At a time when the obesity epidemic is overwhelming healthcare systems globally, when it seems that almost everyone is “watching their weight,” when first-years are worried about “the freshman 15,” and when you just want to keep your summer body, it might surprise you that everything you have ever known about counting calories is wrong. Even if you are the Soup-Nazi of calorie counting, the important factor may not be how many calories you eat, but what type of calories and how they are cooked.
Food is the energy supply for our bodies. Enzymes in our digestive tract break down the energy carried within food in the form of carbohydrates, fats and proteins. We calculate the energy trapped within all foods with a unit known as kilocalories or more colloquially as calories – the amount of energy required to heat one kilogram of water by one degree Celsius. Carbohydrates and proteins provide about four calories per gram, while fats provide approximately nine calories per gram.
Calorie counts on packaging labels are based on these numbers. However, these approximations are based on laboratory experiments, which are then extrapolated to estimate the amount of calories that people with physiological differences derive from different foods. New research in human biology and nutritional science reveal that this assumption is far too simplistic. There are a number of factors that influence exactly how much energy someone gets out of a given food, including how the food is prepared (which changes the food’s structure or chemistry), how much energy the body expends to break down different foods, and whether the food has evolved mechanisms to survive human digestion.
While the values of how many calories each molecule provides may be accurate, it (and therefore food labels) does not take into account the digestibility of each food source or how much energy our body requires just to break them down. The U.S. Department of Agriculture found that when people eat almonds, they receive, on average, just 129 calories per serving rather than the 170 calories reported on the label. In general, proteins may require as much as five times more energy to digest as fats do. On the other side of the spectrum, sugary carbohydrate-based foods like honey barely employ the digestive system: they are broken down in the stomach and easily move across the walls of the small intestine into the bloodstream.
Modern calorie labels also fail to account for the effects various cooking techniques have on how much energy we get from food. Every human culture in the world has technology for modifying its food. Some scientists propose that getting the added energy on less time and effort allowed humans to develop and nourish exceptionally large brains-relative-to-body size.
Rachel Carmody, a former PhD student at Harvard University, tested the effects of food preparation on energy consumption. She fed genetically similar mice sweet potatoes or lean beef, either cooked or raw. The mice were allowed to eat as much as they wanted for four days. The mice that were fed raw sweet potatoes lost around four grams of weight, but those on cooked potatoes actually gained weight. Similarly, mice eating cooked beef gained 1 gram more than those fed raw meat. This is apparently result of the fact that the heat hastens the unraveling of proteins, thus increasing their digestibility.
Even if two people eat the same diet, they would not extract the same number of calories out of it. People have a variety of intestinal lengths, enzyme productions, and microbial make-ups in their digestive tracts – which all leads to different calorie intakes. For instance, the bacterial community lining your intestines plays a much larger role than one might think. In humans, two phyla of bacteria dominate the gut: Bacteroidetes and Firmicutes. Research has shown that obese individuals tend to have more Firmicutes in their intestines. Researchers have proposed that some people are obese partly because the extra bacteria make them more efficient at metabolizing food. Instead of those calories being lost as waste, more nutrients make their way into the bloodstream – and, if not used, get stored as fat.
We could fix the current food labeling system to account for the special digestive challenges of each food and how each item is processed. But even if we entirely revamped the calorie counts, they could never be accurate on an individual level. The number of calories we extract depends on an enormously complex interaction between food, the human body, and its microbial army.
Merely counting calories based on food labels is an overly simplistic approach to eating a healthy diet. Even after rigorous, personalized calorie counting and strenuous exercise, one may still gain weight. There are currently two competing hypotheses as to why we gain weight. The Energy Imbalance hypothesis is the “calorie-counting” hypothesis. It is the conventional explanation focusing on Excess Energy = Energy Consumed – Energy Expended. This excess in energy is then converted into fat and stored on the body. According to this model, the only way to lose weight would be to eat fewer calories or expend more calories, i.e. exercise more. However, there is another explanation that has accrued some supporting evidence. The Hormone Imbalance hypothesis focuses on the complex physiological regulation of fat cells. Consuming a carbohydrate-rich meal raises blood sugar levels, which activates the release of the hormone insulin. Fat cells then respond to high levels of insulin by holding on to their fat storage and adding to them. Weight gain occurs when insulin levels, and a number of other hormones, remain elevated for long periods of time. To lose excess body fat, carbohydrates must be restricted and replaced with an unregulated amount of calories from fat and protein, which do not stimulate insulin secretion.
For decades, weight gain has solely been explained through the “calorie-counting” hypothesis. However there are number of areas where this explanation falls short, for instance: What is the mechanism through which fat cells accumulate fat molecules? Why do fat cells take up excessive energy in some areas of the body but not in others?
While these polar explanations have both accumulated some significant evidence, they have never been rigorously tested against each other to see which one dominates or to what extent each affects weight gain. The Nutrition Science Initiative has recently begun funding research across the United States to investigate the matter, but the jury is still out.
The growing obesity problem is spreading around the world, but until we understand exactly how to fight back we cannot effectively and efficiently combat this issue. Modern research is finally revealing the science behind obesity and nutrition, but there is still much work to be done.