Why It's Time To Evolve From BMI & Improve True Markers Of Metabolic Health
When I say the word "flexible," what comes to mind? Perhaps your younger, more bendy self when you were a child? Or maybe a professional ballet dancer like Misty Copeland, who makes splits look ridiculously easy? I would venture to guess very few of you thought of metabolism or metabolic health.
In 2023, that's about to (and is already starting to) change, as the concept and personalized practice of metabolic flexibility and optimization are beginning to evolve and gain momentum.
Real quick, though, what is metabolism?
I'll spare you the ninth-grade biology lesson on the Krebs cycle, but suffice it to say, the biochemical process of cellular energy metabolism is majorly important. You see, our mitochondria are a metabolic hub where the nutrition we consume from foods and beverages is converted (i.e., calories are burned) into ATP energy. This ATP energy currency is then used up by the trillions of cells in our body to function all day, every day.
Cells make up tissues, which make up organs, which make up your body. I'm talking about your lungs taking deep breaths, heart pumping over a gallon of blood all through the body, gut digesting food and absorbing an array of nutrients, immune system mounting attacks against invading pathogens, neurons firing rapid signals throughout your nervous system, liver metabolizing and detoxifying countless compounds, muscles and ligaments holding us together and enabling us to move and be active, and so much more.
To say metabolism is absolutely fundamental to human biology and a healthful life would be an understatement.
If that's metabolism, then what is metabolic rate?
The all-important cellular metabolism process I described above is a close cousin to the concept of metabolic rate. This latter process is what people are alluding to when they say, "so-and-so [insert person's name] has a fast metabolism," in which we're saying a particular person appears to burn calories faster than other people do.
There are a couple of ways metabolic rate is described and measured:
- Basal metabolic rate (BMR): The number of calories you personally need to carry out basic bodily functions at rest.
- Resting metabolic rate (RMR), aka resting energy expenditure (REE): This is the actual number of calories you burn at rest.
Our REE makes up approximately 60 to 75% of the total calories that we burn daily (aka, our total energy expenditure, or TEE). That's a big piece of the overall energy balance equation, which is precisely why optimizing one's metabolic rate (a key way to flex your metabolic performance) can make a tangible difference, especially when it comes to energy balance and maintaining a healthy body composition.
Many factors can affect your metabolic rate, including genetics, biological sex1, aging2, mitochondrial health, muscle mass3, adiposity, insulin resistance, thyroid hormone health4, nutrition, meal timing, stress, sleep, physical activity, diseases, and more.
In addition to the calories you burn at rest, there are two other ways to burn calories: You can expend energy via any form of physical activity (any movement is good movement!) and dissipate energy through a process called thermogenesis, in which heat is produced.
Thermogenesis is a fascinating and important process that occurs in the gut (i.e., during the digestion of food), as well as in brown adipose tissue (BAT)5 and skeletal muscle. This metabolic process maintains our core body temperature in cold environments and transforms food calories into heat.
And then there's metabolic health.
Metabolism and metabolic rate are key features of metabolic health. What's more, metabolic health encompasses cardiometabolic health, an umbrella term that includes critical processes of blood glucose, lipid, and blood pressure regulation, as well as inflammatory balance.
Taking a holistic approach, I think of "metabolic health" as the mother ship term encompassing all of the above concepts.
Interestingly (and a common misconception), metabolism doesn't slow down in older age as much as once thought, nor are those changes inevitable! Furthermore, the concept that dysfunction or perturbation in metabolic health are expected or "normal" with aging is false.
Cate Shanahan, M.D., medical director of ABC Metabolic Health Center and bestselling author of Deep Nutrition and The FATBURN Fix, explains puts it this way: "Your metabolism isn’t slowing down, it’s breaking down."
We have more "skin" in the metabolic health game than we give ourselves credit for (and that's empowering). The fact is, it's critical to nurture and optimize our metabolism and metabolic health throughout life by taking proactive steps to maintain and optimize key organs, biomarkers, and related metrics (more on those below).
The situation: We are metabolically unhealthy in epidemic proportions.
If the U.S. got a metabolic health report card, it would be failing. Indeed, when considering blood sugar, lipids, and inflammation (the trifecta of cardiometabolic health status)—a shocking seven out eight Americans are metabolically unhealthy.
