Rethinking the Acceptable Macronutrient Distribution Range for the 21st Century: A Letter Report (2024)
Chapter: 5 Concerns about the Acceptable Macronutrient Distribution Range
5
Concerns about the Acceptable Macronutrient Distribution Range
CONCERNS ABOUT USE OF THE AMDR IN APPLICATIONS
The committee identified two primary concerns about the Acceptable Macronutrient Distribution Range (AMDR). One concern is the subjective nature of the evidence base supporting establishment of the AMDR values. Additionally, emerging evidence over the past two decades has shown that qualitative considerations, such as protein source with differing amino acid profiles, or consuming more complex rather than simple carbohydrates, may be at least as important as following quantitative macronutrient intake guidelines.
Nature of the Process
The strength of the evidence to support the AMDRs was not well documented and appeared to be variable among AMDR values. The narrative reviews lacked standardized protocols applied to each of the macronutrients (IOM, 2002/2005); this approach predated the standardized protocols currently in place, including the risk assessment approach.
Consequently, many nutrition and public health practitioners find it challenging to interpret intakes that fall outside the AMDR range. When the AMDRs have been applied to assess distributions of usual intake in the population, substantial proportions of the distributions for some sex- and life-stage groups have sometimes been observed outside these ranges. Whether intervention is warranted in the face of such deviations is unclear because of the limited evidence base underpinning the AMDRs.
Similarly, in applications at the individual level, the level of risk associated with usual intakes that are near or just outside of the AMDR range is difficult to predict. While the AMDRs are applied by some dietary intake planners, this report identified changing conditions that support consideration for alternative approaches.
Macronutrient Distribution and Quality
Advances in understanding the biological role of macronutrients, and particularly macronutrient quality in health outcomes have likewise expanded. As a result, for the most part, dietary guidance now emphasizes the quality of macronutrients rather than total quantity of macronutrients, with no reference to total amount (Lichtenstein et al., 2021; USDA and HHS, 2020).
The AMDR recommendations did not address the possibility that, within the context of a constant energy intake, relative proportions of macronutrients could vary widely. Figure 5-1 illustrates how the percentage of calories of carbohydrate and fat could differ substantially and still fall within the recommended AMDRs for a particular age group. If the quality of one or more of the macronutrients was poor, for example high in refined carbohydrates or predominant in low quality protein, and the intake of that macronutrient was at the lower range of the AMDR, there might be a higher risk of nutrient insufficiency.
Further, for each of the macronutrient categories, there could be a substantial range in the quality of its components. For example, recommendations for carbohydrates should include carbohydrate type (unrefined, refined), structure (simple, complex) and fiber content (see Figure 5-2). Within the total protein category, consideration should be given to amino
NOTES: MUFA = monounsaturated fatty acid; PUFA = polyunsaturated fatty acid; SFA = saturated fatty acid.
acid profiles within the context of essential and nonessential distributions. For example, consumption of poorer quality protein, even at the higher AMDR range (as a percent of energy intake), may not meet the requirements for essential amino acids, especially in persons with lower energy intake, such as with some older adults or individuals on weight-loss diets (Moughan et al., 2024). Within the total fat category, consideration should be given to the distribution among major subclasses, saturated fatty acids (SFA); monounsaturated fatty acids (MUFA); and polyunsaturated fatty acids (PUFA); essential fatty acids, fatty acid isomers (n-3 and n-6), and their conformation (cis and trans); and potentially cholesterol and other sterols. These quality considerations were primarily absent from the AMDRs.
AN ALTERNATIVE FRAMEWORK TO THE AMDRs
The Dietary Reference Intake (DRI) framework, proposed in 1994, provided a statistical model for assessing requirements (Estimated Average Requirements [EARs]/Recommended Dietary Allowances [RDAs]) and an approach for setting values for Tolerable Upper Intake Levels (ULs) (IOM, 1994) (see Chapter 3 and Figure 3-1). The framework recommended inclusion of concepts related to the reduction in the risk of chronic disease. Subsequent DRI review committees found it difficult to apply the derivation of the EAR/RDA and UL as DRI values to risk of chronic disease.
Additionally, the type of intake/response curves available to establish the EAR and UL values differed from those available to set reference values for chronic disease risk reduction. In response to the methodological challenges inherent in setting a DRI value, a new approach to deriving a DRI value specific to chronic disease risk was proposed in the report Guiding Principles for Developing Dietary Reference Intakes Based on Chronic Disease (NASEM, 2017). This report provided standards for evaluating the types of evidence needed to assess relationships between dietary intake and risk of chronic disease. The report also discussed the variable and complex nature of intake/response curves in which the slopes defining risk could vary directionally and in curvilinearity as defined by the strength of evidence at specific intake levels. The report recommended, on a theoretical basis, the use of ranges for expressing reference values related to risk of chronic disease.
When the DRIs for sodium and potassium were updated in 2019, the recommendations from the Guiding Principles report were used, in part, to establish a new DRI, the Chronic Disease Risk Reduction (CDRR) value (NASEM, 2019). The CDRR was established for sodium based on evidence for a beneficial effect of reducing sodium intake on risk of cardiovascular disease, hypertension, and systolic and diastolic blood pressure. The CDRR evaluated the intake/response curves to establish a level of sodium intake below which chronic disease risk would be reduced within the apparently healthy population. Based on the nature of the evidence available, a point estimate was used rather than a range for setting the CDRR for sodium.
SUMMARY
Clearly, the science has evolved over the past decades. The limitations to the original AMDRs are now apparent, including both the process and the considerations of macronutrient quality. With the addition of an approach as exemplified in the Guiding Principles report (NASEM, 2017), there is now well-documented criteria for evaluating the sufficiency of the evidence in support of chronic disease outcomes (e.g., CDRR).
