Other Dietetically Important Factors

The need to include a variety of minerals in experimental diets has already been mentioned this was especially stressed (1920-1930) by Boyd-Orr, the director of the Rowett Institute for Animal Nutrition in Scotland. Increasingly refined food sources led to the identification of large numbers of trace elements (e.g., Cu, Mn, Mo, Zn) whose importance in the diet was suggested from hydroponic experiments with plant seedlings. Cobalt is an example of such a trace element. Vitamin Bj2 is synthesized by bacteria in the rumens of sheep and cattle but is absent from their fodder. In Australia, sheep feeding on cobalt-deficient pastures failed to thrive because vitamin B12 could no longer be made. 

The last essential dietary components to which we will refer and which were also discovered through feeding experiments with rats, are certain unsaturated fatty acids identified as linoleic, linolenic, and arachidonic acids by Burr and Burr in 1930. The acids are required for the formation of complex lipids which are essential in membranes for the maintenance of their fluidity (Chapter 9). Deficiencies lead to a dermatitis which does not respond to additional B vitamin supplements or to oleic acid. 

---

According to some authors, the dietetic cholesterol is absolutely the most important factor in establishing the levels of blood cholesterol, according to others, it is responsible only for 60-80% of the latter. According to KEYS (18), exogenous cholesterol increases the serum levels in proportion to the square-root of its concentration in the diet. 

---