Tuesday, June 28, 2011

The Life of A Carbohydrate

The last decade has not been kind to the carbohydrate.  We've heard that carbohydrates make us fat, they cause the 3 pm "crash", give us diabetes, and according to some, may not even be necessary.  That's quite a list of offenses for one major component of the Big Three Macronutrients (protein, fat, and carbohydrates)!  It sounds like carbs are out to kill us!  What exactly did carbohydrates do to earn this ignoble reputation?

The answer is neither short nor easy.  We'd need to take a look at modern farming, advertising, fast food, emotional eating, and processed foods to understand the full scope of this complex issue.  That's a lot of information.  So, let's start at the beginning.  The best way to discover the truth about carbohydrates is to first understand what carbohydrates do when they enter the body, and how the body reacts in the presence of this four-calorie wonder.

What Is A Carbohydrate?

A carbohydrate is a chemical compound of carbon, hydrogen, and oxygen.  Hydrogen and oxygen are usually present in a 2:1 ratio (H2O), hence the “hydrate” suffix.  They are classified as either simple or complex based on the number of simple sugars in each molecule.  Carbohydrates include sugars, glycogen, starches, dextrin, and cellulose (indigestible plant fiber).

Simple carbohydrates contain either one or two simple sugars bound together.  A monosaccharide contains one simple sugar.  Fructose (fruit sugar), glucose (“blood sugar”), and galactose (milk sugar) are each examples of a monosaccharide.  Disaccharides contain two simple sugars, and include sucrose (fructose + glucose) and lactose (glucose + galactose).

Complex carbohydrates, or polysaccharides, contain three or more simple sugars bound together and include starches and fiber.

How Do Our Bodies Use Carbohydrates?

Our bodies can only absorb monosaccharides (fructose, glucose, and galactose), therefore, we must break down di- and polysaccharides into simple sugars.  From our stomach, they enter the small intestine and then the portal vein.  The portal vein leads to the liver, the location in the body where simple sugars become glucose and then enter the bloodstream.

When glucose enters the bloodstream, the body uses it in one of three ways:

1.      It is burned immediately for energy if blood glucose levels are not stable at 20 grams of blood glucose circulating per hour.

2.      If the body’s energy needs are not immediate, the pancreas releases insulin which converts glucose into glycogen.  The glycogen is then stored as energy reserves in the brain, muscles, and liver.

3.      If glycogen stores are adequate in the brain, muscles, and liver, and there is an excess of glucose, the liver converts the excess glucose into fat.  The fat is stored as triglycerides (blood fat), cholesterol, and adipose tissue (body fat) around the body.  If needed, these fatty tissues can be burned for energy as fatty acids, but they will not be converted back into glucose.

Why Is Fiber Important?

Fiber is a carbohydrate that comes from plant matter.  It is either soluble, which means that it dissolves and enters the blood stream, or insoluble, which means that it remains in the digestive tract.  Both types of fiber are important for maintaining health, but are not sources of energy. 

As soluble fiber moves through the blood stream, it binds to the fatty acids that would turn into LDL cholesterol (the bad stuff).  The soluble fiber + pre-cholesterol is then treated as waste and removed from the system, preventing the synthesis of cholesterol.  A diet rich in soluble fiber may reduce cholesterol by preventing its synthesis. 

Insoluble fibers like cellulose serve two purposes in the body.  They help keep the digestive tract regular by moving bulk through the intestines.  Because it helps insoluble bulk move faster, it prevents some starches from breaking down and entering the blood stream.  Insoluble fiber is important for people losing weight because it does not dissolve, so they will feel full longer, and it helps prevent starches from converting into sugars, thereby regulating blood sugar and insulin levels. 

What Are The Glycemic Index and Glycemic Loads of Foods?

The Glycemic Index (GI) refers to the relative degree to which blood sugar increases after the consumption of food.  Foods are given a value which relates to the amount blood sugar increases in comparison to pure glucose (100).  For example, a raw apple is assigned at GI value of 40.  This means that when you eat a raw apple, your blood sugar will increase only about 40% as much as it would if you consumed pure glucose.

The Glycemic Load (GL) of food refers to the carbohydrates and portion size of a food.  A food higher in carbohydrates like watermelon is assigned a low GL because of its small portion size.

The University of Sydney maintains a comprehensive database of common foods.  You can find the link here.  You can search for food by name and by GI and GL values.

