Is vegetable protein more beneficial to bone than animal protein?
Introduction
Public health strategies aimed to target, on a population-wide basis, the prevention of poor bone health throughout the lifecycle are urgently required given the certainty of prediction that hip fractures will rise dramatically over the next decade and beyond. Clearly, nutrition (as an exogenous factor) has a crucial role to play in the optimization and maintenance of skeletal integrity. It is essential that specific dietary lifestyles, such as the particular inclusion or exclusion of particular foods/food groups within the overall diet, are carefully monitored to ensure that any such regime does not place the individual/population group at an increased risk of osteoporosis or its associated risk factors.
The term ‘vegetarian’ is non-specific. It can often be used to describe a whole range of diets, practiced with varying degrees of restriction. Vegetarians may be referred to as ‘semi/demi’-vegetarian, if they merely exclude meat [1]. Other categories include: lacto-ovo-vegetarian, if they exclude meat, fish and poultry but eat eggs and milk products; lacto-vegetarian, if they exclude all animal foods except milk and milk products; and vegan, if they exclude all foods of animal origin. Vegetarianism has become particularly popular in recent years. In the UK, approximately 4.3% of the population (equivalent to roughly 1:20 people) state that they follow a vegetarian diet, with young women being particularly represented; approximately one in four women aged 16–24 years avoiding red meat [2].
Since adolescence is a critical time with respect to bone health, individuals need to ensure that there are sufficient intakes of energy, calcium, iron and vitamins B12 and D given the required extra nutritional demand [3]. However, a well-planned varied vegetarian diet has been shown to be consistent with good health and there is data to suggest that following such a regime can potentially reduce the risk of chronic disease.
Section snippets
General concepts
There is evidence to show that vegetarianism is associated with several factors which are likely to have a detrimental impact on bone including lower circulating levels of oestrogen and a lower average body mass index [4]. Additionally, with the recognition of the potential criticality of acid–base balance to skeletal integrity, it was considered that long-term ingestion of ‘vegetable-based’ diets may have a beneficial effect on bone mineral density (BMD) [5].
Criticality of acid–base homeostasis to health
Acid–base homeostasis is critical
Studies in Eskimo populations
Little data is available on bone health in populations consuming a diet highly dependent on animal foods, particularly that of meat. Mazess and Mather [17] examined forearm bone mineral content (BMC) in a sample of 217 children, 89 adults and 107 elderly Eskimo natives of the north coast of Alaska. Eskimo children were found to have a 5–10% lower BMC than US white children, a finding which was consistent with smaller body and bone size. In the young Eskimo adult population (age range
Concept of dietary ‘acidity’: potential renal acid load (PRAL)
The potentially deleterious effect of specific foods on the skeleton has been a topic of recent debate [33], [34]. If the acid : base/skeletal link is to be believed, a possible explanation for there being no difference in indices of bone health between vegetarian vs. omnivorous populations, is that vegetable-based proteins generate a large amount of acid in the urine. Work by Remer and Manz [35] on the potential renal acid load (PRAL) of foods has shown that many grain products and some cheeses
Animal vs. vegetable protein intake: impact on bone
Ecological studies have shown that world-wide per capita consumption of animal protein has been associated with a higher risk of hip fracture in women aged > 50 years [36]. More recently, the correlation has been shown to be stronger with the ratio of animal protein to vegetable protein, a study which has adjusted for important cultural differences [37]. It is important to note, however, that in these correlational studies, the unit of measurement is country and not individual and as such, these
Fruit and vegetable link to bone: other potential mechanisms of action?
There are growing data, both observational and experimental which show a positive link between fruit and vegetable consumption and bone health [47], [48]. However, more intervention studies are required before a causal link can be claimed. Furthermore, it remains to be determined the exact mechanisms behind a fruit and vegetable link to the skeleton since these foods provide not only a source of dietary alkali but also a wide variety of micronutrients, many of which have plausible workings for
Discussion
There is a clear and urgent need for public health strategies to target prevention of poor bone health on a population-wide basis and, similarly, it is critical that particular dietary habits resulting in the exclusion of specific foods are carefully monitored to ensure that population groups are not placing themselves at an increased risk of osteoporosis or its associated risk factors.
Existing and available data indicate that consumption of a lacto-ovo-vegetarian does not have an over-riding
Conclusion
The impact of a ‘vegetarian’ diet on bone health is a hugely complex area for the following reasons: 1) components of the diet (such as calcium, protein, alkali, vitamin K, phytoestrogens) may be varied; 2) key lifestyle factors which are important to bone (such as physical activity) may be different; 3) the tools available for assessing consumption of food are relatively weak. However, from data available and given the limitations stipulated above, ‘vegetarians’ do certainly appear to have
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