Carbohydrates have a reputation problem. This is no fault of their own but is due to widespread misunderstanding about what carbohydrates are. For instance it is commonly (and mistakenly) believed that carbohydrates are detrimental to human health; that the low-carb diet is the one to turn to for weight loss; that somehow the human body actually evolved to prefer to run on fats and protein. It’s time to sort through the chaos.
First of all, what are carbohydrates?
Carbohydrates, along with fat and protein, are the three macronutrients that make up the human diet. Carbohydrates at their most basic level are made up of carbon, hydrogen and oxygen atoms and their main purpose is to provide energy for body processes. Glucose is the primary source of energy for every cell in the body and in fact body organs such as the brain and red blood cells depend entirely on glucose for energy. They are unable to utilize fat or protein for this purpose (except in states of severe carbohydrate deprivation when they can use alternate fuels for survival), explaining why our bodies strive to maintain a steady and optimum level of glucose in the bloodstream. (1) Carbohydrates that are not immediately used for energy can be stored in the liver and muscles as glycogen (a polysaccharide carbohydrate similar to starch) or turned into fat and stored for later energy needs.
Categories of carbohydrates:
Sugars: Sweet short-chain carbohydrates such as the monosaccharides (single unit sugars) glucose, fructose and galactose and the disaccharides (double unit sugars) sucrose and lactose. They are quickly and easily absorbed by the body
Starches: Long chains of sugar molecules known as polysaccharides that are linked together such that the body is required to break the bonds between the molecules to absorb the sugars.
Fiber: Rigid and strong polysaccharides that cannot be digested by humans. However the bacteria that make up the microbiota of the human digestive tract thrive on fiber. Fiber does not provide energy directly but the short-chain fatty acids produced by friendly gut bacteria can be used for energy by some cells such as the epithelial cells that line our intestines.
Sugar alcohols (polyols): These carbohydrates do not occur naturally but can be produced commercially during the transformation of sugars. They are sweet in taste but provide little energy. Examples are sorbitol and xylitol.
Clearing up the carbohydrate misunderstanding
Carbohydrates exist on the earth in a multitude of forms and, when it comes to health, not all carbohydrates are alike. In fact there is a huge difference between whole (complex) carbohydrates versus refined (simple) carbohydrates. Understanding this fact is crucial to comprehending the role of carbohydrates in a healthy diet.
Whole carbohydrates are healthy foods. They have not been processed and so they contain their natural fiber and nutrients. Examples are vegetables, legumes, fruits and whole grains. Whole carbohydrate consumption is linked to excellent health and low risk of disease (2,3,4,5,6).
Refined carbohydrates have been processed which removes their natural fiber and many of their nutrients. Examples are white bread, white pasta, white rice, sweet baked goods, sugar-sweetened beverages and fruit juices. Refined carbohydrate consumption is linked to chronic diseases such as type-2 diabetes, cardiovascular disease, high cholesterol, high blood pressure and obesity (7,8,9,10,11,12,13).
A 2016 study was devised specifically to ascertain the optimal macronutrient composition of a healthy diet. In other words, what proportions of protein, carbohydrate and fat should be eaten daily for superlative human health. Participants included 1785 people with type-2 diabetes. Their dietary habits were assessed along with measurements of body composition, BMI, blood lipids, hemoglobin-A1c (HbA1c – a measurement of blood sugar levels over the previous 3 months) and C-reactive protein (CRP – a measurement of inflammation). Results showed that increasing fat intake from 25% to 35% of energy intake is associated with a significant increase in LDL-cholesterol, triglycerides, HbA1c and CRP, all indicators of declining health. Intake of added sugar greater than 10% of energy is associated with detrimentally elevated blood lipid levels and high CRP (increased inflammation). On the other hand, fiber intake of more than 15 gm per 1000 calories is associated with improved blood lipid levels, lower HbA1c (better control of diabetes) and lower CRP (less inflammation). These results support the reduction of fat and added sugar and the increase of whole carbohydrates in a diet created for excellent health (14).
