Over the years I have read about, been lectured to about, and even tried a number of the fad diets that have been popularized in the media. Most of these feeding regimes have their foundations in the very casual (and often very selective) reading and interpretation of nutritional science literature. Fragments of ideas and stretches of inference from very slim data sources regularly get translated into diet books or TV celebrity-endorsed diet programs that have little or no long-lasting benefit and even less basis in physiological reality.
In Wikipedia (my quick source for background information on almost everything) thirty-four fad diets are listed. Many of these diets focus on abundant consumption of a single type of food (the grapefruit diet, the morning banana diet, fruitinarianism, etc.). While others stress avoidance of entire food groups (like carbohydrates (Atkins diet, the Zone diet, the Sugar Busters diet)) or the massive consumption of those same groups (like carbohydrates (Good Carbohydrate Revolution, the Pritkin Principle)). Further, many of these fads diets define themselves by connection to very visible, highly fit groups or individuals (the Israeli Army diet, the Scarsdale Medical diet, the South Beach diet) without full consideration of the pre-selection and non-dietary forces that might be operational in generating each of these remarkably fit groups of people. The connecting principle of these diets, though, is that they are not scientific and also that are not, in the long run, effective.
One very recent fad diet that has tried to wrap itself in a cloak of science is the Paleolithic Diet (also called the Paleo Diet or the Caveman Diet). The foundation of this diet is evolutionary: Humans evolved in extremely stressful environments for several million years. It is logical, in this evolutionary framework, to assume that Natural Selection not only molded our limbs and jaws and brains but also selected for optimal digestive and metabolic systems based on the available foods in our ancestral ecosystems. Therefore, the Paleo Diet maintains, if we only eat those foods for which our bodies are adapted, we will be healthy and fit and happy!
Let’s poke at these ideas a bit and see if they hold up to any scrutiny:
- We must remember that Paleolithic humans lived short, and probably quite brutish lives (although this idea is disputed by some of the paleo-promoters). The logic of a very high rate of infant mortality, a high risk of serious injury particularly in the active-hunter age groups (ten to thirty years old), and little or no potential for effective medical intervention for the other disease or injury events that plague everyone through life makes the conventional estimate of life spans between twenty-five and thirty years quite reasonable. Was there time in these short life spans for the more subtle impacts of diet to be selected for? Can’t twenty-year-old’s eat anything and thrive? (I think that I lived on tortilla chips and salsa when I was twenty!).
- We can only guess what foods our paleolithic ancestors ate and in what proportions they actually ate them. Further, early human populations living in different ecosystems, quite logically, ate very different foods. Even if we assume that there was a sufficient selective force asserted by diet, the direction of that force would be different in different human cohorts.
- One should not ignore the idea that the diet selection force for humans was for an omnivory of almost unprecedented flexibility! Humans had no control over their food sources and had to eat and be able to digest and metabolize almost every type of food stuff in their environments.
- And, finally, there is a prevailing myth that humans moving into the ages of agricultural and technological existence stopped evolving: Culture took over from Nature. This simply is not true. Humans evolved under the selective influence of agriculture (to better digest the foods being produced in our agroecosystems) and have continued to evolve to living in densely populated urban areas, to living in extreme environments, and to living with our ever changing, surrounding microbial world. Even if the true diet of our paleolithic ancestors could be described, we are not that person anymore!
One of the reasons that these fad diets have been so popular (and abundant!) is that we in our industrialized society are getting fatter and sicker with each passing year. “Metabolic Syndrome” is the name given to the collective package of this set of modern maladies. Metabolic Syndrome involves some combination of three or more of the following conditions: central obesity (fat accumulation around the trunk of the body and waist in a person who is overweight), high blood pressure, low levels of the “good” cholesterol (HDL’s), elevated levels of triglycerides, and elevated fasting glucose levels. Also, often included in this list of metabolic syndrome signs is insulin resistance (or “pre-diabetes”).
In the United States 34% of adults have Metabolic Syndrome. Worldwide, 25% of adults have either a partial or complete set of Metabolic Syndrome signs.
What causes Metabolic Syndrome? It is at its core a consequence of an imbalance between energy consumption and energy use by the body. Quite simply, too many calories are being consumed and too few calories are being used in metabolism. This simple equation, though, has had many very subtle, but very important tweaks. Possibly, it is not just the amounts of calories being consumed but the types of calories (this is the foundation of many of the fad diets I listed above!). Possibly, modern foods because of their specific plant sources or because of the nature of their cultivation, growth, processing or preparation tip the metabolic balance of a person’s physiology to obesity and the array of Metabolic Syndrome signs. Possibly, our modern life style has so modified (or destroyed) our bacterial microbiome that these important mutualistic organisms no longer help us to control the flow of energy through our metabolisms. Any of these things are possible, but the exact cause of Metabolic Syndrome is not yet known.
The factors that are correlated with Metabolic Syndrome are very straightforward: diet (especially the consumption of sugar-sweetened beverages), sedentary behavior (low levels of physical activity and exercise), disrupted sleep patterns, stress, excessive alcohol consumption, and aging. There may also be some genetic predispositions to developing Metabolic Syndrome.
Next week, I will talk about another way to look at Metabolic Syndrome, a way that focuses on our day/night patterns, our circadian rhythms of mental, behavioral and physiological activity rather than on the actual food we consume. Fasting is a logical way to modify the health effects of this model and recent studies on the impact of food deprivation have revealed some very interesting insights into our physiology.
Until next week!