Note: This article was originally posted on April 9, 2019, and was updated and reposted on November 9, 2025.
Introduction
Did you know that “complex carbohydrates” are just long chains of sugar molecules, like pearls on a string? How quickly and how high blood sugar spikes depend on what those sugars are.
This article was inspired by a graphic shared by Dr. RD Dikeman* on social media (in 2019), which shows complex carbohydrates as long chains of glucose — exactly what starches are. Not all complex carbohydrates are simply glucose chains; some are composed of other sugars and can affect blood sugar levels differently. This article explains: 1. What complex carbohydrates are 2. How they are digested 3. How different types affect blood glucose.
*Dr. RD Dikeman holds a PhD in Theoretical and Mathematical Physics and became highly knowledgeable about carbohydrate metabolism after his son was diagnosed with Type 1 Diabetes in 2013. At that time, his son was eating 40–60 grams of carbohydrates per meal and experienced large swings in blood sugar, including an episode of ketoacidosis — a dangerous condition caused by very high ketone levels due to insufficient insulin. This is different from ketosis, which is a normal state when the body uses fat for energy, such as after an overnight fast. About five years ago, Dr. Dikeman’s son began following the low-carbohydrate protocol outlined in Dr. Richard Bernstein’s book Diabetes Solution. Since then, he has been able to maintain stable blood sugar levels with the minimum necessary insulin doses.
I liked the analogy of Dr. Dikeman’s graphic and wanted to use it as a ‘jumping off point’ for this article.
Glucose — Explained Simply
Glucose (also called dextrose) is the main sugar in your blood. That’s why blood sugar and blood glucose mean the same thing. Glucose is one of two main energy sources — the other is ketones. Even people who don’t eat low-carb diets make small amounts of ketones after a night’s sleep. The body uses both glucose and ketones for energy. Carbohydrate-containing foods are broken down into glucose for energy; however, the body can also produce glucose from protein and fat through gluconeogenesis, ensuring that the brain and red blood cells always have glucose [1].
The Glucose–Complex Carb Analogy
In Dr. Dikeman’s illustration, complex carbohydrates are shown as long chains of glucose molecules — like a string of pearls. Starches are long chains of glucose; however, not all complex carbohydrates are composed of only glucose. Some carbohydrates include other simple sugars such as galactose or fructose, which the body digests differently. Other complex carbohydrates (like some fibers and oligosaccharides) contain mixed sugars that may or may not be digestible [1][2].
Simple vs. Complex Carbohydrates
Carbohydrates are often divided into simple sugars, which consist of one or two sugar molecules, and complex carbohydrates, which are made up of three or more sugar molecules linked together.
Simple Sugars
Monosaccharides
Simple sugars are called monosaccharides (“mono” means one) because they are made from a single sugar molecule.
Examples: glucose, fructose, galactose.
Disaccharides
Disaccharides are also simple sugars (“di” means two). They are two sugar molecules joined together.
Examples:
Sucrose = glucose + fructose
Lactose = glucose + galactose
Maltose = glucose + glucose
Simple sugars (monosaccharides) such as glucose break down much more quickly and, as a result, have a much quicker impact on blood sugar than disaccharides (made up of two sugar molecules) like sucrose (table sugar).
Complex Carbohydrates
Complex carbohydrates are made up of three or more sugar molecules linked together.
Oligosaccharides contain 3–10 sugar molecules and are found in beans, peas, and lentils.
Examples:
Raffinose = galactose + glucose + fructose
Stachyose = galactose + galactose + glucose + fructose
Humans cannot digest oligosaccharides; however, our gut bacteria can ferment [1][5].
Polysaccharides contain hundreds or thousands of sugar molecules. When all sugars are glucose, the polysaccharide is called starch. Polysaccharides that humans cannot digest, such as cellulose and hemicellulose, are fiber, which slows digestion and can help control blood sugar [1].
Starch
Starches are long chains of glucose molecules, strung together like a string of pearls. They are found in grains, including wheat, corn, rice, oats, millet, and barley, as well as tubers such as potatoes, yams, sweet potatoes, and cassava.
There are two types of starches: the long unbranched chains called amylose and the long branched chain ones called amylopectin.
