What is a healthy diet?

Last week’s note showed that the UK dietary advice is nutritionally deficient. The recommended diet is so low in fat that it does not deliver the fat soluble vitamins (A, D, E, K) and it also missed out on calcium. Low fat dietary advice in the US, Australia, NZ and other nations is therefore also likely to be nutritionally deficient.

The obvious follow-up to last week’s note is to present a diet that would deliver recommended intakes of micronutrients. There is a caveat – we don’t know if the Dietary Reference Intakes are accurate. Recommended Dietary Allowances (RDAs) have been prepared by the American National Academy of Sciences Food and Nutrition Board since 1941. The first edition was published in 1943 to provide ''standards to serve as a goal for good nutrition” (Ref 1).

The measurements collectively called the Dietary Reference Intakes (DRIs) include four guides: Recommended Dietary Allowance (RDA); Adequate Intake (AI); Tolerable Upper Intake Level (UL); and Estimated Average Requirement (EAR). For example, until the end of 2010, the vitamin D recommendation in the US was that 10mcg per day was an Adequate Intake. This was revised in November 2010 when the vitamin D recommendation became a DRI, rather than an Adequate Intake, and this was set at 15mcg per day (Ref 2). At the same time, the Tolerable Upper Intake Level (not to be exceeded) was set at 100mcg per day for vitamin D.

The National Academies publication reports six types of evidence used to establish the recommended intakes: (1) studies of people consuming low levels of a nutrient, followed by observation of measured increases in that nutrient; (2) nutrient balance studies that measure nutrient levels in relation to intake; (3) testing nutrient levels in human tissue in relation to nutrient intake; (4) nutrient intakes of fully breastfed infants and of apparently healthy people from their food intake; (5) observations of health and nutrient status in populations in relation to intake; and (6) in some cases, extrapolation of data from animal experiments (Ref 3).

The caveat about the accuracy or otherwise of DRIs need not worry us since we are reviewing the recommended daily amount, which is taken as the lowest level of intake that will maintain sufficient nutrition for an individual. If the guidelines were set at a high bar, missing them may not be an issue. Given that they are set at minimum levels, missing them is likely to be an issue. The exercise that follows, therefore, seeks to establish a daily basket of foods that can deliver at least these minimum amounts.

The foods that deliver recommended intakes

 

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