Cereals and Fibre in the diet

Cereals and Fibre in the diet

Prof HH Vorster, Centre of Excellence for Nutrition, North-West University

“Cereals must be one of the worst things parents give their children”. This is a recent unfortunate comment that received media attention as part of a campaign to promote low-carbohydrate diets. Unfortunate, because the South African Food-Based Dietary Guidelines (1) for adults and children over 5 years (previously 7 years) emphatically states that starchy foods should be the basis of most meals. The paediatric guidelines (2) advises that after 6 months of exclusive breastfeeding, babies should receive small amounts of solid foods, and at one year the basis of most of these small meals should be starchy foods. The “starchy foods” include cereals (mainly wheat, maize, rice, oats and sorghum in South Africa), legumes (dried beans, lentils, peas and soya) and some root vegetables such as potato, sweet potato and carrots. The technical support paper (3) which motivates and explain this guideline, following a scientific, evidence-based approach, emphasises that the starchy food sources, where possible and practical, should be in an “unrefined” or minimally processed form, to ensure that in addition to the energy-giving starch, also non-starch polysaccharides (dietary fibre) and many vitamins and minerals are contributed by these foods.

The purpose of this short contribution is to briefly list the benefits of cereal intake and to highlight, yet again, the possible detrimental short- and long-term health consequences of low-cereal, low-carbohydrate diets. The focus of this paper is on the role of cereals as a carbohydrate source in the diet, and not on the mono- and disaccharide sugars of which excess intakes are associated with potential overweight and risk of malnutrition.

There is little doubt about the beneficial health effects of cereal intake, especially whole grain cereals and cereal products for adults (4) and children (5). “Wholegrain cereal products” are those that contain 50% or more whole grain, although in some countries cereals with 10% or more whole grain are also regarded as whole grain). The beneficial effects are discussed in the following categories:

1. Dietary adequacy
Cereals are good sources of carbohydrate, notably starch, resistant starch fractions (RS) oligosaccharides (OS) and dietary fibre (DF). Children need sufficient energy for normal growth and development and the digestible carbohydrates in cereals provide this energy. In addition to providing essential carbohydrate for brain function (4, 5) cereals are also good sources of several vitamins and minerals and thus contribute to dietary adequacy (3-5).

2. Protection against non-communicable diseases
Diets high in cereals protect against the development of non-communicable diseases (NCDs) such as heart disease, diabetes, and some cancers when it replaces fat and especially saturated fat in the diet (3). In addition, the OS, RS and DF in cereals have beneficial effects on blood lipids. They also ensure that the glycaemic index of foods, meals and the total diet is low, protecting against insulin resistance and several NCDs. DF, OS and RS are fermented in the colon, contributing to health by effects on stool volume and frequency, beneficial bacterial growth, production of butyric acid to protect against colon cancer, absorption of calcium and strengthening of immune responses (3-5).

3. Variety and satiety: healthy food behaviours
Although there is controversy about the satiety value of specific foods and diets, there is some evidence that diets high in DF, OS and RS (and thus cereals) have a high satiety index and will contribute against intake of too much energy and overweight (4). Cereals furthermore bring variety into the diet and exposure of children to different cereals from an early age will help to develop healthy eating patterns (5). It should be emphasized that the amounts of sugars (mono- and disaccharides) added to cereals and cereal products should be limited to exert these beneficial effects. There are several breakfast cereal products on the market that contain unacceptable high amounts of sugars.

4. Affordability, traditional eating patterns
Cereals are staple foods in many countries because of its affordability. They thus became part of traditional eating patterns which are generally known to protect against NCDs (6). The adequacy and protein quality of traditional diets can be improved by adding sufficient amounts of legumes, vegetables, milk or fermented milk, or small amounts of peanuts and meat (chicken) to cereal-based diets (6). In any country struggling with poverty, food and nutrition insecurity and malnutrition, cereals and thus carbohydrate will form the largest part of energy intake, up to 70% of total energy, and it would be totally irresponsible to promote low-cereal, low-carbohydrate diets for such populations.

The scientific evidence for low-carbohydrate diets have been reviewed by several authors, including Bilsborough and Crowe (7) which clearly indicate that the weight loss achieved by low-carbohydrate diets can be ascribed to lower energy intake, and not specifically to low carbohydrate. Furthermore, these reviewers show from an analysis of the literature that low-carbohydrate diets are not sustainable; that they often do not contain sufficient fibre, thiamine, folate, vitamins A, E and B6, calcium, magnesium and potassium; that they may lead to ketosis, raised blood uric acid, dehydration, gastrointestinal symptoms, and hypoglycaemia. All these potential effects pose a serious health risk to individuals. The potential long-term effects include detrimental changes in serum lipids (increases in LDL-cholesterol and decreases in HDL-cholesterol) with an increased risk of cardiovascular disease, as well as mobilisation of calcium from bones (because of chronic metabolic acidosis) and consequent effects on bone health (7).

Cereals form an important part of the diet, especially in countries suffering from poverty, food and nutrition insecurity, and malnutrition. There are no good reasons to limit intake of cereals, (and specifically whole grain cereals without too much sugar added) in the diets of both children and adults. Low-carbohydrate diets have documented detrimental effects on health and risk of disease. If there are individuals that for some reason or other must follow a low-carbohydrate diet, necessary adjustments (increases) to vegetable and dairy intake should be made in an effort to increase dietary adequacy and the protective effects against NCDs.

1. Vorster HH, Love P, Browne C. Development of Food-based Dietary Guidelines for South Africa – The process. S Afr J Clin Nutr 2001; 14(3): S3-S6.

2. Bourne LT. South African paediatric food-based dietary guidelines. Matern Child Nutr. 2007; 3(4):227-229.

3. Vorster HH, Nell TA. Make starchy foods the basis of most meals. S Afr J Clin Nutr 2001; 14(3): S17-S24.

4. FAO/WHO. Joint FAO/WHO scientific update on carbohydrates in human nutrition. Eur J Clin Nutr 2007; 61(S1): S1-S137.

5. Stephen A, Alles M, De Graaf C, Fleith M, et al. The role and requirements of digestible dietary carbohydrates in infants and toddlers. Eur J Clin Nutr 2012; 66: 765-779.

6. Vorster HH, Venter CS, Menssink E, Van Staden DA, Labadarios D, Strydom AJC, Silvis N, Gericke GJ, Walker ARP. Adequate nutritional status despite restricted dietary variety in adult rural Vendas. S Afr J Clin Nutr 1994; 7(2):3-16.

7. Bilsborough SA, Crowe TC. Low-carbohydrate diets: what are the potential short- and long-term health implications? Asia Pacific J Clin Nutr 2003; 12(4): 396-404.