This article was written by Registered Dietitian Maeve Hanan and Student Dietitian and Dietetically Speaking Intern Sophie Gastman.
Carbohydrates have notoriously gained a bad rep in the media over the years, but do they actually live up to this reputation? The short answer is no. The truth is, carbohydrates are really important for our health and are the body’s preferred type of energy for fueling our brain, muscles and organs.
This article explains the science behind why we need carbohydrates to function optimally in our daily lives and the consequences of not consuming enough of this nutrient.
What Are Carbohydrates?
Carbohydrates are one of the three macronutrients found in our diets (the other two being protein and fat). Macronutrients are nutrients that we need to consume in relatively large amounts, whereas micronutrients (like vitamins and minerals) are those that we need in relatively small amounts.
Carbohydrates are present in food in three different forms – sugar, starch and fibre. During digestion, simple sugars and complex carbohydrates (except for fibre) are broken down into a sugar called glucose which the body uses as it’s main source of energy.
Sources of starchy carbohydrates include food like: bread, potatoes, pasta, rice and grains. Whereas the carbohydrates in foods like sweets, sugary drinks and jam come from simple sugars. We also find some naturally occurring simple sugars in fruit, vegetables and dairy. Fibre is found in the parts of plants that we can’t fully digest. Good sources of fibre include fruit, vegetables, nuts, seeds, legumes and wholegrains.
Why Do We Need Carbohydrates?
The main purpose for consuming carbohydrates is to provide us with energy.
When we consume carbohydrates, they are digested and absorbed into the small intestine and then supply glucose to the blood. This glucose is either used in tissues for fuel, or is stored as glycogen in the liver and muscles. Excess glucose is converted to fatty acids and stored as body fat for long-term storage of energy.
Certain types of carbohydrate-containing foods, particularly whole grains, oats, fruit and vegetables, also provide a variety of vitamins and minerals; depending on the food in question. One of these nutrients found in wholegrains is B-vitamins which are vital for a whole host of metabolic processes and need to be consumed regularly in the diet as they are not stored in the body.
Fibre is an important component of our diets as it’s responsible for keeping the digestive system healthy and reducing the risk of constipation.
Research has shown that a diet high in fibre, especially whole grains, can be protective against type 2 diabetes, play a role in preventing breast cancer, and reduce risk of coronary heart disease (CHD) (1-3).
Consumption of carbohydrates has also been linked to improving your mood by increasing the availability of an amino acid called tryptophan in the brain. This amino acid is used to synthesise serotonin (A.K.A. the happy hormone), so the more tryptophan you have available, the more serotonin is synthesised (4). However, it is important to note that the scientific evidence surrounding influencing tryptophan levels through diet alone is lacking (4). On the other hand, carbohydrates may play a role in reducing levels of the stress hormone cortisol and have been shown to improve complex task performance when performing under stress (5-6).
It’s also important to consider that carbohydrates are the main staple of many traditional cultural dishes and most people find carbohydrate-containing foods to be tasty, comforting and satisfying. Remember, enjoying food is of equal importance to obtaining all of the nutritional benefits it brings, even though sometimes these are not mutually exclusive.
How Much Carbohydrate Do We Need?
Carbohydrate requirements differ based on various factors such as age, activity level and medical factors. Numerous studies have shown that the brain alone requires 110 – 145g of carbohydrate per day, in the form of glucose (7). This is the carbohydrate equivalent of roughly 6 thick slices of bread per day to function optimally (i.e. a minimum of a portion of starchy carbohydrates at each meal) – and this is before we add in the carbohydrate our body needs for movement.
According to the UK government’s Eatwell Guide, over ⅓ of the food we eat should be made up of starchy food and over another ⅓ should come from fruits and vegetables. This means that over half of our daily intake should come from starchy carbohydrates and fruits and vegetables.
What Happens if We Don’t Eat Enough Carbohydrate?
Not supplying our body with enough carbohydrates means that the body will start to use less efficient sources of fuel.
For example, either by breaking down muscle to use the protein for energy or converting fats to ‘ketone bodies’. This process is commonly known as ketosis, and whilst it is praised by supporters of the keto diet, it can have a whole host of negative side-effects including headaches, muscle cramps, difficulty focusing, constipation, and loss of energy (8). It’s important to remember that this is the body’s ‘back-up’ option to protect itself from starvation, not a weight-loss method.
