DEFINE MACRO NUTRIENTS PLUS

If a benefit or adverse effect is seen, it is not immediately clear what is responsible for the observed outcome.

For example, in assessing the effects of a high carbohydrate diet on a specific endpoint, the test diet must be relatively low in fat and/or protein and/or vary in its energy content. Studies of individual macronutrients are particularly prone to confounding by the other necessary changes to the diet (ie either the energy content changes in the control group and/or the proportion of other macronutrients). Randomised controlled trials, which provide the most conclusive evidence of causality, are often lacking in relation to optimising macronutrient profile. Much of the evidence is based on epidemiological studies with clinical endpoints but these studies generally show associations rather than causality and are often confounded by other factors that can affect chronic disease outcomes.

DEFINE MACRO NUTRIENTS PLUS

In their document, they extensively reviewed the current evidence, in terms of outcomes such as body weight maintenance, obesity, CHD and LDL oxidation, stroke, Type 2 diabetes, hyperinsulinaemia and glucose tolerance, metabolic syndrome, cancer, osteoporosis, renal failure, renal stones, inflammatory disorders and risk of nutrient inadequacy in adults, as well as some of these outcomes, plus birth weight and growth in relation to children. The Food and Nutrition Board of the Institute of Medicine in constructing the US:Canadian Dietary Reference Intakes (FNB:IOM 2002) called this range the Acceptable Macronutrient Distribution Range (AMDR). The risk of chronic disease (as well as the risk of inadequate micronutrient intake) may increase outside these ranges, but often data in free-living populations are limited at these extremes of intake. There appears to be quite a wide range of relative intakes of proteins, carbohydrates and fats that are acceptable in terms of chronic disease risk.

This has not always been given enough consideration in study design or interpretation. However, the form of fat (eg saturated, polyunsaturated or monounsaturated or specific fatty acids) or carbohydrate (eg starches or sugars high or low glycaemic) is also a major consideration in determining the optimal balance in terms of chronic disease risk. There is a growing body of evidence that a major imbalance in the relative proportions of macronutrients can increase risk of chronic disease and may adversely affect micronutrient intake. Thus, for example, a high fat diet is usually relatively low in carbohydrate and vice versa and a high protein diet is relatively low in carbohydrate and/or fat. For a given energy intake, increases in the proportion of one macronutrient necessarily involves a decrease in the proportion of one, or more, of the other macronutrients. The effect of alcohol on health outcomes has been reviewed elsewhere and will not be revisited here except to say that alcohol intakes below about 5% of dietary energy are recommended (NHMRC 1999, 2003). Alcohol can also contribute to dietary energy. Unlike the micronutrients, the macronutrients (proteins, fats and carbohydrates) all contribute to dietary energy intake.

Define macro nutrients