Money Talking
It doesn't require a stretch of the imagination to suggest that the sea of confusion flooding the media and bookshelves everywhere has at its source money, money, money! Back in 2012, nearly $20 billion were made in revenue for the weight-loss industry (1). People everywhere seem to be capitalizing on the money flow; and herein lies the crux of the confusion. Often times (but not always) bestselling authors and fitness gurus are more interested in helping themselves to your checkbook than in helping you. Don't get me wrong, there are some people out there who legitimately want to help, but there are way, way more people whose desires are not so benevolent.
The malevolent know that shiny new products sell. They know that consumers need to feel like they're being let in on a "secret"; and a powerful secret at that; one which no one in the mainstream yet knows of, and one which will make (insert desire here) become a reality.
Given the above, I think the real reason for all of the mass confusion about which foods, exercises, and lifestyle practices lead to health appears clear. People in the fitness industry are trying to outmaneuver--out secret--their competition. And many of these same people are making bank in the process.
Physiology Talking*
The reality of fat gain is multifaceted. Broadly speaking, however, a caloric surplus is ad rem a major culprit in the obesity epidemic. However, having an informed understanding of the underlying physiological mechanisms of fat accumulation can go a long way in upping the performance of your BS-detector.Hierarchy of Fuel Oxidation
Calories are not just calories but are rather composed of various macronutrients: fat, carbohydrate, protein, and alcohol. Each of these macronutrients is metabolized in a way unique from the others, especially as regards storage and relative thermic response (RTR).
- Alcohol
- Storage - There is no storage mechanism for alcohol. It is a toxin, and it must be immediately eliminated once ingested. It therefore takes first precedence above all other macronutrients regarding its disposal. The body will preferentially oxidize (burn as fuel) alcohol and thus suppress the oxidation of all other macronutrients (especially fat) as long as alcohol remains in the system.
- RTR - Highest of all macronutrients in order to ensure the alcohol is quickly and efficiently oxidized.
- Protein
- Storage - There is no formal storage mechanism for protein; though there is a circulating pool (reserve) of amino acids in the blood. Though there are physiological pathways by which protein can be converted into fat, the conversion efficiency is only 66%; whereas its efficiency in contributing to the synthesis of new muscle tissue is is 86%. Protein can also, via de novo gluconeogenesis, be converted into glucose. These metabolic conversions rarely occur under normal circumstances however.
- RTR - Very high due to the necessity of removing and excreting the nitrogen component of excess protein in order to preserve proper acid-base balance and prevent excessive ammonia concentrations.
- Carbohydrate
- Storage - Ingested carbohydrate is preferentially stored (up to 300-500g total) as glycogen in the muscles, liver, and to a small extent in the kidneys. Because carbohydrate storage is limited, and since blood glucose levels must be maintained within a narrow margin, carbohydrate is preferentially oxidized following ingestion; the result being the suppression of fat oxidation. Despite popular belief, carbohydrate is rarely converted into fat under normal circumstances. You would have to consume calories from carbohydrate in excess of your daily energy needs in order for de novo lipogenesis to occur. If someone's daily energy expenditure was 2,500 calories, said person would have to consume more than 625g of carbohydrate for an extended period of time before any noticeable fat gain would occur. The efficiency of its conversion into adipose tissue is 80%, and its glycogen storage efficiency is 90%.
- RTR - High to ensure that dietary carbohydrate is successfully oxidized in the event that there is no room for it in muscle, liver, or kidney tissue.
- Fat
- Storage - Fat can only be stored as fat. There are no physiological pathways for its conversion into anything other than fat. Though fatty acids can be stored in muscle tissue, fat is primarily stored as adipose tissue in virtually unlimited amounts. As a result, the need for fat's oxidation is minimized; hence this is why all other macronutrients will take oxidative precedence over fat in the context of a mixed meal. Dietary fat is converted into adipose tissue with an efficiency of 96%. It cannot be converted into non-adipose tissue.
- RTR - Low because there is little metabolic cost involved in fat storage.
