Does Your Metabolism Slow As You Age?

We decided to tackle this topic after a discussion I recently had that has happened many times before. I just finished giving a presentation about health and fitness. Afterwards I stick around to answer any questions people may have as they slowly filter out of the conference room. Several people commented to me that they know they need to start exercising now that they are getting older because their metabolism is slowing down and they are putting on weight. This is usually also accompanied by pointing to their midsection which they describe as rapidly expanding. So, in this episode of the podcast/newsletter we decided to take a look at whether or not your metabolic rate slows as you age.

We took a look at this study which analyzed total daily energy expenditure for over 6,000 people (males and females) aged newborn to 95 years old. It found that the amount of lean mass you have is a major contributor to the total daily energy expenditure (not surprisingly). When you equate for lean body mass, the metabolic rate of human beings stays the same from age 20 to age 60. So another way of saying this is that if your total daily energy expenditure is decreasing (burning less calories through the day), up until age 60 this is explained by the fact that you are losing lean body mass (muscle), not because your metabolism is fundamentally slowing.

After age 60, they did start to see metabolism slowing independent of lean mass. However, it was only about .7% per year. It was not a sudden, precipitous drop off. So by age 90, they did see a total daily energy expenditure decrease of about 25%. 

Another interesting finding of the study was that when you equate for lean body mass, the metabolic rate of men and women was the same. In other words, men tended to have a higher metabolic rate in absolute terms, but it is only because they tend to have more lean body mass.

Finally, we touched on this study which showed that obese subjects actually tend to have a higher metabolic rate than lean subjects. Again, this is explained by the fact that even though obese individuals are carrying extra body fat, they are also carrying more lean body mass as well.

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Simplified Takeaways…

1. When you equate for total lean body mass (muscle mass) your metabolic rate stays the same from age 20 to age 60.

2. So any decreases in metabolic rate prior to age 60 can be explained by lean mass (muscle) loss.

3. After age 60, metabolic rate decreased by about .7% per year.

4. When you equate for lean mass, the metabolic rate was the same between men and women. So men have a higher metabolic rate in absolute terms, but it is explained by having higher muscle mass.

5. Obese individuals tend to have a higher metabolic rate than lean individuals contrary to popular belief.

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