"Your body can't tell the difference"

"Your body can't tell the difference."  Most people in the U.S. have probably heard this phrase at least once.  It is a phrase from commercials funded by the Corn Refiners Association with reference to sucrose and high fructose corn syrup.  Sucrose is table sugar.  It is the most commonly used kind of sugar for baking and for sweetening hot beverages.  High fructose corn syrup is a form of corn syrup that has been altered to have around 55% fructose and 45% glucose.  It is most commonly used in soft drinks, but it is also commonly used in commercial baked goods and some types of sweet snacks.  The above phrase is a response to claims that high fructose corn syrup is extremely unhealthy.  The Corn Refiners Association claims that the human body "can't tell the difference" between high fructose corn syrup and table sugar.  Is this claim true?

The first thing we need to know is how the two sweeteners are similar and how they are different.  Table sugar is solid and dissolves to be fairly liquid in water.  Without considerable heating, a table sugar solution in water will not become thick or syrupy.  Corn syrup is thick and viscous and will not dry out into a solid form of sugar (in a dry enough environment with the right amount of heat it might be possible).  The physical differences make it clear that they are not identical.  Chemically though, they are very similar.  Both sucrose and high fructose corn syrup are composed of fructose and glucose.  Sucrose is 50% of each, and high fructose corn syrup is 55% fructose and 45% glucose.  So chemically there is little difference.  There is one other chemical difference.  Sucrose is exactly 50/50 because sucrose is composed of molecules that are fructose molecules bound to glucose molecules.  In high fructose corn syrup the glucose and fructose molecules are not bound together.  Clearly the two sweeteners are very similar.  The differences seem very minor.  If we want to figure this out, we are going to also have to look at how sugars are processed in the body.

The primary fuel for the body is glucose.  Cells can turn glucose into energy very easily.  Most other chemicals that the body can use for fuel (fats, proteins, and other sugars) must be converted to glucose before they can be used to produce energy.  When blood sugar is measured, the measurement is the amount of glucose in the blood.  The body regulates blood sugar by producing insulin, which tells cells to absorb glucose from the bloodstream.  If too much insulin is produced, cells will absorb a lot of glucose, reducing blood sugar to potentially unsafe levels.  If too little insulin is produced, cells will not be able to get enough energy and blood sugar will elevate to unsafe levels.  Insulin is produced in response to elevation in blood sugar, and the magnitude of the response is proportional to the magnitude of the increase in blood sugar.  An important factor in insulin response is how quickly sugars are converted into glucose and put into the bloodstream.  A small amount of sugar that gets into the bloodstream very quickly can cause an insulin response that will reduce blood sugar to unsafe levels.  If the blood sugar rises very quickly, the body expects that a lot of carbohydrates were consumed.  It responds by producing a lot of insulin.  If only a small amount of carbohydrates were consumed, they will quickly be absorbed, reducing blood sugar, but there will still be a lot of insulin telling cells to absorb more sugar.  This leads to low blood sugar.  Also, frequent high volume insulin production can stress the cells that produce insulin, eventually killing them.  This eventually leads to type 2 diabetes.  A metric has been developed to measure how various foods affect blood sugar.  This is called the glycemic index.  Foods with a high glycemic index cause rapid increases in blood sugar, while foods with a low glycemic index cause little or no increase in blood sugar.  A good diet will cause a small increase in blood sugar that lasts for a long time.  A diet that causes frequent or sustained large increases in blood sugar will ultimately lead to type 2 diabetes and potentially heart disease and other circulatory problems.  Now, how does this relate to sucrose and high fructose corn syrup?

The glycemic index of glucose is 100 (it is the reference).  The glycemic index of fructose is 19.  Fructose has the lowest glycemic index of all known sugars.  It would make sense that the higher ratio of fructose in high fructose corn syrup might give it a lower glycemic index than sucrose.  Unfortunately that is not how it works.  High fructose corn syrup does have a lower glycemic index than lower fructose corn syrups, but it is still much higher than sucrose.  High fructose corn syrup has been measured to have a glycemic index in the high 80s, which is considered fairly high.  Sucrose has a glycemic index in the high 60s, which is considered medium.  High fructose corn syrup has a significantly higher glycemic index than sucrose.  Why is this?  It is most likely because of how the molecules arranged.  In high fructose corn syrup, the glucose can be absorbed into the bloodstream almost immediately.  The fructose does still have to be processed by the liver, but this does not make much of a difference.  The fructose only slightly slows the absorption of the glucose (otherwise the glycemic index would be 100).  Because the glucose and fructose are bound in pairs in sucrose, an extra step must be taken before the glucose can be absorbed into the bloodstream.  The pairs must be broken.  This takes enough extra time to significantly reduce the glycemic index of sucrose.  Once this is done, the glucose and fructose are treated no differently from the same molecules in high fructose corn syrup, but the extra processing time makes sucrose a slower, steadier form of energy than high fructose corn syrup.

The implications of this should be clear.  Frequent consumption of high fructose corn syrup is very likely to eventually cause type 2 diabetes and may lead to heart disease.  Frequent consumption of sucrose is less likely to cause these problems, or at least will take longer to cause them.  Note that these are not short term complications.  Drinking a cup of straight corn syrup every day for a month will probably not cause type 2 diabetes or heart disease.  Drinking a liter of soda a day for 20 years will dramatically increase the risk of these diseases though (even a few cups a day may be enough).  Because different people react differently to elevated blood sugar (some may regulate insulin better than others), it is not entirely predictable how long it will take.  On average, a person who starts a high sugar diet around 10 years old will probably start showing symptoms of pre-diabetes in their early 30s and may have full on type 2 diabetes by 40, but again, each person is different.  Because it has a more dramatic effect on blood sugar, frequent consumption of high fructose corn syrup is more likely to cause these diseases, and sooner, than high sucrose consumption.

Clearly, the body can "tell the difference" between the two sweeteners.  In fact, the body can almost always tell the difference between two chemicals that have any difference, regardless of how similar they are.  Just because they are composed of similar compounds, or just because we cannot taste the difference, does not mean that the body cannot tell the difference.  It may take two or three decades before we will feel the full effects, but the body can definitely tell the difference between sucrose and high fructose corn syrup.

There is another myth that the Corn Refiners Association's lie was designed to counter.  Many people have been convinced that high fructose corn syrup contains harmful chemicals.  This is false.  While sugars may be harmful in excess, this is true of any sugar, not just high fructose corn syrup (extremely high consumption of sucrose will still eventually cause diabetes, and some links have even been found between excessive consumption of fructose and liver disease).  The point is, consuming high fructose corn syrup is not going to immediately make you sick unless you are allergic to corn.  (If drinking large amounts of soda makes you feel sick, it is probably because of the caffeine.  Of course, it could be a corn allergy, but those are fairly rare.)  In small amounts with other foods, high fructose corn syrup is entirely safe.  In general, a high sugar diet should be avoided anyway.  The best sources of sugar are fruits and vegetables.  Refined sugars are almost always easier to metabolize (read, higher glycemic index) than sugars in their original sources.  Also, refined sugars do not have significant nutritional value, which makes them "empty calories."  So, don't eliminate high fructose corn syrup from your diet because someone told you it is inherently unhealthy.  Reduce your intake because too much may eventually lead to having to stab yourself multiple time a day to avoid an early, miserable death (or, if you get hearth disease, even stabbing yourself will not prevent an early, miserable death).