There are some medical uses for low-carbohydrate diets and the ketogenic diet. For example, the ketogenic diet is sometimes used in the treatment of certain types of childhood epilepsy. But this should only be done under close medical and dietetic supervision. See here for more information about the keto diet.
Low-carbohydrate diets are also commonly lower in fibre, which as mentioned above, is essential for good bowel and heart health. Having a low fibre intake is also very likely to increase the risk of constipation – a very unpleasant side effect!
Not eating enough carbohydrate-containing foods could also lead to under-fuelling by not consuming enough energy overall. If ongoing, this can lead to a reduction in metabolism and body systems functioning less efficiently. Female hormones are particularly sensitive to calorie and carbohydrate intake, so underfuelling in terms of carbohydrate intake can contribute to hormonal disruptions (watch this space for an article on this topic soon).
But What About Sugar?
Sugar also gets very bad press, however, simply categorising foods into ‘good or bad’ is never helpful. There’s no denying that too much sugar isn’t great for our health (particularly our dental health), but completely avoiding sugar is an unhealthy and restrictive approach, especially as it’s found naturally in many types of foods, including fruit and vegetables.
Sugar can also be really useful for aiding athletic performance, particularly endurance activities (9).
It is also very natural to have a sweet tooth, so this isn’t something to be ashamed of.
This is likely to have developed as an evolutionary survival mechanism to encourage consumption of carbohydrates considering what an important fuel source this is for humans, and consuming sweet foods triggers a pleasurable response in our brain (10). Check out this article for more information about sugar.
Take Home Message
Carbohydrates are in desperate need of rebranding to show-off how essential they are to our daily lives. They are not something to be feared, rather something that needs to be cherished for all of the positive effects they have on our energy levels, brain health, digestive health and our taste buds!
- Meyer, K., Kushi, L., Jacobs, D., Slavin, J., Sellers, T. and Folsom, A., 2000. Carbohydrates, dietary fiber, and incident type 2 diabetes in older women. The American Journal of Clinical Nutrition, 71(4), pp.921-930.
- Park, Y., Brinton, L., Subar, A., Hollenbeck, A. and Schatzkin, A., 2009. Dietary fiber intake and risk of breast cancer in postmenopausal women: the National Institutes of Health–AARP Diet and Health Study. The American Journal of Clinical Nutrition, 90(3), pp.664-671.
- Streppel, M., Ocké, M., Boshuizen, H., Kok, F. and Kromhout, D., 2008. Dietary fiber intake in relation to coronary heart disease and all-cause mortality over 40 y: the Zutphen Study. The American Journal of Clinical Nutrition, 88(4), pp.1119-1125.
- Soh, N. and Walter, G., 2011. Tryptophan and depression: can diet alone be the answer?. Acta Neuropsychiatrica, 23(1), pp.3-11.
- Markus, C., 2007. Effects of carbohydrates on brain tryptophan availability and stress performance. Biological Psychology, 76(1-2), pp.83-90.
- Soltani et al. 2019. Increasing Dietary Carbohydrate as Part of a Healthy Whole Food Diet Intervention Dampens Eight Week Changes in Salivary Cortisol and Cortisol Responsiveness. Nutrients. 2019 Nov; 11(11): 2563.
- Owen, O., Morgan, A., Kemp, H., Sullivan, J., Herrera, M. and Cahill, G., 1967. Brain Metabolism during Fasting*. Journal of Clinical Investigation, 46(10), pp.1589-1595.
- Kirkpatrick, C., Bolick, J., Kris-Etherton, P., Sikand, G., Aspry, K., Soffer, D., Willard, K. and Maki, K., 2019. Review of current evidence and clinical recommendations on the effects of low-carbohydrate and very-low-carbohydrate (including ketogenic) diets for the management of body weight and other cardiometabolic risk factors: A scientific statement from the National Lipid Association Nutrition and Lifestyle Task Force. Journal of Clinical Lipidology, 13(5), pp.689-711.e1.
- Wallis, G. and Wittekind, A., 2013. Is There a Specific Role for Sucrose in Sports and Exercise Performance?. International Journal of Sport Nutrition and Exercise Metabolism, 23(6), pp.571-583.
Drewnowski et al. 2012. Sweetness and Food Preference. J Nutr. 142(6): 1142S–1148S [Accessed February 2021 via: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3738223/]