There is good reason to worry about inflammation in the body. It has been linked to early onset and development of the chronic diseases that trouble many people as they age including cardiovascular disease, diabetes, cancer and neurodegenerative diseases. Inflammation is a natural result of the act of eating itself, stemming from the increase in blood sugar and lipids immediately after a meal that in turn boost the formation of inflammation-producing reactive oxygen species. Added sugars and other refined carbohydrates intensify this inflammation; whole carbohydrates high in fiber and antioxidants diminish it (15,16,17). An after-meal walk can also improve inflammation partly by lowering blood glucose levels (18,19).
If you’re worried about weight loss, investigations such as the following can set your mind at ease. The on-going National Weight Control Registry is a long-term study of success in weight-loss. It has found that the majority of people who lose weight successfully and keep the pounds off over long time periods eat a low-energy low-fat diet based on whole or minimally processed plant foods like vegetables, fruits and whole grains (20). Additionally a review of 140 studies on carbohydrate intake and body mass index (BMI) found no connection between glycemic index (a measurement of how fast sugar is released from a food) and BMI. There was a link found however between diets high in whole carbohydrates and lower BMI (21).
Our daily lives are hectic with many meals prepared and eaten in a rush. When you’re short on time and long on hunger it is difficult to make the best food choices for good health. But the carbohydrate situation is really very simple and can be summed up by remembering only two guidelines:
1. Eat real food as it comes from the earth. For instance choose brown rice over white and whole fruit over fruit juice.
2. Avoid processed foods. This means that when you read the nutrition label on a food package look for listed ingredients that are simple whole foods, not chemicals or added sugars, fats and salt.
The following are attributes of “good carbs”;
High in multiple nutrients such as vitamins, minerals and antioxidants
Rich in fiber
Low in calories
Low in sodium
Low in saturated fat
Contain no cholesterol or trans-fats
Contain no added oils
Contain no refined grains such as white flour
Contain no added sugars such as glucose-fructose, corn syrup, honey, fruit juice or the many other ingredients with names designed to hide the fact that they are really just a form of sugar
It is well-documented that a nutritious diet, one that supports a long life spent in good health, is a diet abundant in whole carbohydrates such as vegetables, legumes, fruits, whole grains, nuts and seeds and lacking in refined carbohydrates (2,3,4,5,6,14). It is apparent that not all carbohydrates are created equal. Perhaps this article will help clear away some of the confusion and make your food choices easier.
2 Dauchet, L., Amouyel, P., Hercberg, S., Dallongeville, J. Fruit and Vegetable Consumption and Risk of Coronary Heart Disease: A Meta-Analysis of Cohort Studies . J Nutr. Oct 2006; 136(10): 2588–2593.
3 Ford, E.S., Mokdad, A.H. Fruit and Vegetable Consumption and Diabetes Mellitus Incidence among U.S. Adults. Preventive Medicine Jan 2001; 32(1): 33-39.
Volume 32, Issue 1, January 2001, Pages 33-39
4 Afshin, A., Micha, R., Khatibzadeh, S., Mozaffarian, D. Consumption of nuts and legumes and risk of incident ischemic heart disease, stroke, and diabetes: a systematic review and meta-analysis. Am J Clin Nutr. 2014 Jul; 100(1): 278-288.
5 Wu, H., Flint, A.J., Qi, Q., van Dam, R.M., Sampson, L.A., Rimm, E.B., Holmes, M.D., Willett, W.C., Hu, F.B., Sun, Q. Association between dietary whole grain intake and risk of mortality: two large prospective studies in US men and women. JAMA Intern Med. 2015 Mar; 175(3):373-384.
6 Aun, D., Norat, T., Romundstad, P., Vatten, L.J. Whole grain and refined grain consumption and the risk of type 2 diabetes: a systematic review and dose-response meta-analysis of cohort studies. Eur J Epidemiol. 2013 Nov; 28(11): 845-858.
7 Yu, D., Shu, X.O., Li, H., Xiang, Y.B., Yang, G., Gao, Y.T., Zheng, W., Zhang, X. Dietary carbohydrates, refined grains, glycemic load, and risk of coronary heart disease in Chinese adults. Am J Epidemiol. 2013 Nov 15; 178(10):1542-1549.
