Deconstructing Sugar

Sucrose, fructose, glucose:  What’s the difference?

 

How do you sweeten your tea or coffee (if at all)?  Table sugar, honey, agave, etc.?  In order for your body and brain to function properly you absolutely need glucose for energy.  Although your body has the enzymatic machinery to make its own glucose this can be somewhat of an arduous task. Immediate demands for energy can be met by the sugars that you eat.  Back in my day the only sugar in my Mom’s pantry was white Table sugar. 

The sweetener in Table sugar is sucrose, a disaccharide composed of fructose and glucose in equal proportion.  A brief walk down the baking aisle of your local supermarket today will avail you to a much larger variety of sucrose containing sweeteners (Table 1):  Brown sugar, confectioner’s sugar, evaporated cane juice (or raw sugar), maple syrup and molasses.  All the same thing but dressed differently.  Corn syrup, on the other hand, is composed entirely of glucose while Agave is largely composed of fructose.  Sweeteners composed of individual fructose and glucose monosaccharides include high fructose corn syrup, honey and invert sugar (used in making candies and fondant which require a smoother product). 

Both glucose and fructose provide energy but the process to do so differs.  Glucose readily passes through the gut barrier into the bloodstream and provides instant gratification to meet your energy demands.  It is the sugar that powers your muscles to give you strength, and your brain so that you can think.  Fructose, on the other hand, requires assistance from a transporter called GLUT5.  Once absorbed in the gut, fructose is processed by the body and stored in the liver as a back-up energy source called glycogen.  Your liver has the capacity to store roughly 2000 calories of sugar.  Excess sugars, above this amount, are converted to lipids and stored in fat cells which have an infinite storage capacity.  This is largely why consumption above and beyond what the body needs, leads to obesity.

An excess of fructose has a number of additional adverse effects as well.  Excess fructose can swamp GLUT5, preventing its absorption.  Fructose that remains in the digestive track serves as a feast for bacteria residing in the gut.  The bacteria will ferment the fructose giving off a variety of gases such as hydrogen, methane, carbon dioxide and hydrogen sulfide which contributes to feelings of bloating, distention, bowel discomfort or abdominal pain.  Furthermore, as the excess fructose travels along the bowel it also draws along with it excess water, which has a laxative effect on the bowel, causing diarreah.

In addition, excess fructose, along with excess glucose, can overwhelm the liver’s capacity to store sugar and to regulate insulin secretion.  Insulin is a hormone produced by the pancreas that tells the body to take glucose out of the blood and deliver it to muscles and other body tissues so that they can function properly.  Carbohydrate and sugar-laden diets ultimately disrupt the ability of the pancreas to make enough insulin to support energy demands or, despite an ample insulin supply, the body loses its ability to respond to insulin, both of which are hallmark features of type 2 diabetes.  While insulin serves a critical role in energy production, excess insulin, either secreted by the pancreas or taken by injection if you are Diabetic, will eventually lead to a host of metabolic and inflammatory conditions.

Fructose found in fruit and vegetables deserves special attention. Soluble fiber that is naturally found in these foods slows the absorption of fructose and subsequent spike in insulin.  Not only are these foods healthy for you but they are also healthy for the bacteria in your gut.  And when you take good care of the bugs in your gut, they will take good care of you.  Benjamin Franklin definitely was on the right track when he said “An apple a day keeps the doctor away”.

 

Table 1.  Composition of Sweeteners