According to nationally representative data, almost three-quarters (73%), of U.S. adults have a BMI that meets criteria for overweight or obesity6. Additionally, over 11% of the U.S. population suffers from diabetes7, while another one-third of U.S. adults have prediabetes8 (which if not reversed, will often progress to full-blown diabetes).
Furthermore, half of American adults have high blood pressure (aka high blood pressure9)—that's over 100 million people. Lipid dysregulation (i.e., dyslipidemia) runs rampant, too. Nearly 40% of adults have high total cholesterol10.
Within this epidemic, socioeconomic inequities are evident, with BIPOC communities affected disproportionately by metabolic health concerns. What's more, even our youth are suffering from metabolic dysfunction and its many comorbid consequences. Over 20% of children and adolescents ages 6 and older have obesity11, and 7% of children already have high cholesterol12.
Even our country's health care providers are suffering metabolically. Kien Vuu, M.D., and bestselling author of Thrive State: Your Blueprint for Optimal Health, Longevity, and Peak Performance, candidly shares that: "Before I was a doctor specializing in performance medicine and helping clients leverage pivotal wellness strategies like targeted nutrition, I was a doctor personally struggling with excess weight and suffering with cardiometabolic health dysfunction (all before the age of 40)."
He goes on to say that he doesn't regret the journey because he knows firsthand "how crucial metabolic health is for my whole-body health and longevity. And I get to empower and equip people striving for holistic health."
Thankfully, metabolism and metabolic health are malleable.
Let's revisit my earlier ballet metaphor. How do Misty Copeland or my fellow arts boarding school grad Whitney Huell and other talented dancers make flexibility look effortless? Answer: effort. (Lots of it, over many years). Splits aren't actually easy, and neither is balancing and doing complex maneuvers on pointe shoes. Those skills require proactive, routine stretching and practice, plus a personalized approach for long-term maintenance.
Similarly, nurturing and optimizing metabolic health over a lifetime takes real intention and action. The awesome fact is that metabolism and metabolic health are malleable. Unlike your stature or eye color, you have the ability to affect and even pivot your metabolic destiny (and thus, overall health and longevity).
In 2023 and beyond, we'll take active and personalized steps to improve metabolic flexibility and performance. But first, we'll need to evolve from BMI and move toward true markers of metabolic health.
Markers of metabolic health — is BMI the best metric? (Spoiler alert: nope.)
Body mass index (BMI) considers height and weight to grossly estimate one's weight/adiposity status13 (i.e., underweight, healthy, overweight, obesity). While useful in certain clinical settings and for broad data sets in epidemiologic (population-level) research, BMI is not as useful at the individual level if your goal is a comprehensive and personalized approach to optimize metabolic health.
BMI is insensitive to body composition nuance (e.g., a muscular and highly fit athlete may register in the "overweight" or "obese" categories), gender, and racial uniqueness. As mbg Collective member and the father of functional medicine Jeffrey Bland, Ph.D., previously shared with mbg: "The BMI standard was developed for an idealized Caucasian male, and the thresholds remain rather oblivious to important discrepancies warranted by gender and ethnicity."
Also, weight is an incredibly narrow view of metabolic health. Functional medicine nutritionist Brooke Scheller, DCN, CNS, explains, "Metabolism isn't just about weight. It actually has more to do with how our body uses the food we eat and converts it to fuel for energy."
"It's hurtful to reduce personal health to a number that takes no account of your behaviors and the socioeconomic pressures that play major roles in so many people's lives," Bland shares. And registered dietitian and intuitive eating counselor Courtney Vickery, M.S., R.D., L.D., astutely points out that "weight can fluctuate for many reasons, such as hormones, water retention, and muscular growth."
Indeed, metabolism and metabolic health are so much more than a number on a scale. After all, it's almost 2023; thus, it's time to graduate, evolving from an antiquated and oversimplified view of weight (i.e., energy in, energy out) and related metrics (BMI).
As Shanahan explains, "The key to losing weight is recognizing that it's not a problem of willpower but of metabolic breakdown. You can fix your metabolism."
Truly useful metabolic health metrics and how to optimize them.
To get you started, here is a list of useful metabolic health metrics—from waist circumference and blood pressure to glucose, lipids, and much more—to know, track with intention, and optimize with the support of your health care partner in the year ahead.
