Metabolic rate, weight loss, and aging – practical applications


Metabolic rate and weight loss, what’s the connection? Did you notice how some people can eat anything they want and never gain weight? Maybe you had no problem with weight most of your life, but now it’s creeping up. It seems harder to lose weight now than when you were younger. 

One of the reasons for both of these “injustices” is your metabolic rate. It might be lower than other people’s. And on top of that, it starts slowing down after age 40. 

People put a lot of effort into increasing their metabolic rate to stay fit and healthy. However, an elevated metabolic rate is associated with faster aging and disease. The new insights into energy production help us understand that a faster metabolic rate is not better. You can certainly stay fit and healthy despite a slow metabolic rate.

What are metabolism and metabolic rate?

Metabolism is all the chemical reactions that create and break down energy. The rate at which your body burns calories is called the metabolic rate.

Metabolic rate is a sum of Resting Metabolic Rate (RMR), the thermic effect of meals, and Activity Energy Expenditure (daily activity + exercise). 

What factors affect the metabolic rate?

  1. Genetics affect your RMR.
  2. Body size and weight – bigger and heavier bodies burn more energy and have higher metabolic rates.
  3. Your activity level. The more active you are, the more fuel you burn. 
  4. Aging reduces our Resting Metabolic Rate and Activity Energy Expenditure.

Weight loss and metabolic rate

When we lose weight, our metabolic rate slows down. A smaller body requires less energy to function.

If you lose about 15 pounds, your average rate will decrease by about 100 Cal/day. About 83-80% of the weight reduction comes from losing fat. Only 17-20% of total weight loss comes from non-fat tissues, primarily muscle.

Contrary to common belief, it’s not the loss of muscle that slows down our metabolic rate but rather the loss of fat.

The more weight you lose, the slower your metabolic rate becomes, and the less food you need to provide your body with sufficient energy. And so when you transition to weight loss maintenance, your new “normal” food intake should be less than before you lost weight. Otherwise, you’ll start gaining weight back.

Theories of aging and metabolism

There are many theories of aging, but we’ll focus on three of the most widely accepted—all three base their concepts on our metabolism. 

The first is called the Rate Of Living and dates back to 1928. The author observed that all animals age similarly but at different rates. The faster the metabolic rate of an animal, the shorter its lifespan. Birds are the only exception that doesn’t fit the theory. They have a high metabolic rate and live longer than other animals with similar metabolism. 

A couple of decades later, the Free-Radical Theory came to life. It focuses on oxidative stress that damages our DNA and cells leading to disease and aging. 

Oxidative stress comes from free radicals, a byproduct of metabolism. Our life depends on energy production. Interestingly, the process itself creates free radicals that damage and age us. This theory explains well the bird exception but fails to explain the exercise paradox. 

We all intuitively know that physically active people live longer and healthier lives. However, they burn a lot more energy which produces more free radicals. So they are supposed to age faster!

A newer Mitochondrial Theory of aging takes the Free-Radical Theory further. It explains that free radicals are not just bad for us but carry out an essential role. What’s important from a health and aging standpoint is how efficiently the mitochondria produce energy. When the process is not efficient, too many free radicals leak out, and we age faster. Less fuel for the body produces fewer electrons to form free radicals. As a result, less damage to the cells and tissues and better functioning.

Practical applications

How can we apply this theoretical knowledge to ourselves and have longer and healthier lives? 

We know that age-related degenerative diseases don’t have to be a part of aging. And there is a lot we can do to slow the aging process down, at least in theory: 

1. Reduce food intake 

When you eat more calories than you can burn, there is an overabundance of electrons that leak and form damaging free radicals. Long-term caloric restriction animal studies show that animals live longer and stay “younger” longer. Age-related diseases like cancer, diabetes, dementia, and cardiovascular are delayed and even prevented. 

2. Move after a meal 

The most abundant energy supply and potential overflow of electrons happen after meals. If you move, go for a walk, clean up in the kitchen, etc., you use up those excess energy molecules resulting in fewer free radicals. It’s crucial to move after bigger meals.

3. Periodic or intermittent fasting

Many people find it easier to fast periodically than to restrict calories all the time. As a result, you can achieve caloric reduction over time. In The FastDiet, Dr. M. Mosley and M. Spencer introduce their practical approach to fasting, explain its benefits and share recipes.

In addition to caloric reduction, fasting encourages the production of ketone bodies with additional neuroprotective benefits. Low-carb or Keto diets are both fast-mimicking and have similar positive effects on longevity and healthy aging. 

References: – Energy Metabolism and the Burden of Multimorbidity in Older Adults: Results From the Baltimore Longitudinal Study of Aging – Metabolic Slowing and Reduced Oxidative Damage with Sustained Caloric Restriction Supports the Rate of Living and Oxidative Damage Theories of Aging – Caloric restriction and intermittent fasting: Two potential diets for successful brain aging

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