What makes you fat: too many calories, or the wrong carbohydrates?

Why do so many of us get so fat? the answer appears obvious. “The fundamental cause of obesity and overweight,” the World Health Organization says, “is an energy imbalance between calories consumed and calories expended.” Put simply, we either eat too much or are too sedentary, or both. By this logic, any excess of calories—whether from protein, carbohydrate or fat (the three main components, or “macronutrients,” in food)—will inevitably pack on the pounds. So the solution is also obvious: eat less, exercise more.
The reason to question this conventional thinking is equally self-evident. The eat less/move more prescription has been widely disseminated for 40 years, and yet the prevalence of obesity, or the accumulation of unhealthy amounts of body fat, has climbed to unprecedented levels. Today more than a third of Americans are considered obese—more than twice the proportion of 40 years ago. Worldwide, more than half a billion people are now obese. Besides getting fatter, we are also developing more metabolic disorders, such as type 2 diabetes, which is marked by hormonal abnormalities in the processing and storage of nutrients and is far more common in obese individuals than in lean ones.

The dissonance of an ever worsening problem despite a seemingly well-accepted solution suggests two possibilities. One, our understanding of why people get fat is correct, but those who are obese—for genetic, environmental or behavioral reasons—are unable or unwilling to heal themselves. Two, our understanding is wrong and hence so is the ubiquitous advice about how to make things better.
If the second option is true, then maybe what makes us fat is not an energy imbalance but something more akin to a hormonal defect, an idea embraced by European researchers prior to World War II. If so, the prime suspect or environmental trigger of this defect would be the quantity and quality of the carbohydrates we consume. Under this scenario, one fundamental error we have made in our thinking about obesity is to assume that the energy content of foods—whether avocado, steak, bread or soda—is what makes them fattening, not the effects that these foods, carbohydrates in particular, have on the hormones that regulate fat accumulation.

The research
To test this last hypothesis a new research program has been planned by Gary Taubes and The Nutrition Science Institute and described in the Scientific American special food issue. This study will entail having subjects consume 80% of their calories as fat, and 5% as carbohydrates, in an effort to determine if consuming calories as fat results in better insulin control and in weight loss.

The Hormone hypothesis

To understand what makes the hormone hypothesis of obesity so intriguing, it helps to grasp where the energy-balance hypothesis falls short. The idea that obesity is caused by consuming more calories than we expend supposedly stems from the first law of thermodynamics, which merely states that energy can neither be created nor destroyed. As applied to biology, it means that energy consumed by an organism has to be either converted to a useful form (metabolized), excreted or stored. Thus, if we take in more calories than we expend or excrete, the excess has to be stored, which means that we get fatter and heavier. So far, so obvious. But this law tells us nothing about why we take in more calories than we expend, nor does it tell us why the excess gets stored as fat. And it is these “why” questions that need to be answered.

Specifically, why do fat cells accumulate fat molecules to excess? This is a biological question, not a physics one. Why are those fat molecules not metabolized instead to generate energy or heat? And why do fat cells take up excessive fat in some areas of the body but not others? Saying that they do so because excess calories are consumed is not a meaningful answer.

Answering these questions leads to consideration of the role that hormones—insulin, in particular—play in stimulating fat accumulation in different cells. Insulin is secreted in response to a type of carbohydrate called glucose. When the amount of glucose rises in the blood—as happens after eating a carbohydrate-rich meal—the pancreas secretes more insulin, which works to keep the blood glucose level from getting dangerously high. Insulin tells muscle, organ and even fat cells to take up the glucose and use it for fuel. It also tells fat cells to store fat—including fat from the meal—for later use. As long as insulin levels remain high, fat cells retain fat, and the other cells preferentially burn glucose (and not fat) for energy. The main dietary sources of glucose are starches, grains and sugars. (In the absence of carbohydrates, the liver will synthesize glucose from protein.) The more easily digestible the carbohydrates, the greater and quicker the rise in blood glucose. (Fiber and fat in foods slow the process.) Thus, a diet rich in refined grains and starches will prompt greater insulin secretion than a diet that is not. Sugars—such as sucrose and high-fructose corn syrup—may play a key role because they also contain significant amounts of a carbohydrate called fructose, which is metabolized mostly by liver cells.

The author's conclusion

The result, according to the hormone hypothesis, is an ever greater proportion of the day that insulin in the blood is elevated, causing fat to accumulate in fat cells rather than being used to fuel the body. As little as 10 or 20 calories stored as excess fat each day can lead over decades to obesity.

The hormone hypothesis suggests that the only way to prevent this downward spiral from happening, and to reverse it when it does, is to avoid the sugars and carbohydrates that work to raise insulin levels. Then the body will naturally tap its store of fat to burn for fuel. The switch from carbohydrate burning to fat burning, so the logic goes, might occur even if the total number of calories consumed remains unchanged. Cells burn the fat because hormones are effectively telling them to do so; the body's energy expenditure increases as a result. To lose excess body fat, according to this view, carbohydrates must be restricted and replaced, ideally with fat, which does not stimulate insulin secretion.  This alternative hypothesis of obesity implies that the ongoing worldwide epidemics of obesity and type 2 diabetes (which stems to great extent from insulin resistance) are largely driven by the grains and sugars in our diets. It also implies that the first step in solving these crises is to avoid sugars and limit consumption of starchy vegetables and grains, not worrying about how much we are eating and exercising.

A different point of view

The right nutrition question is “What should we eat to have the longest, healthiest life?” Instead, author Gary Taubes is asking “What should we eat to lose weight?” There are many ways to lose weight, and still be sick and die. Taubes’s study isn’t even designed to measure health or longevity. So when his study shows that one can lose weight with an low-carb diet, he will argue that obese people should go on a low-carb diet because obesity is correlated with many fatal diseases. However, a low-carb diet changes that correlation. There are plenty of thin people who die of heart disease.

According to John Tanner, -Ph.D. Director, NuSci, The Nutrition Science Foundation- Gary Tauber's study will most likely result in a confusing and misleading result because it is asking the wrong question. Instead, the right premises will lead to a clear answer. In his intense study of research results Tanner says he found a consistent pattern emerging: a whole-food plant-based diet low in fat and high in carbs results in the total elimination of heart disease and dramatic reduction and/or reversal of type 2 diabetes, stroke, high blood pressure, cancer, and about 30 other diseases. And as a nice side effect, obese and overweight people lose weight, often in a dramatic fashion.

What's your priority? What is worth the price of a diet: your look or your health? Re-thinking your goals will help you stay committed to a healthy diet...


Sources: http://www.scientificamerican.com/, http://www.nusci.org/