Vegetarians and vegans appear to be protected from certain diseases by the exclusion of meat from their diets. For example, certain cancers of the digestive tract may be induced by high intakes of meat and vegetarianisms protects the individual by lowering risk. Comparisons between vegetarians, vegans and meat eaters can be a useful tool to researchers when assessing the impact of nutrition on individuals. For example, researchers1 have assessed the impact of a vegetarian, vegan, fish or meat diet on the risk of bone fractures in 7947 men and 26749 women. The fracture incident rate ratios compared to meat eaters were 1.01 for fish eaters, 1.00 for vegetarians and 1.30 for vegans. When the researchers equalised the calcium intakes for the different groups by only including subjects with intakes of at least 525 mg of calcium a day, the fracture rates for the vegans where not significantly different between groups.
Low calcium intake therefore might contribute to the high fracture rate in vegans. However, research seems to suggest that increased calcium intake has little effect on bone health. Recent evidence suggests that bone health is associated strongly with the acid base balance of the individuals diet and with sufficient vitamin D intake. Protein foods contain certain amino acids that form acidic compounds (e.g. sulphuric acid) in the circulation and this can cause the resorption of alkali bone minerals in an attempt to neutralise the hydrogen ions. Plant foods contain high levels of potassium salts that form alkali compounds (e.g. bicarbonate) in the blood and thus maintain a higher plasma pH which may prevent long-term bone loss. However, there is little evidence to suggest that vegans consume less fruits and vegetables than meat eaters, and so this does not explain the increased fracture rate.
Vegans have lower protein intakes when compared to vegetarians and particularly meat eaters. While excess protein in the absence of fruits and vegetables can shift the balance of pH in the blood towards acidic conditions, too little protein is suspected of decreasing insulin-like growth factor-1 which then suppresses osteoblast formation and slows bone growth. Vegans are also known to have low intakes of vitamin D, perhaps because sources of vitamin D such as milk and other dairy products are absent from their diet. Dietary intakes of vitamin D are not predictive of vitamin D status because sunlight is able to raise plasma levels of 25-hydroxyvitamin D. However, evidence suggests that 25(OH)D levels in many people living at high latitudes are insufficient for optimum health, and this data combined with their low dietary intake suggests that vegans are at risk of vitamin D deficiency, which may account for their high bone fracture rates.
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