Plant carbohydrates: what to know about them in food
Plant carbohydrates are an everyday staple: potatoes, bread, porridge, fruit and many vegetables provide your body with energy every day. Plant carbohydrates do not automatically mean sugar. They are a large group of substances that includes rapidly absorbed sugars as well as starch and dietary fiber. Understanding the differences makes it easier to eat in a way that keeps you full and your energy levels steady.
Why do plant carbohydrates matter?
The term “carbohydrates” came into use because many compounds in this class can be regarded as hydrates of carbon. It does not mean the same thing as “sugar”. Sugar is more of an everyday term for sucrose and other sweet-tasting simple carbohydrates. The simple truth is that all sugars are carbohydrates, but not all carbohydrates are sugars.
Carbohydrates are organic compounds that are widespread in nature. In the human diet, they come mainly from plants, with smaller amounts from animal foods and mushrooms. They are readily available, relatively inexpensive and provide plenty of energy. Carbohydrates account for more than half of the calories the human body needs to function, while the brain’s energy needs are met almost entirely by blood sugar, or glucose.
Dietary carbohydrates, also known as saccharides, are divided into monosaccharides, oligosaccharides and polysaccharides. The most important oligosaccharides are disaccharides. The monosaccharides most often discussed are glucose, also known as grape sugar, and fructose, or fruit sugar. These are abundant in honey, fruit and juices. Galactose is best known for combining with glucose to form lactose, or milk sugar.
Glucose is by no means the sweetest sugar, as is sometimes assumed. It ranks only third in sweetness, after fructose and sucrose. Blood sugar refers to the amount of glucose in the blood. Glucose is also a building block of sucrose, maltose and lactose, and is the monomer of starch, glycogen and cellulose. Glucose is absorbed very rapidly from the human digestive tract. Fructose is absorbed more slowly but is the sweetest sugar.
What types of plant carbohydrates are found in food?
Important disaccharides include sucrose, lactose and maltose. Sucrose is ordinary table sugar and is abundant in sugar cane and sugar beet. Lactose is milk sugar. Cow’s milk contains approximately 5% lactose, which provides 30…50% of its energy content. Breast milk has a higher lactose content, reaching 7%. Maltose, or malt sugar, is a plant sugar formed when starch is broken down (hydrolyzed) during seed germination.
Starch is the most familiar dietary polysaccharide. When you eat starchy foods, digestion ultimately breaks the starch down into glucose. Potato tubers and cereal grains contain large amounts of starch. Eating liver, meat or mushrooms also provides some glycogen. Because its structure resembles that of starch, glycogen is sometimes called animal starch.
Food also contains polysaccharides that are not made up of glucose residues. One example is inulin, which consists of fructose residues. Sources of inulin include Jerusalem artichokes, black salsify and chicory. Dietary fiber, including hemicelluloses, pectic substances, cellulose and other similar compounds, can also be loosely counted among dietary polysaccharides. These are more than just “bulk”. They affect feelings of fullness and digestion.
A little useful history
Humans began including such large amounts of carbohydrates in their diet relatively recently. Large-scale, deliberate cereal cultivation began 18,000 years ago in East Asia, 12,000 years ago in Egypt, 4000 years ago in the Mediterranean region and 2500 years ago in Northern Europe. Two tentative conclusions can be drawn from this. First, adaptation to a carbohydrate-rich diet is a fairly recent development in modern human evolution. Second, different populations have adapted differently to carbohydrate consumption.
A classic example is intolerance to lactose, or milk sugar. Descendants of peoples with a history of livestock farming are more likely to retain the activity of lactase, the enzyme needed to break down lactose, throughout their lives. Lactose intolerance is more common among populations that began consuming milk relatively recently, such as American Indians in Alaska, Greenlandic Inuit and the Japanese. When lactose is not broken down, intestinal bacteria convert it into lactic acid and other organic acids. This can interfere with water absorption, trigger intestinal contractions and cause diarrhea.
A similar line of reasoning has been applied to plant carbohydrate consumption. The hypothesis is that sustained excessive carbohydrate intake may be more harmful to people in Northern Europe than to those in East Asia, because Asian populations had more time to adapt to a carbohydrate-rich diet. This does not mean you should fear potatoes or bread. Rather, it suggests that excesses, particularly excessive sucrose consumption, are worth avoiding.
Sugar production and consumption began in India around 3000 BCE. Europeans first encountered sugar during Alexander the Great’s expedition to India in 327 BCE. It made a powerful first impression: a reed grew in India that produced honey without bees. In China, sugar was initially called stone honey; in Egypt, Indian salt. Europe’s first cane sugar refinery was not established until either the VIII or IX century, when it was set up by Arabs. Sugar production began in London in 1544 and in Russia in 1718.
In 1747, German chemist Andreas Margraff made an important discovery: the sugar found in several varieties of beet could be extracted through crystallization. Beets at the time contained just 1.3% sugar, but the idea had great potential. Margraff’s student F. K. Achard continued the experiments and breeding work. In 1802, the first factory producing beet sugar began operating in Silesia. Today, sugar beet accounts for slightly more than a third of global sugar production.
