Is a calorie just a calorie? Whether from a wheat bagel or a Snickers bar, is 300 calories, regardless of the source, just that: 300 calories? The experts say yes. This thought process then leads to the positive-caloric-balance hypothesis as an explanation of weight gain and obesity. In short, eat more calories than your body uses and you will gain weight. Seems logical.
These same researchers will quickly point to the first law of thermodynamics (the law of energy conservation) to bolster a cause and effect that implies that any change in body weight must equal the difference in the amount consumed versus the amount expended. This energy balance equation looks like this:
Change in energy stores = Energy intake – Energy expenditure
To this day, nearly a century of obesity research has been based on this simple formula. However, most obesity researchers and public health officials rely only on the right side of the equation (Energy intake – Energy expenditure) to explain obesity, conveniently ignoring the left side (Changing in energy stores). These experts correctly assume that a positive caloric balance is associated with weight gain, but they assume without justification that positive caloric balance is the cause of obesity. Any adult female can attest to the role of hormones in weight gain—a gain that is unrelated to caloric balance. This is made more clear during pregnancy, when hormone-driven evolutionary forces promote hunger, weight gain, and lethargy—all to assure that sufficient calories are available for the newborn. This and other misconceptions of weight gain and obesity have lead to over a century of misguided obesity research that continues to this day.
In a series of blog posts beginning with this one, we will lay out some basic evolutionary, biological, and cultural adaptations (and maladaptations) that may provide some insight into weight gain and overall health and well being.
To cook or not to cook (if so, how long?)
With all due respect to the raw food movement, cooked food just tastes better. And from an evolutionary perspective, the application of heat to our food has played a significant role in the success of our species. But are we cooking our food a little too much and for too long?
Cooking makes a food more digestible than the same food without the benefit of cooking. In carbohydrate-rich foods, the application of heat to a moisture-rich food (e.g., a potato) causes hydrogen bonds in the glucose polymers to weaken, causing the tight crystalline structure to loosen and gelatinize. As long as water is present in the food or the cooking environment, the starch will gelatinize. Once consumed, the gelatinized starches are more easily cleaved by our digestive enzymes, thus more digestible. The same process occurs in meats through denaturation of proteins through the application of heat.
From an evolutionary perspective, we may be cooking some of our food a tad too much for cultural and culinary reasons, and in the process affecting some time-honored physiological requirements of the human body—specifically, the role of the stomach in energy balance, satisfaction, and hunger.
It was not that long ago that all of our foods were minimally processed. In short, more crunchy, more grainy, and definitely less refined. There is no doubt that our ancestors would marvel at the sleek and gelatinized angel hair pasta of today and the pasty softness of a steamed carrot torpedo. While convenient and tasty, our modern processing (in the case of the finely milled flour in the pasta) and cooking techniques (“hyper” steamed veggies) have moved digestion from the stomach to the stovetop. All the extra cooking in our modern lifestyle has slowly eliminated—or at least reduced—the role the human stomach evolved to play in digestion. And herein lies the discordance between our modern lifestyle and its nifty technological tools and cultural preferences, with our evolution-determined physiology and specifically, energy balance.
The carrot-like tuber your ancestors ate either raw or minimally cooked has been replaced by foods with a texture like baby food. This texture comes from weakened glucose polymers caused by the application of super-efficient cooking techniques. The modern cooked carrot is easily digested and therefore rapidly moved through the stomach. It’s safe to say that modern humans are experiencing some of the fastest rates of gastric emptying in human history. Gone are the days when minimally processed foods stayed in the stomach for two, three, or even four hours. There’s no longer a need for food to stay in the stomach; the stovetop started the digestion well ahead of ingestion, greatly speeding the work of gastric enzymes.
This effect is nicely captured in the widely popular Glycemic Index (GI). The GI ranks foods according to their effect on blood glucose levels. High GI foods, like highly processed donuts and sugary soft drinks, cause a rapid rise in blood glucose and subsequent insulin levels. Not good. Foods that are processed less generally have a lower GI.
