Does Dieting Ruin Metabolism?

A topic that comes up a lot with clients in our sessions is a fear that because of past food restriction or dieting that they have ruined their metabolism for good. Fortunately, metabolism isn’t a thing that can be destroyed. This is one of the most common misconceptions I hear, and it stems from a general misunderstanding of what metabolism is and how it works. 

To say it simply, metabolism is the word we use to describe all of the complex chemical processes that take place as we convert food into energy. If metabolism was broken, there would be no energy. I always like to tell my clients though that in every nutrition myth there is a grain of truth somewhere that can help us to have a better understanding of where the myth came from. So where is the truth in this myth?

The part of this idea that is true is that metabolism changes greatly depending on how much energy is being consumed and how much is being used. I often find myself contrasting human metabolism with how a car works. In a car, we can fairly accurately calculate how many miles per gallon the car will consume under a given set of circumstances. If we change one of those circumstances like driving faster, pulling a trailer, changing the tires, etc, the efficiency of the car will also change. This is also true with human metabolism. If you change your circumstances like starting to exercise more or exercising too much or taking a new medication, the rate you metabolize food can change. Most people already understand this. Where human bodies and cars are so different is that bodies can adapt to changes in the amount of energy available. 

When I was in high school, I regularly bought just enough gas to get me to school or my next destination with change scrounged out of my bag. I rarely had enough money to completely fill my tank. But this didn’t change how efficient my car was. If I ran out of gas my car stopped running (and I learned an important lesson). But our bodies are so much smarter and more sophisticated than our cars. Our bodies can decrease how much energy they need when there isn’t enough available by slowing down certain processes. They can also adjust how much food they are absorbing by slowing digestion in order to soak up as much energy as possible from the little that is available. If our cars were able to adapt like our bodies do, we might expect that if we didn’t fill up the tank every time the radio wouldn’t work or the windows wouldn’t roll down or maybe the car would still go but it just wouldn’t ever get above 30 miles per hour.

So, what many have come to believe is destruction of metabolism is actually the body being really smart and adapting to the environment that is available. This makes sense considering our bodies are designed to survive even when food is scarce. The question for many remains whether those changes to metabolism are permanent. Just like metabolism changes when energy is limited, it can resume its normal cadence when energy is available. Food digests at a faster rate, and we can think more clearly, regulate our emotions more easily, and have the energy to go through our daily tasks with greater ease. 

Of course, the answer is never as simple as ‘do this one thing and everything will be just the way it was.’ There are some changes or shifts that do tend to stick around. Bodies don’t like weight cycling that often comes with dieting, and this may lead the body to adapt metabolic processes in order to maintain a more stable weight. Science also shows that metabolism slows as a normal part of aging. 

As with most ideas we talk about on this blog, it’s a complicated picture and this just scrapes the surface. If you are interested in exploring with someone on our team, you can make an appointment on our website by clicking this link.

References:

Doucet E, et al. Evidence for the existence of adaptive thermogenesis during weight loss. Br J Nutr. 2001 Jun;85(6):715-23.

Leibel RL, et al. Changes in energy expenditure resulting from altered body weight. N Engl J Med. 1995 Mar 9;332(10):621-8.

Rosenbaum M, and Leibel R. Adaptive thermogenesis in humans. Int J Obes (Lond). 2010 Oct; 34(1): S47–S55.