Carbohydrate tolerance in perspective – any justification for low carbohydrate diets?

Compiled by: Prof M Senekal, Division of Human Nutrition, Faculty of Health Sciences, University of Cape Town; Dr C Naude, Centre for Evidence-based Health Care, Faculty of Medicine and Health Sciences, Stellenbosch University; Prof E Wentzel-Viljoen, School of Physiology, Nutrition and Consumer Sciences, Faculty of Health Sciences, North-West University and Chair of the Professional Board for Dietetics and Nutrition

Dietary recommendations for health have been published and are regularly updated by the World Health Organization, United States of America and Canada (Institute of Medicine, Food and Nutrition Board), Europe (the European Food Safety Authority), the Nordic countries (National Food Safety Agency) and Australia and New Zealand (Australian and New Zealand Ministries of Health).

Within the context of energy balance for health and weight maintenance, these recommendations provide guidance on the macronutrientacomposition of dietsfor the prevention of chronic diseasesb in healthy populations (groups of individuals), while also ensuring adequate intake of micronutrientsc and other beneficial compoundsd in foods.These guidelines may also apply to healthy individuals who have metabolic risk indicatorse for chronic diseases,but do not apply to individuals diagnosed with such diseases.

Single “best values” for population level recommendations for healthy eating are seldom appropriate. It is for this reason that recommendations across countries specify “safe ranges” for macronutrient contributions to total energy intake. For carbohydrates the range varies between40 to 75%, for protein between 10 to 35% and for fatbetween 20 to 35%.As both quantity (% contribution to total energy intake) andquality (type and nature) of macronutrients areof importance, guidance on the quality aspects of carbohydrates and fats are also included in most recommendations.

Within the South African context these recommendations have been translated to the Food Based Dietary Guidelines published by the National Department of Health.fThis is recommended and encouraged by the World Health Organization for all countries.

Good quality carbohydrates provide energy, especially glucose for the brain, as well as vitamins, minerals,dietary fibreand other beneficial biologically active compounds. Food sources of good quality carbohydrates include unprocessed or minimally processed grains, legumes and fruits and vegetables.

Good quality proteins provide essential amino acids for body protein synthesis, as well as vitamins and minerals. Food sources of good quality proteins include fish, chicken without skin, lean meats, reduced fat dairy products andeggs.Qualityprotein can also be obtained from soyaand otherplant sources if combinedto ensure provision all essential amino acids e.g. samp and beans.

Good quality fat in the diet is necessaryto provide essential fatty acids, as well as for cell membrane integrity, hormone production,protection of organs, absorption of some vitamins and other functions.Foodsources of good quality fats include oily fish,plant oils, most nuts and seeds and avocado pears.

Any diet that is promoted for health should be sustainable in the long-term, specifically in terms of ease of adherence to guidelines, availability and affordability of foods, as well associal and cultural acceptability. Sustainability of dietary recommendations should also consider the total life-cycle greenhouse gas (GHG)emissionsg of the production, transportation and distribution of foods.

aMacronutrients: carbohydrate, protein and fat

b Chronic diseases: diabetes, coronary heart disease, stroke, cancer

cMicronutrients: vitamins and minerals

dOther beneficial compounds: fibre, biologically active compounds e.g. flavonoids, phytoestrogens…

e Metabolic risk indicators: poor glucose tolerance, high blood pressure, unhealthy blood lipid levels


gShifting from red meat and dairy toward chicken/ fish/egg or vegetable based diets for 1 day a week reduces GHG emissions substantially1

Nordic Nutrition Recommendations, 2006 2-3: The Nordic Nutrition Recommendations (NNR) are primarily valid for groups of healthy individuals. They can be used as guidelines for planning diets for groups, as a basis for teaching and dietary information, as a basis for food and nutrition policy and as a basis for evaluation of dietary intake.

Dietary Reference Intakes, United States of America and Canada, 2002/2005 4: The Dietary Reference Intakes include Acceptable Macronutrient Distribution Ranges (AMDR), defined as the range of intake for a particular energy source that is associated with reduced risk of chronic disease while providing intakes of essential nutrients. Consumption in excess of the AMDR confers the potential of increasing the risk of chronic diseases and insufficient intakes of essential nutrients. The AMDR is expressed as a percentage of total energy intake because its requirement, in a classical sense, is not independent of other energy fuel sources or of the total energy requirement of the individual. The Recommended Dietary Allowance for carbohydrate is set at 130 grams per day for adults and children based on the average minimum amount of glucose utilized by the brain.

Nutrient Reference Values for Australia and New Zealand, 2005 5: The Nutrient Reference Values include Acceptable Macronutrient Distribution Ranges (AMDRs) to reduce chronic disease risk whilst still ensuring adequate micronutrient intake. They are aimed at healthy people and may not meet the specific nutritional requirements of individuals with various diseases or conditions, pre-term infants, or people with specific genetic profiles. They are designed to assist nutrition and health professionals assess the dietary requirements of individuals and groups. They may also be used by public health nutritionists, food legislators and the food industry for dietary modelling and/or food labelling and food formulation.

Dietary Reference Values, European Food Safety Authority, 2010 6: The Dietary Reference Values apply to healthy populations and they are not intended as reference values for the treatment of patients with diseases or conditions like diabetes, obesity, or cardiovascular disease. However, they apply to healthy subjects with signs of metabolic disturbances like impaired glucose tolerance, elevated blood pressure, serum lipids, etc.

World Health Organization: Population nutrient intake goals for preventing diet-related chronic diseases, 20037:The WHO population nutrient intake goals represent the population average intake that is judged to be consistent with the maintenance of health in a population. Health, in this context, is marked by a low prevalence of diet-diseases in the population.


1. Weber CL, Matthews HS. Food-miles and the relative climate impacts of food choices in the United States. Environ Sci Technol. 2008 May 15;42(10):3508-13.

2. Becker W, Lyhne N, Pedersen AN, Aro A, Fogelholm M, Phorsdottir I, et al. Nordic Nutrition Recommendations 2004 – integrating nutrition and physical activity. Scandinavian Journal of Nutrition. 2004;48(4):178-87.

3. Nordic Council of Ministers. Nordic nutrition recommendations 2004. Integrating nutrition and physical activity. Arhus: Nordic Council of Ministers 2004.

4. Institute of Medicine Food and Nutrition Board. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients). Washington, DC: National Academies Press; 2002/2005.

5. Australian National Health and Medical Research Council and the New Zealand Ministry of Health. Nutrient Reference Values for Australia and New Zealand: Including Recommended Dietary Intakes. Canberra: Australian National Health and Medical Research Council and the New Zealand Ministry of Health2006.

6. EFSA Panel on Dietetic Products Nutrition and Allergies (NDA). Dietary Reference Values Parma: European Food Safety Authority (EFSA)2010.

7. World Health Organization/Food and Agricultural Organization. Diet, Nutrition and the Prevention of Chronic Disease. Report of a Joint WHO/FAO Expert Consultation. Chapter 5: Population nutrient intake goals for preventing chronic-diseases. Geneva: World Health Organization 2003.