Leucine As we age we lose muscle mass. How and why the process of aging causes muscles to break down scientists still don’t know, but perhaps they do now know how to stop the process. All you have to do is make sure you get enough leucine by eating protein-rich foods every day. According to the Australian nutritionist Cameron Keith McDonald, a daily dose of 7.12 g leucine is enough to halt age-related muscle loss.
McDonald, who works at the University of Queensland, analysed data on 368 Danes aged between 35 and 65. The Danes had taken part in a study on cardiovascular disease, and had been monitored for six years at some point. Before the study started and at the end the researchers had measured the participants’ body composition. In addition, they knew whether the participants exercised, and how much protein and leucine they consumed.
Among the participants who were younger than 65, McDonald found no correlations, but among the over 65s there were some. The over 65s lost more lean body mass [i.e. muscle mass] the less leucine there was in their diet. In the group of over 65s with the highest leucine intake the muscle mass loss was nil.
In the figure below the researchers have filtered out as many other factors as possible, such as baseline lean body mass, sex, age, energy intake and physical activity.
To make sure you consume 7.12 g leucine every day you need to eat about 1.25 g protein per kg bodyweight, McDonald calculated. If you consume this amount, and spread your protein intake over three meals a day, then you’ll consume about 2.5 g leucine per meal.
And that’s exactly the minimum amount of leucine that is capable of stimulating muscle growth.
Lean body mass change over 6 years is associated with dietary leucine intake in an older Danish population
Higher protein intake, and particularly higher leucine intake, is associated with attenuated loss of lean body mass (LBM) over time in older individuals. Dietary leucine is thought to be a key mediator of anabolism. This study aimed to assess this relationship over 6 years among younger and older adult Danes. Dietary leucine intake was assessed at baseline and after 6 years in men and women, aged 35–65 years, participating in the Danish cohort of the WHO-MONICA (Multinational MONItoring of trends and determinants in CArdiovascular disease) study (n 368). Changes in LBM over the 6 years were measured by bioelectrical impedance using equations developed for this Danish population. The association between leucine and LBM changes was examined using multivariate linear regression and ANCOVA analyses adjusted for potential confounders. After adjustment for baseline LBM, sex, age, energy intake and physical activity, leucine intake was associated with LBM change in those older than 65 years (n 79), with no effect seen in those younger than 65 years. Older participants in the highest quartile of leucine intake (7·1 g/d) experienced LBM maintenance, whereas lower intakes were associated with LBM loss over 6 years (for trend: ?=0·434, P=0·03). Sensitivity analysis indicated no effect modification of sex or the presence of CVD. Greater leucine intake in conjunction with adequate total protein intake was associated with long-term LBM retention in a healthy older Danish population. This study corroborates findings from laboratory investigations in relation to protein and leucine intakes and LBM change. A more diverse and larger sample is needed for confirmation of these results.