Protein emerging as bone health factor

Moreover, new results suggest that both animal and plant source proteins could in fact benefit bones, countering established thinking that protein intake should be limited to protect bone health.

Researchers at the government-funded Agricultural Research Service are currently completing a third human clinical study investigating the impact of protein on bone health.

Their findings to date show that protein at both high and 'normal' levels have no impact on bone health markers. The new study shows that protein may actually increase calcium absorption when the mineral is at low levels.

"I think we're going to see the dogma that high protein diets harm calcium absorption reversed,"​ said Fariba Roughead, lead author of one of the latest studies in this area.

Nutritionists believe that protein may leach calcium from the bones as a result of the body's attempt to neutralize the acid ash or sulphate produced when protein is metabolized.

"Most of us don't eat enough alkali foods so the theory is that the body uses bone alkali, or calcium,"​ Roughead told NutraIngredients.com.

Yet studies carried out over the last two years suggest that the impact of protein on bones is in fact positive.

"This dogma [that proteins decreased calcium levels] was fuelled in the 60s and 70s with people testing purified proteins. But this is not a practical setting. We've been too reductionist,"​ suggests Roughead.

In 2003, the ARS team reported that a high-meat diet, consisting of 20 per cent of daily calories as protein, (about 117 grams, including 10.5 ounces of meat), had no adverse effect on calcium retention nor on biomarkers for bone breakdown in postmenopausal women, even when they were only receiving half the recommended calcium intake.

Last year a team from the Bone Metabolism Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University took the debate one step further, showing that protein could actually help bone health.

They reported that men and women who increased their dietary protein by an average of 58 grams of protein a day had 25 per cent higher levels of bone growth factor and lower levels of a marker of bone resorption compared with controls.

New results from the ARS team, not yet published, look set to confirm protein's benefit to bone health.

"We have tested 10 per cent and 20 per cent protein from both animal and soy. We have seen that higher protein intake from either source benefits people with low calcium levels,"​ said Roughead.

The team has however seen no benefit on calcium uptake from a soy isoflavone-rich diet.

But protein's benefit to bones could derive from another mechanism, such as through the insulin-like growth factor I (Igf-1), a hormone required for bone protection.

"IGF-1 levels increase when we feed higher amounts of protein to animals or humans. That's good news for bone,"​ explained Roughead.

Further research will be required to better understand this relationship but the research could significantly shape the functional foods market. Foods to boost bone health are forecast to grow by 7.6 per cent annually, reaching £86.4 million in the UK alone in 2007, according to Datamonitor.

Growth of such products will be driven by awareness of the bone-wasting disease osteoporosis, described by the World Health Organisation as the leading global healthcare problem after heart disease.

It currently affects 30 million people (predominantly women) worldwide and the number of related hip fractures is estimated to increase 135 per cent in the EU from 414,000 to 972,000 by the year 2050.