Are sugars good food?

"Eat low GI food"!  "LowCarb diets cure overweight"!  "Eat fat"! "Watch out for sugar bombs"! The daily press is full of articles telling us what to eat.  Is there anything in these claims?  Is bread really "bad food"?  Are potatoes really safe? Do we need to eat sugars at all? 

The answers are really quite simple.  Our genetic makeup seems to say that we should eat a good portion of sugars and starch daily.   We must use carbohydrates to supply the energy needed to drive our bodies.  Our brain, the retina of the eye and red blood cells have glucose as their only energy source. 

In spite of this, we can survive quite well without eating sugars and starch.  We can make glucose ourselves!  For example, people can survive for a long time just by eating pemmican, a mixture of lean meat (proteins) and fat.  A Norwegian explorer, Helmer Hansen, gave some striking examples of this in his book about the "Gjøa" expedition under leadership of Roald Amundsen.  He wrote: "they (the Eskimos) valued only meat. Coffee made them sick, candy and chocolate were too sweet for their taste.  They did not like bread.  They ate a little of our food after staying with us for a while, but their stomachs did not tolerate this.  They were "cured" by eating meat so rotten that even the dogs would not have it".  Nevertheless, everybody (even Eskimos) must have a stable supply of sugar in their blood.  Our brains are completely dependent on  blood sugar.  Neither fats nor proteins can be used by the brain!   Hard work uses almost only sugar for energy. 

You can choose not to eat sugar.  That's OK.  But then your liver has to make sugar for you.  It can convert the meat you eat to sugar!  And, if you just do not eat you will use your own body's muscles as a source of blood sugar.  No sugar, no life! 

So, which carbohydrates should we eat?  

This puzzle is also easy to answer.  While we can choose among an almost endless variation in the protein or fatty components of our diet, the choice of carbohydrates is quite limited.  Regardless of which food we choose, there are basically only three energy-giving carbohydrates that we can digest; starch, sucrose and lactose.  And, of course, a little fructose and glucose from fruits. 

The secret is choosing food that satisfies our appetite and gives enough energy for growth and work.  At the same time we should not eat too much.  Too much food = overweight!  The best carbohydrate-rich foods are whole-grain breads (thick slices!), cooked and baked potatoes, rice, corn and pasta.   Things that satisfy your appetite and that take time to eat.  Your body needs that time to find out that your hunger is satisfied!   Good food is bulky and takes time to devour!  "Fast-food", candy and especially soft drinks give us too much food too fast.  It is far to easy to take in that "extra food" with those choices. 

And, which foods shouldn't we eat so much of?     

That's easy.  Candy, soft drinks, ice cream, syrup on pancakes...  Sure, they taste good but too much food too fast is not good for us.  Remember, many of the illnesses that are common among adults follow overweight.   And, overweight is VERY difficult to be quit.

What about table sugar?

Table sugar (sucrose) is merely a combination of glucose and fructose while milk sugar (lactose) is made up of glucose and galactose.  Starch and glycogen (animal starch) are simply glucose polymers.  Glucose is the only breakdown product of these huge molecules.  NO OTHER CARBOHYDRATES CAN BE DIGESTED AND ABSORBED BY HUMANS!  All the "others" wind up in the large intestine as energy sources for bacteria. If more than five grams daily end up there the result is often "explosive" diarrhea. 

What happens if you eat more table sugar than you can absorb?   Ask a kid who has eaten too much candy!  Eating more sugar than one can digest and take up in the small intestine leads to "stomach pain" when it is carried to the large intestine.  The bacteria in the large intestine take over with generation of lots of gas as a result. 

We are not used to eating a lot of fructose: 

Limited amounts of fructose are found in many fruits.  Honey is super-sweet, containing about 40% fructose and 30% glucose.  It used to be a scarce but real treat in earlier years. 

We have "always" eaten some fructose, but not nearly as much as we do today.  Fruit and especially honey were certainly delicacies in the past.  Even bears crave sweets and let themselves get stung while they steal honey.

