Carbohydrates

Carbohydrates are – beside fats and protein – part of the so-called macro nutrients. As macro nutrients we understand nutrients, which can be utilised by our bodies as an energy and carbon source.

At a metabolic energy density of 17 kJ/g (4 kcal/g) carbohydrates are relatively inefficient energy carriers. We can ferment carbohydrates (use for energy without the use of oxygen) – something we can't do with fats. Carbohydrate fermentation is both a bane and benefit, something we'll go over in a future piece on cancer and mitochondria.

In our food, we primarily find carbohydrates in fruits, berries, roots, tubers, and grains. These carbohydrates are almost always available as single molecules of two or more sugars (di-, oligo-, and polysaccharides). The chemical understanding of the term 'carbohydrate' also includes what is considered to be fibre in the nutritional understanding. Keep that in mind when reading up upon these. Carbohydrates of the nutritional understanding are just those carbohydrates of the chemical understanding, which we can digest and use for energy, whereas fibre is indigestible.

An important consideration, which differentiates carbohydrates from fats and protein, is, that no essential carbohydrates exist. This means, that we can synthesise all the carbohydrates (or sugar) we need ourselves. This is in fact one of the main functions of our liver and keeps our blood sugar nice and level (Zhang et al. 2018). Body internally, sugar is essential for our survival, because our red blood cells – alone amongst all our cells – can only gain energy by fermentation (Chatzinikolaou et al. 2024). As red blood cells have lost the ability to use oxygen to burn fuel, they need sugar.

Our bodies as holistic organisms, however, don't need to consume any sugar or carbohydrates with our diet. Sugar and carbohydrate consumption can in fact derail our body and lead to such ailments as insulin resistance and Type 2 Diabetes (Adochio et al. 2009, Giebelstein et al. 2012, Istfan et al. 2021, Kim et al. 2008).

As a survival food, carbohydrates are somewhat useful. As a health food, however, carbohydrates are the opposite. In moderation – especially when doing large amounts of exercise –, they probably aren't fatal, but they probably shouldn't be used as our bodies' main energy source.

Adochio, R.L., Leitner, J.W., Gray, K., Draznin, B., and Cornier, M.-A. (2009). Early responses of insulin signaling to high-carbohydrate and high-fat overfeeding. Nutrition & Metabolism 6, 37. 10.1186/1743-7075-6-37.

Chatzinikolaou, P.N., Margaritelis, N.V., Paschalis, V., Theodorou, A.A., Vrabas, I.S., Kyparos, A., D'Alessandro, A., and Nikolaidis, M.G. (2024). Erythrocyte metabolism. Acta Physiologica 240, e14081. 10.1111/apha.14081.

Giebelstein, J., Poschmann, G., Højlund, K., Schechinger, W., Dietrich, J.W., Levin, K., Beck-Nielsen, H., Podwojski, K., Stühler, K., Meyer, H.E., and Klein, H.H. (2012). The proteomic signature of insulin-resistant human skeletal muscle reveals increased glycolytic and decreased mitochondrial enzymes. Diabetologia 55, 1114-1127. 10.1007/s00125-012-2456-x.

Istfan, N., Hasson, B., Apovian, C., Meshulam, T., Yu, L., Anderson, W., and Corkey, B.E. (2021). Acute carbohydrate overfeeding: a redox model of insulin action and its impact on metabolic dysfunction in humans. Am J Physiol Endocrinol Metab 321, E636-e651. 10.1152/ajpendo.00094.2021.

Kim, J.A., Wei, Y., and Sowers, J.R. (2008). Role of mitochondrial dysfunction in insulin resistance. Circ Res 102, 401-414. 10.1161/circresaha.107.165472.

Zhang, X., Yang, S., Chen, J., and Su, Z. (2018). Unraveling the Regulation of Hepatic Gluconeogenesis. Front Endocrinol (Lausanne) 9, 802. 10.3389/fendo.2018.00802.