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Soy has been singled out for attention among other legumes as a valuable source of nutrients, phytochemicals, and bioactive compounds. Early epidemiological studies established that whole soy and traditional soy foods were implicated in health-protective effects in Asian populations. The same benefits attributable to soy have not been consistently proven in Western populations that, for various reasons, opt to consume more processed soy foods or various soy components. Soy researchers continue to isolate soy components in search of identifying its salubrious components and whole soy remains relatively underinvestigated despite what we know of the health benefits it may confer to those regularly consuming it. Various dietary guidelines advocate the regular consumption of legumes that tend not to be included in our diets in sufficient quantities. This paper highlights the possibility that whole soy may have a more unique effect on health than a select soy component(s). It explores the rationale for focusing research on whole soy in an attempt to understand it better rather than trying to replicate the health benefits by targeting various soy components, which has been plagued by inconsistent results.

Soybeans are a good source of bone-healthy nutrients. Epidemiological studies in Asia evaluating diets containing traditional whole soy foods show a positive association with bone mineral density and fracture protection. Smaller scale intervention studies in Western nations mainly feature isolated soy protein (SP) and purified or concentrated soy isoflavones (SI) rather than whole soy foods and they have produced inconsistent results. Consumption of SP does not alter calcium (Ca) retention even though urinary Ca excretion is less in diets with SP compared with proteins higher in sulfur-containing amino acids. SI, often consumed at higher concentrations than would be available in traditional Asian diets, are not yielding the type of incontrovertible evidence that might be expected in support of their benefit to bone health. This forces one to ask whether whole soy might provide a superior effect on bone.

The philosopher William of Ockham is recognized for the maxim that an assumption introduced to explain a phenomenon must not be multiplied beyond necessity, or that the simplest explanation is probably the correct explanation. The general truth is that conjugated linoleic acids (CLAs) are nutrients. However, the demonstration that these isomers of octadecadienoic acid protect against cancers in rodents stimulated curiosity that directed significant resources to characterize the biological functions of these fatty acids in cell and animal models. The benefits to human subjects given supplements of CLA were at best modest. The disappointing results in humans should be taken as an opportunity to critically evaluate all findings of CLA use and to consolidate the common actions of this nutrient so that future investigations focus on specific isomers and the most reasonable mechanisms. As such, the principal and consistently reported benefits of CLA have been in improving cancer outcomes, reducing body fat in growing animals, and modulating cell functions. Recognizing where related actions of CLA converge in specific disease conditions and physiologic states is how research efforts should be directed to minimize the pursuit of superfluous theories. Here, we briefly review the current biological effects of CLA and attempt to integrate their potential effect on the physiology and health of the skeletal system. Thus, the purpose of this review is to advance the science of CLA and to identify areas of research in which these nutrients affect bone metabolism and skeletal health.

(n-3) PUFA deficiency and repletion effects on bone mechanical properties have not been examined. The primary research aim was to evaluate whether changes in the fatty acid composition of bone tissue compartments previously reported to influence bone formation rates would affect bone modeling and mechanical properties. In this investigation, three groups of rats were studied, second generation (n-3)-deficient, (n-3)-repleted, and a control (n-3)-adequate. The (n-3)-adequate diet contained alpha-linolenic acid [LNA, 18:3(n-3), 2.6% of total fatty acids] and docosahexaenoic acid [DHA, 22:6(n-3), 1.3% of total fatty acids]. Fatty acid composition of the hindlimb tissues (bone and muscle) of chronically (n-3)-deficient rats revealed a marked increase in (n-6) PUFA [20:4(n-6), 22:4(n-6), and 22:5(n-6)] and a corresponding decrease in (n-3) PUFA [18:3(n-3), 20:5(n-3), 22:5(n-3) and 22:6(n-3)]. Measurement of bone mechanical properties (energy to peak load) of tibiae showed that (n-3) deficiency diminished structural integrity. Rats repleted with (n-3) fatty acids demonstrated accelerated bone modeling (cross-sectional geometry) and an improved second moment in tibiae compared with control (n-3)-adequate rats after 28 d of dietary treatment. This study showed that repletion with dietary (n-3) fatty acids restored the ratio of (n-6)/(n-3) PUFA in bone compartments and reversed compromised bone modeling in (n-3)-deficient rats.