Nutritiously Happy

Does our metabolism slow down as we get older?  For the answer to this question and others, or to ask your own nutrition-related question, please visit my new blog Dishin’ Dietitian!

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A study in the American Journal of Physiology, Endocrinology and Metabolism compared the resting metabolic rate (RMR) of physically active men, comparing ‘young’ (19-36 years old) subjects and ‘older’ (52-75 years old) subjects to determine whether metabolism decreased with age.  The subjects’ exercise volume (number of hours per week) and caloric intake were recorded.

Researchers originally focused on fat free mass, such as muscle and lean body tissue, calling it the “primary determinant of the age-related decline in RMR.”  Humans tend to lose muscle and lean body mass as part of the aging process.  Muscle and lean body mass are highly active tissues, requiring calories for energy.  Not surprisingly, reduced lean body mass leads to less calorie burn.  Over time, less calorie burn can lead to weight gain.   

Then researchers wondered, ‘Will metabolism still slow down if older adults maintain their exercise and caloric intake?’ 

Van Pelt et al. found that, when weekly exercise volume was matched between young and older adults, there was no significant difference between the groups’ resting metabolic rates.  Thus, when the older adults exercised as much as their younger counterparts, they achieved the same metabolic rate.  This implies that the dreaded age-related slowing of metabolism is actually more related to a decline in the amount of exercise as we age.

Researchers also studied the relationship between resting metabolic rate and caloric intake.  Older men exhibited less energy intake, which decreases the body’s metabolic rate, when compared to younger men.  However, when matched for daily caloric intake, there was again no significant difference in metabolism between the two age groups. 

Overall, the data shows reduced RMR in older men, even if those subjects remained physically active.  However, this is largely explained by two factors – a decreased amount of time spent on exercise and lesser caloric intake – both of which are common in aging.  Among men who performed the same volume of endurance exercise and consumed equal calories per day, metabolic rate was indistinguishable.  These findings are similar to a previous study by the same authors, who concluded that there was no age-related difference in the metabolic rate of young and older women when exercise and caloric intake were equal.

Moral of the Story: Don’t let aging and a ‘slowing metabolism’ serve as an excuse to staying healthy.  Stay active and let good health be one of your lifelong priorities.