Keep an eye on these in the name of metabolic health, beyond BMI:
- Body composition: This can be measured through weight but also waist circumference, fit of clothing, with the help of a smart scale (e.g., WITHINGS BODY+), calipers, bioelectrical impedance, BodPod (mostly used in clinical and research settings), hand grip strength, dual X-ray absorptiometry (DXA, mostly used in clinical and research settings), and peripheral quantitative computed tomography (pQCT, almost exclusively used in research settings and focused on bone health).
- Metabolic rate: This can be measured through indirect calorimetry in a laboratory setting, BMR/RMR estimates via calculators (research indicates that the Harris-Benedict equation is more accurate for individuals, while the Mifflin-St. Jeor equation is better for groups), and a carbon dioxide measurement like this Lumen tool.
- Key cardiometabolic health biomarkers: This can be measured through blood pressure, fasting blood glucose, an oral glucose tolerance test, continuous glucose monitoring (e.g., with a cutting-edge CGM like Levels), fasting insulin, HOMA-IR, longer-term glycemic control/blood sugar balance (hemoglobin A1C, HbA1c), blood lipids (triglycerides, total cholesterol, LDL cholesterol, HDL cholesterol, TG:HDL ratio), alanine aminotransferase (ALT), uric acid, inflammatory and stress status via high-sensitivity C-reactive protein (hs-CRP), cortisol, and erythrocyte sedimentation rate (ESR). See healthy ranges to aim for here.
- Nutritional status: This can be measured through protein sufficiency and key blood biomarkers such as B6, B12, iron (serum ferritin, transferrin, hemoglobin, hematocrit), serum ascorbic acid (vitamin C), magnesium red blood cell (RBC) test, serum total 25-hydroxyvitamin D (i.e., 25(OH)D for vitamin D status), and omega-3 index for omega-3 status (with basic and comprehensive testing panel options available). Note: Protein needs can vary significantly with life stage, activity level, and health status, but baseline needs are approximately 1.0 to 1.6 grams of protein per kilogram of body weight per day.
- Hormone balance: This can be measured through a comprehensive thyroid panel (TSH, T3, reverse T3, T4, thyroid antibodies), sex hormones (estradiol, testosterone, progesterone, etc.), adrenal hormones (cortisol, DHEA).
Put it into practice:
Takeaway of the trend.
The science is clear: We have many strategies and tools to help flex our metabolism and actively defy metabolic age expectations throughout life. I remain hopeful that we can begin to turn the tide on metabolic health in our nation before it's too late, and so do many others working in this field.
I'll leave you with the thrilling vision for a metabolic future that Deshanie Rai, Ph.D., FACN, vice president of global scientific and regulatory affairs at OmniActive Health Technologies shares: "I am excited about how fast the science of personalized metabolic health is advancing in the pursuit of optimal health goals at the individual level. We are no longer just focusing on phenotypes and genotypes when it comes to metabolism. The field is rapidly evolving to understand their integration with epigenetics, nutrigenetics, and metabolomics (including the microbiome), which collectively can help optimize more personalized nutrition approaches to tackle metabolic imbalances."
Ashley Jordan Ferira, Ph.D., RDN is Vice President of Scientific Affairs at mindbodygreen. Ashley received her B.A. in Biological Basis of Behavior from the University of Pennsylvania (along with a double minor in Nutrition and Music) and Ph.D. in Foods and Nutrition from the University of Georgia. Her research contributions span vitamin D, cardiometabolic health, bone density, and weight management. Ferira is a nutrition scientist and dietitian with experience in nutrition product innovation and development, scientific affairs, education, communications, and SEO writing for global firms, including Nature Made, Metagenics, Three Ships, and mindbodygreen.
In addition to her mindbodygreen contributions, Ferira is published in Health, Metagenics Institute, American Family Physician, The Journal of Clinical Endocrinology & Metabolism, and Osteoporosis International. She has a passion for the translation of evidence-based science into innovative and high-quality products and information that help people lead healthier lives. She is a believer in compassionate, informed, and personalized approaches to nutrition, health care, and wellness. Ashley lives in beautiful Charleston, South Carolina, where she was born and raised. Whether savoring an orchestral performance or delectable meal at a local restaurant, you will find her enjoying Charleston’s cultural and culinary arts with family and friends.