Dietary Fat on Trial
Based on the above hierarchy of fuel oxidation, dietary fat looks pretty incriminated. Out of all the marcronutrients, it is the most likely to be stored as body fat in the context of a caloric surplus; and, admittedly, there are several other incriminating factors we have yet to discuss.
- High metabolic efficiency - As discussed above, the RTR of dietary fat is quite low. There is no strong physiological need to oxidize fat when other macronutrients are present. Thus, fat seems, by its very nature, designed for easy storage so that the body can more readily oxidize protein, carbohydrate, and alcohol.
- High energy density - 1g of dietary fat equals about 9 calories, whereas 1g of of carbohydrate equals about 4 calories, and 1g of protein equals about 4 calories (though protein may arguably equate to 3 when one considers its high thermic effect). Because it is so calorie dense, dietary fat is often indicted as being the primary agent of inadvertent over-consumption of calories.
- Low satiety - Dietary fat is notable for its negligible impact of satiation following consumption. Have you ever opened a new jar of peanut butter only to find it half empty quicker than Porky Pig could say "aequeosalinocalcalinoceraceoaluminosocupreovitriolic"? Though fat does effect satiety once it reaches the duodenum (the upper portion of the small intestine), this effect is often not fast enough so as to prevent rapid over-consumption.
Dietary Fat Acquitted
There are, however, a number of factors which demonstrate that dietary fat cannot hold full responsibility for the accumulation of fat.
- The Laws of Physics - Regardless of the macrocomposition of one's diet, an energy surplus is a surplus, a deficit is a deficit, and an equilibrium is an equilibrium. One cannot gain, lose, or maintain one's total body mass unless one's energy intake-expenditure ratio is such that it corresponds to a loss, maintenance, or gain of body mass. Though dietary fat is preferentially stored as body fat when other macronutrients are present, the question of whether or not it stays stored as body fat is a matter of energy balance.
- Health Benefits - A growing body evidence suggests that various types of fatty acids have protective properties. Monounsaturated fatty acids can lower total cholesterol, triacylglycerol, and LDL, while raising HDL. Polyunsaturated fatty acids (n-6 and n-3) are essential fatty acids which play an integral role in maintaining bodily health. They cannot be manufactured by the body and thus must be obtained from exogenous sources.
- Inconclusiveness of Research - Despite the efforts of many researchers, there is as of yet no conclusive evidence indicting dietary fat as the cause of obesity.
Psychology Talking
More than just mere reward value is a play here, however. There is a very real difference between the psychological response I have toward prime rib than the response I have toward Doritos. I like both, but I'm more likely to want to eat more Doritos after I've already eaten enough to satisfy my physical need for calories. This issue of liking vs wanting represents a very important yet subtle nuance in our understanding of the physiological and psychological factors which influence our desire to eat in reference to our need to eat. I like steak, but I rarely want to eat any after I've had a big meal. I like Pringles, and I always want to eat some, even after a big meal. What is it about these two foods which causes each to elicit different behavioral responses?
The complexities of food reward are, well, complex. While I must confess ignorance in regards to the finer points of the hypothesis, I do know that "junk food" is, in many respects, "engineered" to be more than just likable. Food scientists and researchers, who are quite aware of the behavioral impact which various combinations of tastes, textures, smells, and colors of foods have on humans, do a great deal of experimental work for major food corporations. They have the secret of how to make consumers constantly want their products down to a science.
Me Talking
If you asked me, I would say the main cause of obesity in America, and in Western societies, is a general decline in active lifestyles, a general increase in calorie consumption, a general increase in chronic stress, and a general decline in sleep duration and quality. I could add more factors to this list, but I think you get the picture. I think you can also understand now why the money driven fitness industry does little to disseminate the "truth" about how people really get fat. The causes are, more or less, no-brainers (yes, they are complex, but they aren't shocking). The solution, too, is a no-brainer. No-brainers, however, don't rake in the dough!
* Source: Aragon, Alan. Girth Control: The Science of Fat Loss and Muscle Gain.
* Source: Aragon, Alan. Girth Control: The Science of Fat Loss and Muscle Gain.
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