To Carb or Not to Carb?!
By: Jared Miller
To carb or not to carb? This is a question that receives considerable attention when discussing subjects of nutrition, and is often a subject of argument between many. With so many different opinions being expressed, it can be hard to know for sure what is really true. This article will attempt to explain some key concepts regarding carbohydrates and nutrition, in a way that does not force an opinion. Instead, it will allow readers to think for themselves and develop their own opinion by educating themselves on concepts that are regarded as being factual by most authorities.
For a relatively detailed overview of carbohydrates that will be important for those who are really motivated to take control of their eating habits, read the whole article. For some general guidelines for those who may not have the time, begin reading at General Recommendations.
Carbohydrates, commonly referred to as ‘carbs’, are a type molecule found in most living organisms. In animals, carbohydrates are often in the forms of glucose and glycogen. Glucose is a monosaccharide, meaning it is a singular carbohydrate molecule. Glycogen is a polysaccharide, meaning it is a carbohydrate made of many molecules. Notice the names of these sugars. The suffix ‘ose’ denotes a sugar; and the prefix denotes the type of sugar. For illustration purposes, consider the word lactose. The prefix ‘lact’ refers to milk, and ‘ose’ refers to sugar, because this type of sugar is found in milk. Also, the prefix “glyco” refers to sugar; it is derived from the Greek word for ‘sweet’. Therefore, glyco-gen is ‘glucose generating’. Many ‘scientific’ terms are formulated according to this method, and once that is understood, it becomes much easier to understand scientific literature.
Glucose and Glycogen
There are two main forms of carbohydrates in the human body that are particularly important when learning about nutrition. They are known as glucose and glycogen, and they perform different roles.
The Role of Glucose
Glucose is the simple form of sugar found in cells of the body, as well as extracellular fluids such as blood, and it is vital to human function. After a meal, carbohydrates that were absorbed by the small intestines travel to the liver for processing before distribution to the rest of the body through the bloodstream. The neurons (brain cells) virtually always function on glucose as a fuel source, and therefore, require a steady supply of glucose to function normally. Similarly, glucose is the only fuel source that red blood cells can use for energy. Notwithstanding, carbohydrates are a fuel source for working muscle cells during activities such as hockey, running or lifting weights, but muscle cells, along with most cells in the body, do not need carbohydrates as a fuel source. Nonetheless, considering that the brain and blood need glucose to function, it is possible to establish that there is at least a minimum amount of carbohydrates that need to be consumed in the diet.
The Role of Glycogen
Glycogen is a form of carbohydrate that is found in human muscle cells, as well as the liver. Glycogen is comprised of many (thousands) of glucose molecules in a branching, chainlike structure. Glycogen is a storage molecule that can be catabolized (broken down) into glucose, to provide fuel to the muscle cells during exercise. Glycogen is similarly catabolized in the liver and released into the blood for the purpose of maintaining blood sugar levels between meals.
The important fact to remember is that the muscles and the liver both have a limited capacity to store glucose as glycogen. Which means that a surplus of carbohydrates in the diet will get converted into triglycerides, packaged into VLDL (very low density lipoprotein) and transported out to the adipose (fat) tissues to be stored as fat. After this, the VLDL becomes LDL (low density lipoprotein). Consistently high levels of these blood particles can contribute to the development of ‘plaque’ in arteries when they eventually become oxidized. By knowing these facts, it is possible to establish that is also an upper limit to the amount of carbohydrates that should be consumed in the diet.
A Goldilocks Zone
It seems that carbohydrates are a very important nutrient considering that the brain and the blood cells need glucose to function and therefore too little of this nutrient can be problematic. Conversely, too much of this nutrient can also have a negative effect on the body, by increasing VLDLs and LDLs in the bloodstream as well as the accumulation of excess body fat. All of this lends evidence that there is a range of carbohydrate intake that is appropriate for healthy functioning of the human body.
Brief Overview of Sources of Carbohydrates
Plant sources of food such as vegetables, fruits and whole grains are going to be the main sources of carbohydrates in a health promoting diet. There are three fundamental forms of carbohydrates in plants: simple sugars, complex starches and fiber.
Sugars come in multiple forms as described earlier in the article. One of the most important things to remember about sugars is that they are simple forms of carbohydrates that are easily absorbed into the bloodstream through the digestive tract, and therefore, are likely to have the greatest effect on blood sugar levels in comparison to other nutrients.
Starch (scientifically named amylose) can be considered the plant’s equivalent of glycogen because it also a polysaccharide composed of repeating glucose subunits. When consumed in the diet, starch is catabolized into smaller units that eventually become glucose. These glucose molecules are then absorbed into the body.
