Sources of Dietary References and Data

Reference Intakes

A Dietary Reference Intake is the amount required or believed to prevent disease in 97-98% of a population. Since about 15% of people have at least one existing health problem, these intakes provide a margin to cover all but those with specific high-risk difficulties. Usually, they are about double what is required by those in perfect health.

Some nutrients are required in small quantities but are toxic or cause other health problems in excess. Some have formal Tolerable Upper Limits. Vitamins A & D are the most common concern in this respect, but B3 and B6 must also be watched.

Optimal intakes, those that might produce the best possible health, are subjects of considerable disagreement and hyperbole, and are not dealt with here.

The reference intakes used in my diet studies are for a male over 50 years of age, which I am. They mostly come from the US National Academy of Sciences. The upper limit on sodium is from the US 2005 dietary guidelines. For calcium, in view of widespread criticism of the NAS value, I use European recommendations. Given the proximity of the skeletal fluorosis level to the NAS DRI for fluoride, I subtract 1 mg since Ottawa water is fluoridated and treat it as a maximum; even so it may be high.

The saturated and monounsaturated lipid references are each for 10% of calories in a 2000 calorie/day diet, figures widely accepted in dietary guidelines.

There are two major views of omega-3 lipids: 1, that they form a large part of the lipids in our brain, which should be accumulated in childhood and maintained in adulthood; 2, that they reduce cardiovascular problems and possibly inflammation as well. ISSFAL recommends 0.5 g/day of EPA+DHA plus 1.5 g/day of ALA; NAS lists an RDI of 1.6 g ALA. My reference is equivalent to ISSFAL: the sum of 20:5n3 (EPA), 22:5n3 (DPA) and 22:6n3 (DHA), plus 18:3n3 (ALA) divided by 10 to allow for the limited conversion of this short-chain lipid to the long forms required by our brain.

There are also two major views of 18:2n6 (LA): 1, that it is a necessary nutrient to prevent the body production of 20:3n9 (Mead's acid) that occurs when LA is less than 1% of total calories; 2, that an excess of omega-6 interferes with metabolism of omega-3. I prefer the latter view for those with normal gastrointestinal health and modern diet which is so high in LA, so treat omega-6 lipids the same way as omega-3 - 18:2n6 (LA) is divided by 10 then added to the sum of all long-chain non-omega-3 lipids, and a resultant 6/3 ratio of four used to determine an upper limit. This limit is above the minimum recommended by agencies who prefer view 1, such as the NAS who list 14 g LA, equivalent to 1.4 g omega-6 in my system.

The protein and amino acid references are those of the NAS, with their individual amino acid recommendations multiplied by 1.56 so that their sum matches their total protein recommendation in the same ratio as is found in our bodies.

The dietary cholesterol limit is recommended by several US authorities, as is the level for dietary fiber. The recommendation for lutein+zeaxanthene comes from the American Optometric Association, among others. The flavonoid level results in a factor of two decrease in cardiovascular disease according to the Seven Countries Study; it includes flavonols, flavones, flavanones, flavan-3-ols, isoflavones, anthocyanidins and proanthocyanidins. The limit on mercury is from FAO.

Some conversions: divide Vitamin A International Units (IU) by 3.33 to get retinol equivalent in µg; divide beta-carotene µg by 12 to get retinol equivalent in µg (but by 3.33 if it's expressed in IU); divide Vitamin D IU by 40 to get µg cholecalciferol; divide Vitamin E IU by 1.5 to get alpha-tocopheral equivalent in mg; divide the mg/dl used in the USA for serum cholesterol levels by 39 to get the mmol/l used internationally.

Dietary Data

My data on food nutrients comes almost entirely from the United States Department of Agriculture Nutrient Data Laboratory.

Values for Vitamin D vary considerably by location and time of year, and the USDA rarely tests for it. I rely primarily upon the Finnish National Public Health Institute (Fineli) Nutrition Unit Food Composition Database and the Danish National Food Institute (DNFI) Food Composition Databank, but there was also some North American data at the USDA that has been deleted from their current database.

The USDA does not report at all on iodine, citing its variability. There is data on iodine content of individual foods at Fineli and DNFI, also average values that were published by Deakin University. The data is so variable depending upon soil, and whether iodised salt is used in animal feed and for processed products such as cheese, that I use averages based on the Fineli and DNFI data. (The Deakin averages are much higher than those at Fineli and DNFI, especially for vegetables.)

For fluoride, there is some data at the USDA. References to studies were provided by the BC government, but the ranges as they quoted them are too wide to be of use for diet planning, although North American values tend to be on the low side of their ranges. I must warn here against using any data from a site involved with municipal water fluoridation, as both sides in that debate have moved to such extremes that neither is trustworthy. (For example, the Parents of Fluoride Poisoned Children site presents solely the maximum values that have been measured anywhere in the world, and doesn't say so.)

The only source of data I have found for biotin is at DNFI.

Data for mercury in fish is available from the FDA.

Although there are RDI's listed for chloride, there is almost no data available. However, what there is indicates that it parallels sodium content.

John Sankey
other notes on nutrition