All too often I hear people say that they have cut all carbohydrates out of their diet. This always prompts me to ask – even fruits and vegetables? They usually look at me as though I am crazy, and tell me that they mean bread, pasta, and other grains.
Carbohydrates have had plenty of press time in the last few decades thanks to some popular diet fads. Despite this, many people still do not understand what carbohydrates actually are, and why our bodies need them. And given all of the misinformation in the media, it is not surprising.
So what exactly are carbohydrates? And what do we mean by simple, complex, and refined?
Carbohydrates are compounds consisting of either single or multiple sugar units.
Simple carbohydrates are made from either one sugar unit, or two sugar units linked together.
Simple carbohydrates include sugars found naturally in foods (such as fructose in fruit and lactose in milk), and sugars added during processing or preparation of foods (such as table sugar in coffee or high fructose corn syrup in sugar-sweetened drinks).
Complex carbohydrates are long chains of sugar units that form either starch or fiber.
Starch is made up of thousands of glucose molecules in long strands. It is the way plants store glucose. When we eat the plant, we break the starch down into individual glucose molecules and use them primarily for energy. Foods containing starch include:
- Grains (such as rice, oats, wheat, barley, corn, rye, millet, and buckwheat)
- Beans and peas ( such as garbanzo beans, kidney beans, lentils, and split peas)
- Tubers (such as potatoes, carrots, beets, and parsnips)
- Refined starches added to food as thickeners and stabilizers (such as corn starch)
Fiber is also composed primarily of long strands of glucose molecules. However, unlike starch, the glucose molecules in fiber cannot be broken apart by human digestive enzymes. Therefore most fiber passes through the human digestive system without providing any energy. Instead, fiber helps maintain healthy bowel function, keeps blood cholesterol levels down, and helps modulate blood glucose levels. Fiber also helps us feel full after a meal, thereby stopping us from eating too much food.
Refined carbohydrates are those that have had the coarse (and nutritious) parts removed.
A whole grain kernel has four parts:
- Germ – the inner part of the grain that is rich in nutrients
- Endosperm – the main starchy part of the grain
- Bran – the fibrous coating that protects the grain, where most of the fiber lives
- Husk – the inedible outer part of the grain
When we eat whole grains, we eat the first three parts, including the nutrient-rich germ and the fiber-rich bran. Refined grains, on the other hand, have had the husk, bran, and germ removed to leave only the starchy endosperm. While many people think it makes for a more pleasing texture and taste, refined grains are devoid of many of the healthy nutrients and fibers contained in whole grains.
Even when refined grains are enriched to have some of the nutrients put back in, they are still not nutritionally equivalent to whole grains. When you choose refined grains over whole, you are depriving your body of the healthy nutrients and fiber that were once part of the grain.
In addition, the starch in refined carbohydrates can be broken down to glucose more rapidly than the starch in unrefined carbohydrates. This results in a faster release of glucose into the blood stream.
Should I be eating carbohydrates?
Glucose is the preferred energy fuel for the human body, especially the brain and nerves.
Glucose contains six atoms of carbon. Those six atoms are held together by chemical bonds. Those bonds are made from the sun’s energy during the process of photosynthesis in green plants (remember back to those school science classes?) That energy from the sun captured in carbohydrates is what our body uses to drive the processes that allow us to live.
In the absence of glucose, the human body will encounter two problems:
- It will use protein to make glucose. This is a problem because excess protein is not stored in the body. Therefore, in the absence of glucose for energy, the body will divert blood, organ, or muscle proteins from their own crucial functions to be converted to glucose.
- It will try to use fat for energy, resulting in the production of acidic, fat-related compounds called ketone bodies. Ketone bodies accumulate in the blood causing ketosis. Eventually the levels of ketone bodies in the blood can get high enough to disturb the acid-base balance in the body, with many potential negative health consequences.
Does it matter which carbohydrates I eat?
Naturally occurring unrefined complex carbohydrates, particularly those rich in fiber, are the best source of glucose in our diet.
Unrefined complex carbohydrates contain vitamins, minerals, fiber, and phytochemicals that are all extremely beneficial to health. With complex carbohydrates, the human body has to take the time to break down the long strands of glucose, thereby slowing its release into your blood stream, unlike simple carbohydrates. In addition, the fiber contained in most unrefined complex carbohydrates slows down the movement of food from the stomach into the intestine (gastric emptying). This also helps slow the release of glucose into the blood, and helps maintain a feeling of fullness after a meal.
The simple carbohydrates found in fruit (fructose) are also great to include in your diet, as fruit contains many other healthful compounds including vitamins, minerals, and antioxidants.
Refined carbohydrates and foods with added sugars, on the other hand, are not such a good source of carbohydrates and should be limited.
So what should you actually eat?
- Whole grains, such as whole grain bread, whole grain pasta, whole grain rice
- Legumes, such as beans, peas, and lentils
And what should you limit/avoid?
- Refined grains, such as white bread, white pasta, white rice
- Added sugars, such as those in sugar-sweetened drinks, cereals, and other processed foods.
How many carbohydrates should I eat per day?
The Dietary Guidelines for Americans 2010 recommend that carbohydrates should provide between 45% and 65% of daily calories for children and adults.
For someone eating 2,000 calories a day, that equates to between 900 and 1,300 calories a day from carbohydrates, or 225 to 325 grams of carbohydrates per day.
For someone eating 2,500 calories a day, that equates to between 1,125 and 1,625 calories a day from carbohydrates, or 281 to 406 grams of carbohydrates per day.
The Institute of Medicine states that, at a minimum, all adults and children should consume at least 130 grams of digestible carbohydrates per day (i.e. not including fiber) to make sure the brain gets enough glucose.
Carbohydrate content of common foods
What does that mean in real terms? Listed below are the approximate carbohydrate contents of some common foods. You can find the carbohydrate content of more foods on the United States Department of Agriculture National Nutrient Database.
1 slice of bread (white or whole wheat) – 15 grams
1 plain bagel – 50 grams
1 8” flour tortilla – 25 grams
1 cup cooked oatmeal – 30 grams
1 cup cooked brown rice – 45 grams
1 cup cooked white rice – 53 grams
1 cup whole wheat spaghetti – 37 grams
1 average corn-on-the-cob – 15 grams
1 medium baked potato with skin – 37 grams
1 cup canned, drained garbanzo beans – 35 grams
1 cup canned, drained red kidney beans – 33 grams
1 cup canned, drained black beans – 40 grams
1 medium apple – 25 grams
1 medium banana – 27 grams
1 cup sliced strawberries – 13 grams
1 medium peach – 14 grams
The bottom line
- Carbohydrates are the preferred energy source for the human body.
- Eliminating carbohydrates from your diet entirely is not a good idea.
- Carbohydrates should account for 45 to 65% of your daily calories.
- Naturally occurring unrefined complex carbohydrates, particularly those rich in fiber, are the best source of glucose in your diet.
- The best sources are whole grains, legumes, fruits, vegetables, and milk.
- Refined carbohydrates and added sugars should be limited.