“Metabolism is how your body takes stuff from the outside (food) and makes it part of your inside.”
This simple sentence, cheerily delivered by pediatric endocrinologist Robert Lustig MD in the first of a series of mini-videos on metabolic health, is the simplest explanation I’ve heard of the enormously complex process that drives every cell in your body.
“There are two parts to metabolism,” Lustig continues: “Burning and growth.”
Growth involves converting food components (amino acids, fatty acids, minerals, etc.) into bone, muscle, brain, kidney, liver, and virtually every other organ.
Burning is the process by which we turn food energy (generally from dietary carbohydrate or fat) into energy that fuels all our bodily processes. Cellular energy is called adenosine triphosphate (ATP) – more on this below.
Our bodies are made of trillions of cells. Each cell contains specialized structures called organelles that perform specific functions. Transforming calories into ATP occurs in organelles called mitochondria (they’re the little bean-shaped organisms pictured above; you’ve probably heard them described as “powerhouses of the cell”).
Each cell contains mitochondria; some have only a handful, others have hundreds of thousands. The brain has the largest number of mitochondria because it has to generate energy to power the transfer of information between neurons (neurotransmission) – the most energy-intensive process in the body.
When our brain cells aren’t able to generate enough energy, we feel tired, struggle to think clearly and experience memory problems. That’s why, even though your brain makes up only 2% of your body weight, it uses 20% of your energy. (Fun fact: chess grandmasters burn up to 6,000 calories a day while playing in a tournament, about as much as someone running two marathons!)
Why does metabolism matter?
Trillions of chemical reactions happen in your body every second, and all these reactions run on energy (ATP) generated by the mitochondria in your cells. Here’s a tiny snapshot of what’s going on in your cells right now, as you’re reading this article:
- Glucose consumption: As you read, your brain is actively processing information, which requires brain-cell energy. Your brain uses blood sugar (glucose) as its primary energy source; it is converted into ATP by a process called glycolysis.
- Oxygen Supply: Metabolism ensures a constant supply of oxygen to your brain cells through blood circulation. This oxygen is crucial for cognitive functions like concentration and comprehension.
- Blood flow regulation: Metabolic processes help regulate blood flow to the brain, ensuring it receives enough oxygen and nutrients to function efficiently.
- Neural Activity: Reading activates multiple areas of the brain involved in visual processing, language comprehension, and memory. Metabolism provides the energy required for these neurons to fire and communicate with each other.
- Staying alert & awake: Your metabolism helps maintain your overall energy levels. Even though reading is a sedentary activity, your brain remains active, and metabolic processes ensure you have the energy to stay awake and alert – even when reading something as dry as this article.
- Muscular activity: Eye muscles constantly move and adjust to focus on the text, facial muscles might engage for expressions, neck and shoulder muscles maintain head position, postural muscles keep you sitting or standing upright, and arm, hand and finger muscles are used to scroll through the text.
We can support — but not control — metabolic function
Why am I subjecting you to this excruciatingly detailed account of the metabolic processes in your brain and body? Because, as a nutritionist and health coach, my job is to help you eat and live in ways that support the proper functioning of your cells, with the ultimate aim of helping you lead a rich, fulfilling life.
Alas, many of us struggle with metabolic imbalance for reasons that are not fully within our control.
Genetic factors, for example, can impair metabolic functioning; these could include mutations in LEP (leptin deficiency), MC4R (appetite dysregulation), or LMNA (lipodystrophy) and cause severe metabolic dysfunction. Variants in the FTO gene (increased propensity to store fat) or TCF7L2 (diabetes susceptibility) amplify metabolic syndrome likelihood (more on this here and here). Meanwhile, mitochondrial defects causing impaired ATP production can disrupt energy homeostasis.
Social, environmental and psychological factors can also disrupt metabolic functioning; these include food insecurity, sedentary lifestyles (for instance, due to jobs that involve a lot of sitting and long periods of screen time), healthcare disparities (low-income populations often lack access to preventive care or genetic testing), weight stigma, weight cycling, adverse childhood experiences, post-traumatic stress disorder (PTSD), and more (see Part 3 of this series on metabolism).
Additional potential contributors to poor metabolic function include commonly prescribed medications (such as thiazide diuretics, beta blockers, immunosuppressants, corticosteroids, antipsychotics, antidepressants, and oral contraceptives), the natural aging process, and chronic conditions that exacerbate insulin resistance and inflammation, such as polycystic ovarian syndrome (PCOS) or sleep apnea.
So while metabolic function can be improved through multimodal strategies including nutrition, physical activity, sleep, stress management, and medications (ask your doctor), genetic predispositions and socioeconomic inequalities often limit efficacy. Addressing these barriers requires individualized approaches and systemic societal change.
One way to learn about nutrition, movement, and stress-management behaviors that support metabolic function is to join my online community, Savor, where we offer cook-along classes and recipes, in-person walks and online exercise classes, interviews with leading medical researchers, mindfulness & stress-management resources, and more.
Another is to work with me in one-on-one coaching. If you want to chat with me about how that might look, feel free to schedule a 30-minute discovery call by clicking on this link.