Fiber is the name given to the indigestible carbohydrate that forms the cell walls in plants. Fiber does not contribute any Calories to the diet. Since fiber does not get digested, it travels through the digestive tract to be excreted in the stool, which is a very important reason why vegetables, fruits, and whole grains promote a healthier digestive system.
Brief Overview of Properties of Carbohydrates
Being informed on some of the types of carbohydrates, it is possible to begin to introduce the concepts of the glycemic index and glycemic load. These values are influenced by the physical properties of the source of carbohydrate. Different sources of carbohydrates have different glycemic scores. Generally, the more complex the carbohydrate, the longer it takes to digest and absorb, giving it a lower glycemic score. Foods with low glycemic scores will create the smallest increases in blood sugar and insulin levels. The simpler the carbohydrates, the faster it is digested and absorbed, giving it a higher glycemic score. Foods with high glycemic scores will create the greatest rise in blood sugar and insulin levels. However, there are exceptions to this rule. For instance, compare white rice (a grain composed mostly of complex starch) with a pear (a fruit containing sugar, starch and more fiber).
|Food||Glycemic Index||Glycemic Load||Serving size (g)|
|White rice, average||90||43||150|
(Atkinson, F., Foster-Powell, K. & Brand-Miller, J., 2008)
By applying the concept of glycemic index and glycemic load to daily food choices, each meal can be appraised for its likely affect on blood sugar and insulin levels, allowing one to make wiser food choices. Typically, more fiber in a food will influence it to be lower on the glycemic scale, slowing down the time it takes to digest the sugars and starches. Fiber in a food is comparable to the tape, ribbon and wrapping paper on a present; it slows down the process.
In general, people who are overweight would benefit from a lower proportion of carbohydrates in their diet, by eating lots of vegetables in place of grains and fruit. Vegetables that grow above the ground such as broccoli, cauliflower, spinach, kale, Swiss chard, brussels sprouts and cabbage among other vegetables are great because they have lots of fiber, but low levels of starch and sugar. Root vegetables that grow below the ground are also very healthy choices, and are one of the best sources of carbohydrates in the diet because they tend to have low glycemic scores. People who crave carbs would benefit from eating root vegetables in place of the typical foods that people eat to fulfill cravings. Eating in this manner will help to keep blood sugar levels more stable and closer to the normal range, which is of great benefit to people who are obese, people with type II diabetes mellitus or heart disease (all of these conditions are associated with each other).
In general, currently lean individuals or those who have achieved a healthy bodyweight should still be eating lots of vegetables that grow above ground, while choosing to consume root vegetables and fruits depending on their activity level. Eating in this manner will help to keep blood sugar levels closer to the normal range, and prevent storage of excess body fat.
Here are some principles to help guide choices of carbohydrate intake:
- The more overweight the individual, the more they should limit sugar and starch intake, with a focus on consuming fibrous above ground vegetables.
- The more overweight the individual, the more sugars and starches will raise their blood sugar levels and keep them elevated longer, which is a contributing factor in the development of pre-diabetes and type II diabetes.
- The more overweight the individual, the less they can afford to make poor food choices, due to relatively more cumulative effects of high blood sugar, and subsequently more VLDL and LDL cholesterol in the blood vessels.
- The leaner the individual, the more they can consume carbs in the diet with relatively less cumulative effects of high blood sugar.
- The more muscle mass the individual has, the more they can consume carbs in their diet in accordance with the principles stated above.
- In both populations, the higher their activity levels, the more they can tolerate carbs in accordance with the principles stated above.
- In both populations, aim to eat foods with a low to moderate glycemic index and load.
- In both populations, do not be distressed if you do not strictly follow the ‘rules’ of healthy eating. The effects of that can be worse than the poor food choice. The key is making an honest effort to do your best.
It is safe to say that carbohydrates are important nutrients that participate in vital human functions. The key to carbohydrate consumption is eating according to needs for energy, keeping in mind that carbs are fuel. If there is little to no activity to burn up that fuel, you don’t need to keep filling the gas tank (muscle and liver glycogen stores) with carbs.
It is clear that there are many factors to consider while choosing the right sources of food to eat. The details are good to know and can allow someone to make food choices that are deliberate and informed. However, the details are not all that necessary if a person eliminates consumption of processed foods, drinks at least 1.5L of water per day, and eats a diet of wholesome foods in their recognizable form; namely a colourful variety of vegetables, various meats and fish, eggs (think beyond the chicken), nuts and seeds in their many varieties, and plain dairy products (think beyond the cow). A diet of this nature is a health promoting diet, which will help you reach your potential in all aspects of life!
Atkinson, F. S., Foster-Powell, K., & Brand-Miller, J. C. (2008). International tables of
glycemic index and glycemic load values: 2008. Diabetes care, 31(12), 2281-2283.
Whitney, E., & Rolfes, S. R. (2007). Understanding nutrition. Cengage Learning.