.
Whenever we encounter diversity in nature, we should be slow to dismiss it as unnecessary or unfortunate. A broad spectrum of carbohydrate digestibility and function is very important: it allows the body to adapt to different conditions, ranging from the need for a quick burst of energy to the facilitation of digestion and absorption of other nutrients in the gut.
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