But cooking has a significant and often unappreciated effect on the GI of a food. A raw carrot, which takes some crunching to break down, is transferred to the stomach, where some time-honored digestion takes place in a natural and slow way. Thus, a raw carrot has a low GI (about 16). However, a peeled and boiled carrot is easy to chew and rapidly processed in the stomach, as it has been predigested on the stovetop. This cooked carrot has a higher GI, around 60. This translates to rapid gastric emptying and subsequent rapid absorption—resulting in elevated glucose and insulin levels. Not good.
So what does this have to do with weight gain? Aside from some issues related to elevated levels of insulin in the blood—which has a dramatic impact on fat metabolism (something we will cover in a subsequent post)—the processed carrot versus the unprocessed carrot is tinkering with some evolutionary processes related to thermogenesis, and may be playing an unrealized role in our national epidemic of obesity. This is nicely demonstrated in an elegant study recently published by Japanese researchers. (Hang in there, almost to the point!)
In this study, a team of Japanese scientists divided 20 rats into two groups of 10 at four weeks of age. Over the next 22 weeks, both groups ate a nutritionally identical diet of rat chow. However, for one group of rats, the hard-to-chew pellets were injected with a tiny bit of air, making them softer and easier to chew. This is more or less similar to our raw versus steamed carrot discussion above.
The air-injected pellets were more like breakfast cereal and required about half as much force to chew and break down. The hard and the soft pellets were the same in how they were cooked, in their nutrient composition, and in their water content. Based on the “calorie is a calorie” argument and the first law of thermodynamics discussed above, rats reared under identical conditions and consuming the same nutrition should grow at the same rate and size and with the same amount of body fat and overall weight. But they did not.
Even though the rats had identical energy intake throughout the 22-week experiment, the rats which consumed the soft pellets slowly become heavier. It was gradual at first, but the rats fed soft pellets weighed about 6% more than the harder pellet eaters and had 30 percent more abdominal fat—enough to be classified as obese. The difference documented was due to the cost of digestion.
Before and after feeding, the researchers measured the body temperature of each rat. At every meal the rats experienced a rise in body temperature, but the rise was less in the soft pellet group. The difference in temperature was most significant between the groups within an hour of ingesting a meal, when the stomach is churning and secreting. The researchers concluded that the softer diet resulted in obesity simply because it was less costly to digest. Increased heat during digestion burns calories at a faster rate, similar to the weight loss we experience when we’re sick with a fever.
We all know that weight gain does not happen over night. It’s a slow process that takes place over long periods of time and can fluctuate dramatically. And because this is a slow and gradual process, we also know the body is constantly trying to regulate energy intake to energy expended. The body strives for balance, not an imbalance. This is why you are hungry after vigorous physical exercise; your body wants to replace the calories you just burned. This also explains why a lumberjack needs 5,000 to 8,000 calories a day, but an advertising executive might only need 2,500 or so. If exercise were the answer, then all meter maids would be thin. But they are not.
Weight gain among a given population has more to do with tinkering with evolutionary processes than with sloth or one’s willpower. It’s uniquely biological. If the experts are correct in that small changes, like 90 minutes of exercise a week or 100 calorie snacks are the answer, then paying attention to the level of processing of our food discussed in this blog should have at least as much merit in fighting the obesity epidemic.
We are not advocating a raw food diet—oh hell no! That’s a sure way to guarantee you don’t get sufficient nutrients and will surely bore yourself and your loved ones to near death—literally. And raw beef is downright dangerous. We are suggesting that you take a closer look at the amount of processed food you eat. Think, before you steam rice for 15 minutes, that maybe 12 minutes would be enough— making it a little crunchier and therefore a tad harder for your stomach to break down. This will, in turn, elevate your body temperature slightly as your stomach churns and burns calories. You might also consider doing the same with steamed broccoli. In addition, don’t cut off and throw away the stalks and eat just the yummy crown. Cut that fiber-rich stalk into thin slices and steam away. By increasing the fiber in your meals, you will also give your stomach a chance to do its job as well.
The multi-grain crust at NAKEDpizza is a great starting point, far better than the over-processed offerings at other pizza places as well. Live long. EatNAKED, friendos.