8 Greenwood, D.C., Threapleton, D.E., Evans, C.E.L., Cleghorn, D.L., Nykjaer, C., Woodhead, C., Burley, V.J. Glycemic Index, Glycemic Load, Carbohydrates, and Type 2 Diabetes: Systematic review and dose–response meta-analysis of prospective studies. Diabetes Care. 2013 Dec; 36(12): 4166–4171.
9 Zuñiga, Y.L., Rebello, S.A., Oi, P.L., Zheng, H., Lee, J., Tai, E.S., Van Dam, R.M. Rice and noodle consumption is associated with insulin resistance and hyperglycaemia in an Asian population. Br J Nutr. 2014 Mar 28; 111(6):1118-1128..
10 Te Morenga, L.A., Howatson, A.J., Jones, R.M., Mann, J. Dietary sugars and cardiometabolic risk: systematic review and meta-analyses of randomized controlled trials of the effects on blood pressure and lipids. Am J Clin Nutr. 2014 Jul; 100(1):65-79.
11 Bray, G.A. Energy and fructose from beverages sweetened with sugar or high-fructose corn syrup pose a health risk for some people. Adv Nutr. 2013 Mar 1; 4(2):220-225.
12 Schulze, M.B., Manson, J.E., Ludwig, D.S., Colditz, G.A., Stampfer, M.J., Willett, W.C., Hu, F.B. Sugar-sweetened beverages, weight gain, and incidence of type 2 diabetes in young and middle-aged women.
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13 Yang, Q., Zhang, Z., Gregg, E.W., Flanders, W.D., Merritt, R., Hu, F.B. Added sugar intake and cardiovascular diseases mortality among US adults. JAMA Intern Med. 2014 Apr; 174(4):516-524.
14 Vitale, M., Masulli, M., Rivellese, A.A., Babini, A.C., Boemi, M., Bonora, E., Buzzetti, R., Ciano, O., Cignarelli, M., Cigolini, M., Clemente, G., Citro, G., Corsi, L., Dall’Aglio, E., Del Pratoshow, S. et al. Influence of dietary fat and carbohydrates proportions on plasma lipids, glucose control and low-grade inflammation in patients with type 2 diabetes—The TOSCA.IT Study. Eur J NutrJune 2016; 55(4): 1645-1651.
15 Watzl, B. Anti-inflammatory Effects of Plant-Based Foods and of their Constituents. Int J Vitamin & Nutr Research (2008); 78: 293-298
16 Ludwig, D.S., Hu, F.B., Tappy, L, Brand-Miller, J. Analysis – Science and Politics of Nutrition – Dietary carbohydrates: role of quality and quantity in chronic disease. BMJ June 2018; 361:k2340.
17 O’Keefe, J.H., Gheewala, N.M., O’Keefe, J.O. Dietary Strategies for Improving Post-Prandial Glucose, Lipids, Inflammation, and Cardiovascular Health. J Amer Coll Cardio Jan 2008; 51(3):
18 DiPietro, L., Gribok, A., Stevens, M.S., Hamm, L.F., Rumpler, W. Three 15-min Bouts of Moderate Postmeal Walking Significantly Improves 24-h Glycemic Control in Older People at Risk for Impaired Glucose Tolerance. Diabetes Care 2013 Jun; DC_130084.
19 Dimitrova, S., Hultenga, E., Honga, S. Inflammation and exercise: Inhibition of monocytic intracellular TNF production by acute exercise via β2-adrenergic activation. Brain, Behavior, and Immunity March 2017; 61: 60-68.
20 Shick, S.M., Wing, R.R., Klem, M.L., McGuire, M.T., Hill, J.O., Seagle, H. Persons successful at long-term weight loss and maintenance continue to consume a low-energy, low-fat diet. J Am Diet Assoc. 1998 Apr; 98(4): 408-413.
21 Gaesser, G.A. Carbohydrate Quantity and Quality in Relation to Body Mass Index. J Acad Nutr & Dietetics Oct 2007: 107(10): 1768-1780.