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Animal protein builds muscle mass – plant protein doesn't

Animal protein builds muscle mass – plant protein doesn't
Women who eat vegetarian are dependent for building muscle on – paradoxically – the amount of animal protein in their diet. Finnish health scientists from the University of Helsinki write this in an article that will soon appear in the British Journal of Nutrition. It's too bad for vegans, but plant proteins are not good muscle builders.

The Finnish population is ageing and is slowly going over – like the rest of the world – to vegetarianism. Is this likely to lead to problems? That's the question behind the researchers' study. As elderly people lose muscle mass – and women are more vulnerable when it comes to this than men – they become less able to look after themselves. Because a vegetarian diet means fewer building blocks for muscles, the researchers are concerned that vegetarian women especially are at risk of losing their independence as they get older.

To find out whether their concerns are founded, the Finns measured the body composition of a grand total of 1 vegan woman, 10 lacto-vegetarian women and 8 lacto-ovo vegetarian women. They compared the data with the body composition of 21 meat eaters. The vegetarians had been meatless for an average of twelve years.

The vegetarians had 4.4 kg less muscle mass than the omnivores, the researchers discovered.

Animal protein builds muscle mass – plant protein doesn't

When they examined the women's blood they noticed that vegetarianism results in up to fifty percent higher concentrations of the binding protein SHBG. SHBG neutralises the muscle building hormone testosterone. But after doing their calculations the researchers concluded that the higher SHBG level does not explain why vegetarian women have less muscle mass than meat eating women.

When the researchers analysed the women's diets, they noticed that it was above all the amount of animal protein that determined how much muscle the women had.

Animal protein builds muscle mass – plant protein doesn't

Plant protein had no effect. To give you a better idea of the women’s diets: all women in the study consumed about one gram of protein per kg bodyweight per day. For the vegetarian women, about 0.54 g of this figure was animal protein. For the omnivore women the figure was 0.71 g.

The researchers suspect that while many traditional plant protein sources, like legumes and grains, contain amino acids on paper, the body doesn't actually absorb these well in practice. Another possibility is that plant protein has a less anabolic effect because plant proteins contain less of the amino acids leucine, methionine and lysine. Muscles need these amino acids. Leucine especially is important for muscle building. Muscle cells work their anabolic machinery harder the more leucine they get. Leucine is what makes the muscles cells 'see' that they are getting lots of amino acids.

The researchers admit that their study was very small. But they say the results are serious enough to do further research on whether elderly vegetarian women lose more muscle power.

In 2007 researchers at Sherbrooke University also reported that older women have more muscle mass the more animal protein they eat. [J Nutr Health Aging. 2007 Sep-Oct;11(5):383-7.] But it seems that not all plant proteins work in the same way. There are studies that show that soya proteins have just as much anabolic effect as animal proteins. [J Int Soc Sports Nutr. 2007 Jul 23;4:4.] Laboratory animals given only protein from lentils and beans experience a decrease in muscle mass. [Ann Nutr Metab. 2006;50(3):197-205.]

Br J Nutr. 2009 Aug 14:1-8. [Epub ahead of print].

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