In the last two blogs on obesity, I made the following points:

  1. The entire world is becoming more obese, and the United States is leading the pack.
  2. The most common measure of obesity is “body mass index” (BMI).
  3. There are many negative health outcomes associated with obesity.
  4. Some studies report that obesity can confer health benefits (the “obesity paradox”), but these results don’t hold up when measures of fatness other than BMI are used.
  5. Recent data indicates that about 40% of obese people are actually “fit” and metabolically normal, and do not have increased morbidity, cancer, or cardiovascular disease.
  6. The primary cause of obesity is probably the consumption of excess calories and/or carbohydrates, most likely sugar.
  7. The research concerning the relationship between energy expenditure and obesity is not conclusive—although there is a correlation in the United States between decreased activity and increased obesity, studies indicate that there is no difference in energy expenditure between developed and developing countries.    

This last point, which is pretty counterintuitive, supports the view that increased obesity is mainly due to the consumption of excess calories.  In fact, a 2009 study found that excess calories ALONE can account for the U.S. obesity epidemic.  When researchers looked at dietary changes since the 1970’s, they found that children are consuming an extra 350 calories per day and adults are consuming an extra 500—equivalent to one can of soda for a child and one hamburger for an adult.

So if we assume that obesity in the United States (if not the world) is generally due to over-eating and/or -drinking, the logical question is whether there is one particular food or drink that is the culprit.  

Since sugar is found large quantities in both food and drink, that seems to be a good place to start.  It turns out that the U.S. has had a long-standing love affair with sugar, and our attachment to it has only grown stronger over time.  As you can see from the following graph, in the early 1800’s the average person consumed 4 pounds of sugar per year; by 1850 it was 50 pounds, and by 2000 it was almost 120 pounds.

[The data in the graph above is drawn from U.S. Dept. of Commerce and USDA reports concerning sugar production because data concerning consumption wasn’t available.  In order to account for waste, the author of the graph (a researcher at the University of Washington) reduced all the production data by approximately 30% to arrive at estimated sugar consumption.]

This striking graph shows that in the United States, we consume something in the neighborhood of 100 pounds of sugar per person per year.  In this case, the word “sugar” means sweeteners such as high-fructose corn syrup, sugar, and maple syrup, but not naturally-occurring sugars in fruit and vegetables (and probably not lactose, the sugar in milk, but that is just a guess on my part).  

And what do these levels of sugar consumption mean in terms of calories?  It appears from the graph that in the early 1970’s, we were consuming about 80 pounds of “sugar” (sweetener) per year, which is .22 pounds/day or 330 calories/day (assuming that one pound of an “average” sweetener has about 1500 calories).   Today we consume about 100 pounds of sugar/year or 0.27 pounds/day, which is 405 calories.  That’s an increase of 75 calories per day from 1970 to 2010, which doesn’t sound like much, but when you do the math, it turns out to be a whopping 27,375 calories per year.

By using the old rule of thumb commonly found in diet books that says “3,500 calories equals a pound of fat,” you would conclude that if you consume 75 extra calories every day, you will gain 7.8 pounds of fat in a single year—and if you maintain this practice for 20 years, you will be carrying around an extra 156 pounds of fat!  

(Okay, I don’t believe that and neither do you—and indeed, recent research results are rejecting this old “rule.”  But rather than getting into those studies, suffice it to say that an increase of a mere 75 calories per day would probably NOT result in an obesity epidemic.  Yes, those extra calories could result in a weight gain of 6 or 7 pounds over the course of ONE year, but according to more recent models, it would level off after that because extra fat requires additional energy to maintain itself.)

Okay, so far we have only accounted for an additional 75 calories/day.  If we assume that the “average” American (both adults and children) consumes about 425 excess calories each day, we still need to find another 350 calories.  Let’s look at soft drinks and fruit drinks, which constitute a prime source of sugar in this country.  In fact, the National Health and Nutrition Examination Survey by the Centers for Disease Control and Prevention estimates that more than 40% of our sugar intake is in the form of this “liquid candy.”

According to the above graph, it is estimated that in 2005, each person in the United States drank about 50 gallons of soft drinks (sodas):  about half a liter a day.  At about 1,520 calories per gallon, that is 76,000 calories/year or 208 calories/day.  (I can’t explain the discrepancy between the result that we get from the sugar-consumption graph (75 calories/day) and the result from this soda-consumption graph (208 calories/day), unless the sugar estimates in the first graph are way off.   But either way it is clear that the sugar in sodas is probably a major contributor to our excess calorie intake.)

At this point in the story, let’s look more closely at the different KINDS of sugar in the American diet and how that has changed over time.

Sugar, as you may know, is not just one kind of molecule.  There are many, many different types of sugars, but for the purposes of this discussion, I want to focus on just three of them:  sucrose, glucose, and fructose.  

Everyone has heard of sucrose, I’m sure.   Composed of two simpler sugars (glucose and fructose), sucrose is the white granulated stuff you put in your coffee, also called “table sugar.”   It’s dang tasty and it’s everywhere, in spite of being reviled as nothing but empty calories.  And contrary to what a lot of people think, sucrose is completely “natural, “ since it is the sugar found in sugar cane and sugar beets.  It also constitutes 90% of maple sugar and makes up a large portion of floral nectar, which is ingested by bees and then vomited up (along with an enzyme called invertase that breaks the sucrose down into its simpler sugars) to make honey, which itself is about 50% glucose and 50% fructose.

Glucose, also known as “blood sugar,” is the kind of sugar that is first produced by plants from sunlight, and thus can be thought of as the “foundational” energy source upon which all life depends.  Since starches are just chains of glucose molecules linked together, what you get when they are broken down by digestion is glucose, which is readily absorbed by the blood stream and provides fuel for brain and body.  

And finally there is fructose, which is also known as “fruit sugar” because it is found in high concentrations in figs, grapes, pears, and many other fruits.  The majority of people, however, probably know it as “high fructose corn syrup” (HFCS), which has become the primary sweetener in soft drinks during the last 40 years,.  

This next graph tracks sweetener consumption over time just like the first graph did, but this time fructose and obesity are plotted as well.  As you can see, there is a correlation between obesity and the consumption of fructose, as both of them began to rise at about the same time.  But even though consumption of fructose, and all sweeteners, began to decline about 15 years ago, the incidence of obesity did not.

The last graph (below) tells an interesting story about the consumption of high-fructose corn syrup during the 40-year period from 1970 to 2010.  The process for making HFCS was developed in the 1950’s and fine-tuned during the next couple of decades, but for all intents and purposes, it was largely absent from the American diet until the 1970’s.  Consumption grew rapidly thereafter, particularly in the mid-1980’s when falling corn prices made it the sweetener of choice for soft drinks, and its use continued to increase until the late 1990’s.  But amid concerns about HFCS’s role in the obesity epidemic and its other potential negative effects on human health, consumption has been declining since the turn of the century—even though recent studies indicate that the fault may lie with excess sugar consumption in general rather than HFCS in particular.

When I started searching for those 425 extra calories that appear to be causing the obesity epidemic, I fully expected to find them in a soft drink bottle.  But while soda  is clearly one of the culprits, at this point it doesn’t seem to be the only one.  I’m beginning to think that the answer may be more straightforward:  we are simply consuming too much.  Of everything.

We could stop with our “sugar” story right there, but I can’t help thinking that there is more to be said about fructose and health, as well as carbohydrates in general.  Also, I can’t get rid of the niggling thoughts in the back of my mind about those studies that found no association between energy expenditure and obesity.  

And with that, I think I’m going to go have a Mountain Dew.