Why are high carb diets still promoted for everyone?

By Cliff Harvey

Dietary guidelines for health are still heavily weighted (excuse the pun!) in favour of high-carbohydrate diets. 

Nutrient Reference Values (NRV) for New Zealand and Australia for example state that the diet should contain a minimum of 45% of its calories from carbohydrate (1) and New Zealand Heart Foundation position statements on carbohydrate (currently being updated) suggest a range of 55%-65% caloric intake should be obtained from carbohydrate along with reducing intake of total and saturated fat (2). 

Why is this the case? 

The World Health Organisation (WHO) published dietary guidelines in 1998 (3) suggesting a range of 55%-70% of calories come from carbohydrate, with a 2007 update suggesting that there is little evidence for the lower threshold and suggesting this could be lowered to 50% of calories (4). 

All of these institutional recommendations would be considered, according to the definitions provided by Wheeler et al. as being moderate to high in carbohydrate (5). 

Despite these recommendations there is little if any evidence suggesting that there is any ‘minimum’ level of carbohydrate for health. Indeed the non-essentiality of dietary carbohydrate is not questioned, except by those who don’t understand the definition of essential in nutrition. 

There is no obligate requirement for carbohydrate in the diet as essential functions requiring glucose (for example glycolytic energy provision for red blood cells and neurons) are easily served via the creation of glucose from amino acids (from protein) and glycerol (the 'backbone' of fats), and almost all cells can utilise lipid derived fuels such as fatty acids via beta-oxidation (with the exception of cells lacking mitochondria such as red blood cells), and other cell types (such as neurons and cardiac tissue) have a high affinity for use of the ‘alternative’ fat-derived ketone body fuels (6). 

In spite of these high-carbohydrate recommendations from health organisations and government agencies for general and metabolic health, and for the treatment of cardiovascular diseases (CVD); low-carbohydrate, high-fat (LCHF) diets have shown promise for the treatment of obesity, diabetes and metabolic syndrome, neurological disorders, cancer, and have potential applications for heart disease prevention and may improve aspects of sports performance for some (7; 8) and so, LCHF and other low-carb diets should at the very least be recognised as a valuable addition to the toolbox of health practitioners and can be a viable option for those that are less active, or are less metabolically tolerant of carbohydrate. 

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​References:

1. Dietitians Association of Australia. (2013). Nutrient Reference Values.   Retrieved 10/3/2015, from http://daa.asn.au/for-the-public/smart-eating-for-you/nutrition-a-z/nutrient-reference-values-nrvs/

2. Roberts, D. (1999). Carbohydrates and Dietary Fibre: National Heart Foundation.

​3. World Health Organisation. (1998). Carbohydrates in Human Nutrition: World Health Organisation or the Food and Agriculture Organisation of the United Nations.
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4. Mann, J., Cummings, J. H., Englyst, H. N., Key, T., Liu, S., Riccardi, G., . . . Wiseman, M. (2007). FAO//WHO Scientific Update on carbohydrates in human nutrition: conclusions. Eur J Clin Nutr, 61(S1), S132-S137. 

5. Wheeler, M. L., Dunbar, S. A., Jaacks, L. M., Karmally, W., Mayer-Davis, E. J., Wylie-Rosett, J., & Yancy, W. S. (2012). Macronutrients, Food Groups, and Eating Patterns in the Management of Diabetes A systematic review of the literature, 2010. Diabetes Care, 35(2), 434-445

6. Westman, E. C. (2002). Is dietary carbohydrate essential for human nutrition? The American journal of clinical nutrition, 75(5), 951-953. 

7. Paoli, A., Rubini, A., Volek, J., & Grimaldi, K. (2013). Beyond weight loss: a review of the therapeutic uses of very-low-carbohydrate (ketogenic) diets. European journal of clinical nutrition, 67(8), 789-796. 

8. Sumithran, P., & Proietto, J. (2008). Ketogenic diets for weight loss: A review of their principles, safety and efficacy. Obesity Research & Clinical Practice, 2(1), 1-13. doi: http://dx.doi.org/10.1016/j.orcp.2007.11.003