It is widely recognized that the overconsumption of simple sugars like glucose, fructose and sucrose is unhealthy and often deadly1,2. In addition, low-carbohydrate diets are often more successful and healthier than low-fat diets3-5.
However, it is an oversimplification to say that all carbohydrates are the same. Some dietary carbohydrates have important health benefits, including helping the immune system6. The main factor that determines whether a carbohydrate is healthy or unhealthy is its glycemic index or the effect it has on one’s blood glucose levels6. That is, simple sugars cause a rapid increase in blood glucose levels, which is quite dangerous. In contrast, complex carbohydrates cause a much slower and gradual increase in blood glucose, meaning that they have a lower glycemic index than simple sugars6.
Overconsumption of simple carbohydrates and foods with a high glycemic index can lead to hyperglycemia, smoldering inflammation, metabolic syndrome, an increase in abdominal fat and type-2 diabetes, as well as improperly regulated immune responses6-8. When over consumed, glucose and its metabolites can react with proteins and body tissues6. The products of these reactions are advanced glycation end products (AGEs) as well as reactive oxygen species that are quite toxic. One important example is glycated hemoglobin, usually known as HbA1c, the concentration of which is elevated in diabetes6.
Moreover, some complex carbohydrates have specific effects. Two of the best-known examples are glucosamine and chondroitin sulfate6,9. Chondroitin sulfate is a major component of the extracellular matrix and a popular dietary supplement. It protects chondrocytes, which are the cells in healthy cartilage that produce and maintain the cartilaginous matrix9. It was also more effective than placebo in reducing pain, joint swelling and effusion while improving articulate function and in preventing the joint space in the knee from narrowing in patients with osteoarthritis7. Glucosamine may also be a useful addition to cyclosporine A in treating psoriasis, due to its immunomodulatory effects10. There are also many immunomodulatory water-soluble polysaccharides and polysaccharide-protein complexes in traditional medicines, edible mushrooms, many types of seaweed, oats, soybeans, ginseng, turmeric, licorice and several fruits6. They enhance and/or activate immune responses in macrophages and the complement system6,11. They increase the ability of our endogenous macrophages to kill cancer cells and microorganisms. Water-soluble polysaccharides also increase the secretion of cytokines and chemokines that have anti-tumor activity, wound-healing and other therapeutic effects6,11.
For example, polysaccharides isolated from blue-green algae, Spirulina platensis, have anti-tumor and anti-metastatic activities6,11. Many other polysaccharides from several sources have anti-cancer activities as well12. Dietary polysaccharides also have healthy effects on the gut microbiome, which can improve one’s nutrition, immune response, resistance to pathogens, intestinal epithelial development and energy metabolism12. They may also improve communication between the gut microbiome and one’s brain13. That is, the gut microbiome and brain communicate with each other through endocrine, immune, neural and metabolic pathways. So, improvements in the gut microbiome can improve cognitive function6,13.
In addition, at least 131 drugs based on carbohydrates are listed in the United States, European, Japanese and Chinese Pharmacopoeias and 18 are marketed6,14. At the same time, a protein-polysaccharide complex (PSK, Krestin), from the mushroom Coriolus versicolor is quite popular in Japan6,14. A different peptide-polysaccharide from C. versicolor is popular in China due to its anti-cancer and immunomodulatory properties. These and several other polysaccharide-protein complexes have anticancer activities6,15. Mushrooms are popular folk medicines that have attracted considerable attention because of their efficient antitumor activities16.
Mother’s breast milk also contains a class of carbohydrates called human milk oligosaccharides (HMOs) that encourage the growth of beneficial bacteria, such as Bifidobacterium infantis in the baby’s gastrointestinal tract17. This protects the baby from being colonized by pathogenic bacteria. So, HMOs help prevent neonatal diarrhea and respiratory tract infections17. The mother’s breast milk contains oligosaccharides that stimulate the growth of beneficial communities of Bacteria, including Bifidobacterium species. This leads to better cognitive development of the baby. In contrast, prenatal stress can cause dysbiosis in the baby’s gut microbiome.
Moreover, children with neurodevelopment disorders, such as autism spectrum disorder often have an unbalanced gut microbiome that can lead to atypical patterns of connectivity between the cells in the brain. HMOs are especially important in ensuring proper development of the baby’s microbiome17. Not just the HMOs, but also healthy bacteria in mother’s the milk (the milk glycobiome) influence microbiota development and the overall health of the gut18. They protect against infectious diseases and act as prebiotics, selecting for the growth of beneficial intestinal bacteria. The prebiotic effect helps to prevent diseases such as necrotizing enterocolitis, a common and devastating disease of preterm infants. The neonatal intestinal mucosa, luminal nutrients and microbiota ensure proper homeostasis in the developing gut. So, establishing a health-promoting gut microbiome early in life is crucial18.
There is a class of carbohydrates called fatty acid glycosides that is not soluble in water. They were identified in the Polynesian fruit called noni (Morinda citrifolia). They are beneficial to the immune system19,20. They also have antibacterial, anticancer, analgesic (pain killing), anti-inflammatory and cancer chemopreventive properties21,22.
In conclusion, the simple carbohydrates (fructose, sucrose and glucose) are unhealthy when over consumed. They cause a rapid increase in blood glucose. In contrast, complex carbohydrates can be quite healthy when consumed in moderation. Water-soluble polysaccharides, HMOs in mother’s milk and fatty acid glucosides are also healthy.
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4 Shih C.W. et al., Changes in blood lipid concentrations associated with changes in intake of dietary saturated fat in the context of low-carbohydrate weight-loss diet: a secondary analysis of the Diet Intervention Examining the Factors Interacting with Treatment Success (DIETFITS) trial, in American Journal of Clinical Nutrition, Volume 109, pages 433-441, 2019.
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