The Harvard School of Health recommends consuming foods with GI values of 55 or below and GL values in the low teens.  While there is much controversy over the value of a diet based on the GI and GL foods, there are a few points that many will agree are universal in the goal to eat more healthfully.

·         Make the switch from:

o   Instant or white rice to basmati or brown, or quinoa, spelt, or slow-cooking barley
o   Instant oatmeal to steel cut or old fashioned oats
o   White bread to whole grain, sprouted grain, or stone ground bread
o   Canned fruits and vegetables to fresh
o   Boiled vegetables to lightly steamed or raw

With respect to grains, a good rule of thumb came from a friend’s nutritionist, “The longer a grain needs to cook, the longer it takes to digest.”

Using the GI and the GL as a tool can help you choose foods which will aid in losing weight or maintaining good health. 

Putting It All Together

Carbohydrates are a necessary and vital part of our daily diet.  As we’ve discussed earlier, the general rule is that carbohydrates should make up approximately 50% of your daily caloric intake.  People with insulin resistance and diabetes may require less, while endurance athletes may require more.  Carbohydrates turn into glucose, which can be burned immediately, or synthesized into glycogen, the fuel that moves our bodies.  When glycogen levels are at full capacity in our brain, muscles, and liver, only then is excess glucose stored as fat.  The source of the simple sugar is irrelevant with respect to the body’s response to glucose.  People with more muscle mass store more glycogen than people with less muscle mass.

Soluble and insoluble fibers are carbohydrates which the body cannot use as fuel.  Soluble fiber helps prevent the synthesis of LDL cholesterol, while insoluble fiber prevents starches from converting into simple sugars and entering the blood stream.  By keeping the digestive tract regular, insoluble fiber regulates blood sugar levels and insulin secretion.

The Glycemic Index and Glycemic Loads of Common Foods are useful guidelines for people looking to improve dietary choices.  Switching to diets rich in carbohydrates from whole, unprocessed grains, fruits, vegetables, and beans will aid in weight loss.  As with all dietary recommendations, portion control is essential.  While these foods are extraordinarily rich in fiber, vitamins, and minerals, consistently consuming excessive portions is counterproductive to the goal of maintaining good health.

Consuming reasonable amounts of carbohydrates won’t make us fat or unhealthy.  Eating too many unhealthy carbohydrates too often leads to increased body fat, high cholesterol, excessive triglycerides, heart disease, high blood pressure, and increases the risk of developing Type 2 diabetes.  Yet, in the journey back to good health, carbohydrates are an ally.  We’ve learned that the body uses a mix of glycogen and fat to move us, to fuel us, to make us GO!  This means that fat burns constantly in the presence of carbohydrates!  Maintaining regular blood sugar levels will allow your body to burn fat regularly and efficiently throughout the day and can help prevent the onset of diabetes.  You’ll give your pancreas a break when you require less work from it.  Additionally, your energy levels will neither peak nor plummet when you eat regularly.

At a mere four calories per gram, carbohydrates really are the Four Calorie Wonder.

Source: Fitness: The Complete Guide. Fredrick C. Hatfield, Ph.D. International Sports Science Association, Carpinteria, CA. 2010




Anonymous said...

Thank you for this great article. In two weeks I will be riding my bike in a two day 200 mile trek (Seattle to Portland, or STP). I'm not doing well to regulate my food intake during my long practice rides. I've been eating trail mix, but I think I need more carbs. Do you have any articles about nutrition for endurance activities?

Anonymous said...

Hi Dave,

I haven't written any articles on endurance nutrition specifically. However, I'd recommend searching the active.com and livestrong.com blogs for endurance nutrition information. I just stumbled on the Ultra Marathon Cycling Association's webpage and it's loaded with nutrition information. Best of luck! What an amazing adventure! PLEASE let me know how it goes! http://www.ultracycling.com/nutrition/nutrition.html

Anonymous said...

Sorry, that was Natalie. Blogger's not letting me post comments. Ha!

Trina said...

Natalie I canot find anything I can stick too. I use to do a very low carb and lose weight but binge after a month and gain it all back. Then I try counting calories and that works more slowly but then im inconsistent with my logging so i don't lose. I cant even find a way of exercising that im willing to commit to. But i hate my body and im tired all the time and i know its because of the weight. Im only 33 yr old and 5ft and 197 lbs. I would like it if we could see what a days food will be like to lose 1 to2 lbs a week looks like without getting food none wants to eat. I think i have to use these pictures i took of my body as motivation. But they may put me into depression and that would be a next issue.