Foundations for practical nutritional information

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Several characteristics of nutritional information for evidence-based food choices for health, are summarized below and will be illustrated with reference to data sets for managing blood glucose (Table 7.2) and large bowel function respectively (Table 7.3). In a nutshell, health end-points need to be selected, markers

Table 7.2 Developing nutritional data sets related to health end-points associated with elevated blood glucose

Consideration Relevance to blood glucose

End-points

Intermediate end-point or marker of effect

Currently used indices

Relevant index

Practical units

Validation

Disorders from glycation and glycaemia, including vascular disease of retina, kidneys, nerves. Heart disease. Polyuria.

Postprandial glycaemic response: blood glucose elevation underlies many long term complications of diabetes mellitus, involving hyperinsulinaemia and glycation.

Sugars and available carbohydrate: not dependable indicators of blood glucose response, which depends on digestion rate of available carbohydrates and on their monosaccharide composition. Glycaemic index (GI): A percentage based on glycaemic response to food carbohydrate compared with response to glucose. Use restricted to equicarbohydrate comparisons and does not respond to food intake. Not useful for accurate blood glucose control.

Relative glycaemic potency (RGP):58 A percentage based on comparison of food with glucose. RGP ranks whole foods by their glycaemic impact on an equal weight basis, but does not respond to food intake. Suitable for food comparisons on an equal weight basis.

Glycaemic glucose equivalents (GGE):44 Derived from RGP. A measure of glycaemic impact based on foods. Responsive to food quantity. Useful for communicating efficacy. Can be applied to food items of any weight.

Clinical measurements have shown that GGE intake predicts glycaemic response to foods of different GI, carbohydrate content, and intake at carbohydrate doses consumed in most meals.61

identified that can be causally linked to the end-points, valid indicator variables that predict changes in markers identified for practical tests, and measurements communicated so they can be easily understood.

7.4.1 End-points that are important to well-being

A number of health and disease end-points, affecting a large proportion of the population, need to be addressed in developing healthy foods. Some, such as cardiovascular disease, colorectal cancer, osteoporosis, and constipation are associated with a combination of ageing and unhealthy dietary patterns. Others, such as obesity, are largely the result of food processors and marketers successfully providing foods that appeal to the basic human preferences for sweetness and fats, in all age groups. It would be best to design foods with a number of endpoints in mind, and evaluate them with a battery of tests to demonstrate nutritional balance. Producing foods for specific functions or using foods as medicines risks unbalanced nutrient intake.

7.4.2 Biomarkers that are relevant38

To be health-relevant and useable, food information needs to relate to practically measurable but valid markers linked to health end-points,10,38 such as blood cholesterol in relation to cardiovascular disease,39 or alterations in faecal components

Table 7.3 Developing nutritional data sets related to health end-points associated with insufficient faecal bulk

Consideration

Relevance to faecal bulk

End-points

Intermediate end-point or biomarker

Currently used index

Relevant index

Practical units

Validation

Various large bowel disorders including constipation, diverticulosis, colorectal cancer.

Faecal mass, representing distal colonic bulk.

Dietary fibre: does not reliably predict faecal bulk because bulking effects depend on fermentability, water holding capacity and bacterial growth.

Faecal bulking index (FBI):34 The impact of a whole food on faecal bulk as a percentage of the effect of an equal weight of wheat bran. Usable for measuring efficacy on an equal weight basis.

Wheat bran equivalents (WBEfb):42 Expressed as a content in foods. May be used to communicate relative efficacy. Applicable to food items of any weight.

Faecal bulking response measured as mass of rat faecal pellets after hydration closely reflects response in humans.85

in relation to colon cancer,40 and to be obtained with standardised procedures that can be applied to a wide enough range of foods for comparisons to be made.

Biomarkers are required because human death, disease and sub-optimal health are not permissible dependent variables, and many are the result of cumulative changes over long periods. Instead, intermediate biomarker 'end-points', markers of exposure to a food component, and food properties that research has already established as causal in disease and health must be used to assess health effects of food processing. Intermediate end-points must be either causal factors or correlated with changes that lead to end-points. For instance, hyperlipidaemia is an intermediate biomarker that is causally related to a true end-point -atherosclerosis.39 However, as many factors are involved, evidence for the benefit of a product would be more convincing if several relevant biomarkers were measured. At present most biomarkers require clinical or laboratory measurement and are not widely used to monitor nutritional changes in the course of product development. A good deal of further work is required to develop tests that are useful to industry.

7.4.3 Validity that is balanced with practicality

Validation is a crucial step in selecting variables that indicate effects of foods and food processes on biochemical precursors of health end-points. Because most foods are complex systems, ideal experimental trials in which one food factor is varied while all other variables are kept constant are not often possible, and there is a need to balance practical requirements of food processing with degree of nutritional validation. Given that final products should be comprehensively evaluated, progress in food processing will often best be maintained by being prepared to sacrifice some degree of validity for expediency by appropriate choice of tests, as discussed in section 7.2.3 and illustrated in Table 7.1.

7.4.4 Nutrition information that is up-to-date

Nutrition science is constantly advancing, and as hard data throws new light on the relationship between a food property or component and a health end-point, indices of food effects on health are likely to change. For instance, heart disease is now considered to be influenced less by intake of fat than by intake of specific fatty acids such as saturated and trans-fatty acids.41 Such changes are not a sign that nutrition science cannot be relied on but that continuing research leads to clarification.

A food company that had not kept abreast of nutritional knowledge recently formulated a new 'diabetic muesli bar', replacing all sucrose sources with dextrins, in the belief that 'sugar' replacement would improve blood glucose control. However, such wisdom was obsolete, because sucrose, being half fructose, induces a much lower blood glucose response than dextrins, which are rapidly digested glucose polymers. The new 'diabetic' bar had a greater glycaemic impact than the unmodified version.

7.4.5 Relevant indices that are based on factors that confer relevance on food data

The relevance of food information is determined by validity, sufficiency, practicality, and communicability. Is an index a true reflection of a change in a biomarker or end-point, is it sufficient on its own to predict a change in the end-point, is it a variable that can be measured easily, and expressed in terms that users understand well enough to use in food choice?

7.4.6 Food data that is easily understood

Food data is not relevant if it cannot accurately link consumer behaviour to health end-points, in other words, if it cannot guide food choice for health. To do so it should be easily used. The relative efficacy of foods may, for instance, be expressed in terms of equivalents to a familiar reference that exhibits a specified effect to a known degree, as in wheat bran equivalents and faecal bulking.42 Gly-caemic index (GI), on the other hand, is an example of a number that is supposed to represent the glycaemic potency of a food.43 However, unlike intake of a nutrient, GI does not change with the composition, serving size, or intake of food, so it makes little sense to consumers, and cannot be used accurately to modify eating patterns that affect blood glucose.44

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