What do carbohydrates do in your body?
The best-known role of carbohydrates is to provide energy. The complete breakdown of 1 g of glucose in the human body releases approximately 4 kcal of energy. According to the original account, carbohydrates should ideally provide 56…60% of the body’s total energy intake. This is not an invitation to eat unlimited sweets, but an indication that carbohydrates are an important fuel in an everyday diet.
Carbohydrates also serve as an energy reserve. Glycogen stored in the liver and muscles provides a temporary reserve of glucose. Many of the body’s cells can use the glucose released when liver glycogen is broken down by hydrolysis. Glucose released from muscle glycogen, however, is reserved for the muscles themselves. This is why replenishing glycogen stores is often discussed after a hard workout.
Carbohydrates also have a protective role, as they form part of antibodies, mucopolysaccharides and blood clotting factors. Their structural role takes several forms: monosaccharides are the building blocks of polysaccharides, glycoproteins and glycolipids form part of biological membranes, and polysaccharides are components of connective tissue, bones and cartilage. Ribose and deoxyribose are also needed for nucleic acid synthesis.
So what actually happens when you consume too many carbohydrates? The problem is not a single potato or a bowl of porridge. It arises when sugary drinks, sweets and refined flour products consistently provide a large share of your daily energy. Your diet can then quickly drift toward meals that fill you up only briefly yet supply plenty of energy.
Practical portions: plant carbohydrates on your plate
There is no question that you need carbohydrates as a source of glucose every day. The question is how much. It is difficult to specify an exact amount because, when needed, the body can synthesize some glucose from certain amino acids and intermediates of lipid metabolism. Your carbohydrate requirements also depend on your overall energy balance.
The original calculation suggests that 320…350 g of carbohydrates per day would be suitable for many people. If 1 g of carbohydrates provides around 4.1 kcal of energy, this would yield a total of 1300…1450 kcal. If your daily food intake provides 1450 kcal and carbohydrates are meant to account for 60%, they would need to supply ~900 kcal, equivalent to approximately 220 g of saccharides. If your food provides 3000 kcal, the corresponding amount would be around 450 g of carbohydrates.
Note: these figures refer to the amount that is fully absorbed. Food always contains cellulose and other carbohydrates that the human body cannot absorb, so the amount actually eaten may be greater. This is where the distinction between eating refined sugar and eating whole grains, legumes and vegetables matters. Both can provide carbohydrates, but their effects on fullness and the quality of your diet are not the same.
The recommended dietary fiber intake would be 15…35 g per day. Some authors suggest smaller amounts, such as 15…20 g, while some sources recommend a higher intake, such as 20…35 g. Consistently consuming too much dietary fiber can also be harmful, as it can bind several minerals the body needs into poorly soluble compounds. In practice, however, the opposite is more common: dietary fiber intake is two to three times lower than recommended.
The original text drew a clear line for sweet monosaccharides and disaccharides: an intake providing no more than 6…9% of total energy is considered normal. The remaining energy requirement allocated to carbohydrates, or 48…50%, is met mainly by polysaccharides—essentially starch. Today, the typical pattern is often different: sucrose alone meets 20…25% of the body’s total energy needs.
Consistently consuming too much sugar can contribute to obesity. A simple rule applies: if you regularly get more than 60% of your calories from carbohydrates, with a large share coming from sweet foods and drinks, controlling your body weight becomes harder. Diet is not the only cause of type 2 diabetes, as genetic predisposition also plays an important role. However, if that predisposition is present, excessive sugar intake becomes more dangerous. During the Second World War and the years immediately afterward, type 2 diabetes was relatively rare in the population. Dietary changes—food shortages and the lack of refined foods—were considered one reason for this.
Another risk is elevated blood lipid levels and an increased risk of cardiovascular disease. This effect may occur particularly when carbohydrate intake is consistently excessive and fat intake is too low: carbohydrates regularly provide significantly more than 60% of calories, while fats provide less than 25%. Excessive sugar intake is also linked to tooth decay, as bacteria in dental plaque convert sugars into organic acids within minutes.
FAQ: plant carbohydrates and everyday eating
Are plant carbohydrates better than sugar?
Usually, yes, if we are talking about foods rich in starch and dietary fiber, rather than just refined sugar derived from plants. Potatoes, grains, vegetables and legumes provide bulk and often dietary fiber as well as energy. Table sugar provides energy, but almost nothing else.
Do you need to avoid carbohydrates when trying to lose weight?
No. The amount and source matter more than the label “plant carbohydrate”. If you keep your energy intake under control, porridge, potatoes, rye bread, fruit and vegetables can all fit well into your diet during weight loss. Cutting back on sugary drinks and sweets is an easier place to start.
Why does dietary fiber matter when it comes to carbohydrates?
Dietary fiber adds bulk to food and supports digestion. It does not provide energy in the same way as glucose or sucrose, but it affects how full you feel after a meal. That is why it is worth choosing whole grains, vegetables and other foods rich in dietary fiber more often.
Author: Marek Morozov
Source: WHO – healthy eating.
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