Protein, leucine and muscle wasting: ‘It’s an on/off switch, not a dimmer’

Professor Douglas Paddon-Jones from the University of Texas’ department for nutrition and metabolism told us that protein and leucine could be a practical and affordable solution for sarcopenia, the degenerative loss of skeletal muscle mass, quality and strength associated with ageing, injury or illness.

According to the results of his study​ published in the Journal of Nutrition ​back in January, the consumption of a moderate amount of high-quality protein three times a day for healthy adult men and women with an average age of 36.9 provided a more effective means of stimulating 24-hour muscle protein synthesis than the common practice of skewing protein intake toward the evening meal.

Paddon-Jones and colleagues were now in the process of writing up a second NASA-funded study, splitting middle-aged, bed-rest patients between two groups: one supplemented with the amino acid leucine and one without. He said it seemed that leucine, a building block for protein, could have a “protective effect”​ against muscle loss, although the results of this experiment were yet to be published.

On/off, fine/finer ​

However, he said that Dutch research into protein supplementation of the elderly had shown that this was not so clear cut as its results​ revealed no significant reduction in muscle loss during short-term muscle disuse in those supplemented with 20g of protein twice a day. “But if you look at the population in the Netherlands, everybody rides bikes and dairy, and therefore protein, consumption is high. So these guys were already getting enough [protein].”​

“This isn’t a dimmer switch. If protein turns something on, you can’t turn that on more. If their intakes are already fine, you can’t make them finer.” ​

In this respect these findings could signal that leucine and protein assumptions applied only to populations where there was some kind of 'deficiency' or clinical need.

In a separate review​ by Paddon-Jones and Professor Heather Leidy from the University of Missouri, published in Current Opinion in Clinical Nutrition & Metabolic Care ​earlier this year, a protein threshold of around 30g per meal was suggested as a strategy and dietary framework for middle-aged and older adults concerned with maintaining muscle mass, while controlling body fat.

A message of moderation ​

Paddon-Jones said he was clear on one thing: a message of moderation was key, and a focus on meal intakes and activity important.

The results of his published study suggested the importance of protein distribution throughout the day, and he said that within this it was important to remind people not to neglect breakfast, something increasingly done in busy, modern society. 

He said he favoured a diet approach over supplementation, and added: “The trap some protein researchers fall into is to forget other important nutrients.” ​

However, supplementation could be a useful delivery method in certain situations, he said, where calorie intakes and appetite may be an issue, i.e. elderly and bed-bound patients. "I'm quite a fan of whey protein,"​ he said. 

Looking forward, the next area of focus would be to look at these nutrients in relation to the mitochondria, cells that play an important role in the generation of metabolic energy and linked to the ageing process, he said.