Amylopectin is digested more easily than amylose. Cornstarch, high in amylopectin, digests faster than wheat starch, which has more amylose [1].
Since each “pearl” on the string is glucose, which is a simple, quickly absorbed monosaccharide, digestion of these starches occurs quickly, and so does the corresponding spike in blood sugar. Enzymes act to cut the connection between the glucose molecules (i.e., the “pearls”), and that “complex carbohydrate” becomes many individual simple sugar molecules.
Digestion of Carbohydrates
Digestion of carbohydrates begins in the mouth. This is where salivary amylase starts breaking starch into smaller polysaccharides and maltose. The process continues in the stomach, where the high acid environment temporarily halts digestion, then continues in the small intestine, where pancreatic amylase breaks starch into maltose (two glucose molecules). Fo
Brush-border enzymes split maltose into two glucose molecules. The enzymes sucrase and lactase split sucrose and lactose into glucose, fructose, and galactose [1][3].
Monosaccharides are absorbed into the small intestine and transported to the liver, where fructose and galactose are converted to glucose, then stored in the liver as glycogen. When glycogen stores are full, excess glucose is converted to fat [1][2]. These are quickly absorbed and, as a result, have the most immediate effect on blood sugar.
Carbohydrates and Type 2 Diabetes
As covered in previous articles, including this one, there is no requirement for people to eat carbohydrate-based food provided that adequate amounts of protein and fat are consumed [3]. In the absence of carbohydrates in the diet, fats and proteins can be used by the body to produce glucose for the brain, in a process called gluconeogenesis. This does not mean that I recommend people avoid eating carbohydrate-based food, but rather to be aware of how carbs affect their blood sugar.
People with type 2 diabetes or pre-diabetes should monitor the effect that carb-based foods have on their blood sugar. Some people do well eating legumes (pulses), including whole (not pureed) black beans, white navy beans, pinto beans, red and white kidney beans, chickpeas, and fava beans [5] because the fiber in them slows down their digestion. The reason pureed legumes have a very different effect on blood sugar than whole, cooked legumes is covered in this earlier article, under the header “The Effect of Mechanical Processing on Blood Glucose Response”.
The effect of simple sugars and starches on blood sugar is very different, because they are simply a string of “pearls”, where the pearls are glucose and easily split during digestion.
Personalized nutrition is key. “Eating to your meter” helps those with type 2 diabetes test how specific foods affect their blood sugar [4].
Final Thoughts
Carbohydrates are just strings of pearls, where the pearls are sugar molecules. Starches are made up of only glucose molecules, which are easily split apart during digestion, resulting in large amounts of individual glucose molecules that quickly spike blood sugar.
Legumes (pulses, beans) eaten whole (not pureed, which speeds up their digestion and results in a spike in blood sugar) and in small portions are digested more slowly and less likely to spike blood sugar. Monitoring the effect of food on blood sugar is essential for those with type 2 diabetes or those with pre-diabetes and for those at risk.
Personalized nutrition focuses on customizing your diet — the types of foods, portion sizes, and timing — to meet your specific health needs, and it is at the heart of the routine services that I offer.
For more information, please visit the Services tab above.
To your good health,
Joy
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References
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Chapter 4, Carbohydrates: Simple Sugars and Complex Chains, http://samples.jbpub.com/9781284064650/9781284086379_CH04_Disco.pdf
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Rappaport B. Metabolic factors limiting performance in marathon runners. PLoS Comput Biol. 2010;6(10). doi:10.1371/journal.pcbi.1000960 [https://journals.plos.org/ploscompbiol/article?id=10.1371/journal.pcbi.1000960]
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National Academies Press. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. 2005; Chapter 6, pp. 265–275. [https://www.nationalacademies.org/projects/HMD-FNB-18-P-119/publication/10490]
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Zeevi D, Korem T, Zmora N, et al. Personalized Nutrition by Prediction of Glycemic Responses. Cell. 2015;163(5):1079-1094. [https://pubmed.ncbi.nlm.nih.gov/26590418/]
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Sievenpiper JL, Kendall CWC, Esfahani A, et al. Effect of non-oil-seed pulses on glycaemic control: systematic review and meta-analysis. Diabetologia. 2009;52:1479. [https://pubmed.ncbi.nlm.nih.gov/19526214/]
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