Fructose became a major energy source with  development of the sugar industry and has been a key dietary component for less than 200 years.  Table sugar (sucrose) has now been partially replaced by a new and inexpensive sweetener.  This is called  “high fructose corn syrup” or "HFCS".  This is made from corn starch. This starch is chemically split to glucose and some of this is then converted to fructose.  These simple sugars are then blended in an approximately 50-50 mixture. HFCS is an inexpensive replacement for sucrose and is used to make ice cream and soda pop.  In the USA, sucrose consumption has been reduced during the past decade or two by replacing it with inexpensive HFCS.  However, HFCS is a form for sugar!  The total sugar consumption in the USA has increased because of the use of high fructose corn syrup.  Total sugar consumption in the USA is now close to 60 kg per person per year.

Each sugar has its own metabolism.

Our body is driven by energy from fats and glucose.  However, some important tissues, namely the brain and blood cells, can only use glucose as their energy source.  A stable blood sugar level is an absolute requirement for good health.  Blood sugar (or glucose) comes from starch, from proteins and from the sugar we consume.  In addition, we store a kind of starch (called glycogen) in our liver and this helps to stabilize blood sugar levels.

Around 25 % of the energy in our modern diet comes from table sugar, and half of that is fructose.  This is a new situation. Earlier, most of the "sugar" we used came from digestion of starch and our own production of sugar from proteins. 

Now, most of us utilize fructose quite well; too well in fact.  The problem with fructose is that fructose metabolism goes twice as rapidly as that of glucose.  There are no major control posts in fructose metabolism.  This is in contrast to glucose metabolism. Glucose "burning" is carefully adjusted to replace energy that is used in work and play.  If a muscle doesn't work it will not use glucose.  When the muscle begins to work, it begins to use glucose.  Fuel consumption is linked to work when we talk about glucose!  But that is not the case for fructose.  If it comes to the liver it will be used!  Even if we do not need its energy.

Look at the next drawing.

Let's take up glucose first.  It begins its metabolism by being split to two smaller compounds, pyruvic and lactic acids.   That pathway is controlled so that use of glucose balances the need for energy.  We have a "controller" who coordinates traffic on that pathway. Those two small acids are then "burned" or oxidized to CO₂.  Once again, we see that we have a "controller" here that makes sure that the supply of and demand for energy are balanced. 

These processes are very carefully controlled by various hormones.  As long as we do not take in excess glucose over time, little fat is made from this sugar. 

The same pathway is used by galactose.  This sugar must be converted to glucose before it can be "burned".  Therefore, we have good control over metabolism of milk sugar.

Fructose metabolism, on the other hand, goes very quickly and without "controllers".  And, when production of the small acids from fructose exceeds their use (burning to carbon dioxide), they are converted to fat.  Fructose is a very good source for too many calories and may well be fattening.  

Perhaps even more important is the fact that, unlike glucose, fructose does not cause release of the hormone insulin from the pancreas.  Now, insulin has many functions and one of these is to dampen appetite.  That means that half of the sugar we eat gives no "satisfied" signal to the brain.  As we all know, we can drink a lot of soda pop without feeling full. 

Can it be that fructose is to blame for the rapid increase in overweight seen during the past twenty years? 

Fructose has been suggested to be a good replacement for table sugar as a sweetening agent.  After all, it tastes two to three times as sweet as sucrose (table sugar).  So, they say, "we can have just as sweet food with much less sugar if we use fructose". 

There are two things that are wrong with this.

 1. While it is quite true that fructose is sweeter than table sugar (sucrose) this applies only to cold fructose.  If you warm it up in tea or coffee or bake it in a cake it changes form.  The sweet "5-ring" characteristic for fructose changes to a "6-ring" when fructose is warmed up.  That "6-ring" is not sweeter than sucrose!  So, coffee, tea and cakes sweetened with fructose need to have just as much fructose as usual sugar to taste "sweet enough".

2.  That metabolism bit is important.  We seem to make more fat out of fructose than other sugars.  People who drink a lot of soda pop and often eat candy tend to be overweight.  They often have increased fat levels in their blood.  This is thought to lead to development of high blood pressure and to heart disease.  Fructose may be a natural food for us, but at much lower levels than those we experience today.  Over-eating fructose lie back of the marked increase in heart disease and diabetes we see around the world today.