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Aging and Metabolism

Aging and Metabolism

Have you ever been told that the cause of your weight gain was aging? While it is true that your metabolism slows down as you age, it does not start slowing as early as you may think. 


First, what even is metabolism? Theterm metabolism refers to the process of turning food into energy. What we more commonly think of as metabolism is more accurately called metabolic rate or energy expenditure, which is the number of calories that your body uses and requires throughout the day.1


Your metabolism is able to provide your body with the energy it needs to simply function. Each person has a minimum amount of calories or energy that is needed to sustain life. This is what is known as your basal metabolic rate or BMR. 


When you are at rest, your body is still working behind the scenes and therefore still requires energy. Processes such as breathing, circulating blood, temperature regulation, digestion, and cell repair all require energy. 


Your metabolism rate depends on these factors:


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  • Basal metabolic rate (BMR): As we mentioned, when you are at rest, your body is still working. Therefore, BMR is the number of calories that your body requires while you are at rest. This would be your minimum requirement to keep you alive. This accounts for about 60-80% of your energy expenditure. 

  • Thermic effect of food (TEF): When we digest and absorb food it actually requires calories. TEF is the amount of energy required to digest and absorb your food! It accounts for about 10% of your energy expenditure. 

  • Exercise: For most people, the more understood part of your metabolism is probably the calories you burn through exercise. This can vary widely depending on how much the individual exercises.  

  • Non-exercise activity thermogenesis (NEAT): When you do activities outside of intentional exercise, they still add up! This includes things like standing, fidgeting, household chores, or other daily tasks. These activities are known as NEAT and vary widely among individuals. Both intentional exercise and NEAT account for around 20-40% of your energy expenditure.1


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Reasons why metabolic rate slows with age:


Now that you have an even deeper understanding of metabolism, you may now be understanding how someone's metabolic rate would decline with age. 


For starters, as you age muscle mass decreases. As we know, the more muscle mass a person has the more energy it takes to maintain it. Therefore, a reduced muscle mass would have a reduced energy expenditure. 


Additionally, as you age, exercise and day-to-day activity (NEAT) tends to decrease meaning that overall energy needs would also decrease. More research has shown us that a large part of the reduction in metabolic rate as you age is this decrease in overall activity level. 


Another aspect of the decline of the metabolic rate as you age is hormones. For females, as you age estrogen levels decrease. For males, testosterone levels decline. Both of which can affect your metabolic rate. Additionally, the metabolic rate can be affected by genetics, diseases, medications, weight, and diet history. While later in life than we once thought, the metabolism does slow down as part of the aging process. However, this has only a minor effect when compared to the reduction of activity and muscle mass. 


What to do:


If you do have a sense that your metabolic rate has declined, whether that is due to age or simply a lifestyle change, what can you do?


Whether your goal is to lose weight or maintain weight, you may find it more difficult after a change in lifestyle. If possible, resistance training can be a helpful way to maintain and build muscle mass, which in turn increases your energy expenditure.2 Whether you choose weight lifting, pilates, or another form of resistance training, find something you enjoy! 


Staying active as long as possible is also another helpful component of maintaining your metabolic rate. Whether that is incorporating more NEAT through daily activities such as standing or walking, aiming to reduce the amount of time you spend sitting can be helpful. 


Make sure to incorporate protein into your eating pattern. Ensuring you are getting adequate protein each day can help preserve the muscle mass you currently have and even support building muscle.3


While it is true that your metabolism declines as you age, research shows that this is largely due to the reduction in overall activity and muscle mass as you age and has less to do with age itself. 


Summary: Didn’t have time to read the whole article? Here’s what you need to know! Research has shown that the cause of a slowed metabolic rate is primarily due to reduced muscle mass and activity level that comes with age. By incorporating strength training, daily activity, and adequate protein intake, you can help delay the reduction of your metabolic rate. 


If you are interested to learn your personalized insights on how to eat right for your body’s needs, try out GenoPalate testing kit to make the best diet choices for your health as you age!



Resources:

  1. Manini T. M. (2010). Energy expenditure and aging.Aging research reviews,9(1), 1–11.https://doi.org/10.1016/j.arr.2009.08.002  

  2. Hunter GR, Wetzstein CJ, Fields DA, Brown A, Bamman MM. Resistance training increases total energy expenditure and free-living physical activity in older adults. J Appl Physiol (1985). 2000 Sep;89(3):977-84. doi: 10.1152/jappl.2000.89.3.977. PMID: 10956341. 

  3. Paddon-Jones D, Leidy H. Dietary protein and muscle in older persons.Curr Opin Clin Nutr Metab Care. 2014;17(1):5-11. doi:10.1097/MCO.0000000000000011

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Written by:

Frankie O'Brien, MS, RD, LDN

Registered Dietitian

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