Is It Possible to Change a Slow Metabolism?

Many patients with obesity blame weight gain on their metabolism. The reality is that metabolism can be blamed for weight regain after people try to lose weight! As we age, our metabolism does slow down; sometimes we think it stops working.

Caroline Apovian, MD

Metabolism, or resting energy expenditure, is directly related to how much muscle mass we have. As we age, we lose muscle, which is called sarcopenia.

What happens to our metabolism when we try to lose weight? Let's first discuss what metabolism is.

What Is Metabolism?

Metabolism refers to the chemical reactions in the body's cells that convert food into energy for sustaining life, cellular processes, and as storage for a rainy day.

Total energy expenditure (TEE) is broken down into resting energy expenditure (REE), thermic effect of food (TEF), and nonresting expenditure (NREE) or physical activity, and is made up of:

TEE = 60% REE + 10% TEF + 30% NREE

An elegant study performed by Dr Rudy Leibel explored the effects of weight loss or weight gain on metabolism in 23 lean and 18 patients with obesity who were placed in a metabolic chamber. Weight loss of 10% or 20% body weight led to a decrease in TEE roughly equal to about 300 kcal/d, and an increase in body weight of 10% caused an increase in TEE of about 500 kcal/d. These changes led to the patient reverting to the prior weight (before weight loss or gain). In other words, Dr Leibel postulated a feedback mechanism for the effect of fat mass decrease or increase on energy metabolism. The feedback mechanism or signal from fat was subsequently found to be leptin.

In a later study, Leibel and colleagues investigated the effects of body fat mass change on TEE and found that a 10% reduction in weight caused a decrease of TEE by 21%, comprising a decrease in NREE of 37.5% and a decrease in REE of 11.6%.

Therefore, the biggest change in TEE comes from NREE or exercise energy expenditure. The 35% variance in NEE change was accounted for by a decrease in muscle work efficiency in generating 10 watts or low levels of work such as walking.

In other words, when persons with obesity or lean persons lose weight, the efficiency of muscle at low levels of work increases such that one burns less energy when walking than one normally would. This helps conserve energy and tends to cause the body to go back to the higher weight.

So, How Can One Change Metabolism?

Let's say one did lose weight and wants to counteract this TEE loss and increased muscle efficiency at low levels of work.

To counteract this effect, one should increase muscle work beyond low level so that more energy is expended. Another way would be to increase muscle mass so that there is more muscle that can do work.

This is exactly how metabolism can be altered or increased. What can be changed most readily, and what we have the most power over in our bodies, is the NREE.

To do this, muscles need anabolic power — the power to heal and build muscle mass. Anabolic power comes from eating healthy protein sources such as lean chicken, fish, beef, and eggs as well as dry beans, tofu, and dairy products.. It seems that older adults (> 60 years) need more protein than younger adults to build muscle mass, due to the body's natural aging process which leads to sarcopenia. How much more? Studies show between 1.2 and 1.5 g/kg of body weight per day, whereas younger persons need 0.80 g/kg.

Developing sarcopenia with age involves muscle losing the ability to use protein and amino acids to rebuild injured tissue.

Let's put this in perspective for treating obesity.

Obesity is brought on by the body's defense of a higher body weight by interaction with the environment of highly processed foods that work on the reward pathway, leading to weight gain and resistance to satiety. Weight loss via diet, exercise, and medications works, but this weight loss is also accompanied by a decrease in TEE.

Weight loss is primarily fat mass loss, but depending on the degree of protein intake and muscle resistance training, 20%-50% of the total weight loss is muscle mass loss. Therefore, higher-protein diets and resistance exercise can be useful in preserving muscle mass and counteracting the decrease in TEE, maintaining energy expenditure. In older patients, an additional factor is the muscle's lack of ability to use protein as an anabolic agent to protect muscle mass and thus the need for higher protein loads to do this.

All in all, can doctors help patients boost their metabolism, especially as they lose weight and maintain that loss? Yes — through protein intake and resistance exercise training.

Here are some tips to help your patients get cardio and resistance exercise into their routine.

First find out whether your patient prefers a social exercise interaction or solo training. If social, then the gym or classes such as cycling or boot camps at those gyms may work for them, especially if they can go with a friend. If solo is better, than a gym in the home might work. Peloton bikes are expensive but the interaction is all on the website!
A personal trainer may help motivate the patient if they know someone is waiting for them.

Let's hit the gym!

Another note: There are agents in the obesity treatment pipeline that purport to change body composition while helping patients lose weight. Some of these agents are myostatin antagonists and antibodies that inhibit the activity of myostatin to break down muscle. These agents have been found to build muscle mass, but whether the quality of the muscle mass leads to an increase in muscle strength or functionality remains controversial. The next frontier in obesity treatment will be about decreasing fat mass and increasing muscle mass while making sure that increased muscle mass leads to improved functionality.

In the meantime, aside from new agents on the horizon, the best and healthiest way to keep metabolism on the up and up is to eat healthy lean proteins and exercise. How much exercise? The recommendation is 30-60 minutes of moderate to vigorous physical activity at least 5 days per week; plus 20 minutes of resistance exercise training 2-3 days per week for upper- and lower-extremity and core strength.

Again, let's hit the gym!

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