A 2021 study conducted by Herman Pontzer might redefine the way we think of metabolism. We've all heard the old assumption that thin people have a fast metabolism and heavier people have a slow metabolism, but is this true?
Studies show that only 1 in 8 Americans, even those of normal weight, have optimal metabolic health. This article aims to demystify metabolism and explain how appropriate lab testing can help you understand it clearly.
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What is Metabolism?
Metabolism is the complex sum of all biochemical processes occurring within an organism to sustain life. We typically think of the thyroid driving metabolism, but that's only one part of a complex metabolic ecosystem.
Study Findings and Implications in Weight Management
Luckily, while Pontzer's study might change our thinking on metabolism, its findings were simple. The study authors enrolled 6,421 people from ages 8 days to 95 years, accounting for a wide range of factors, including lean mass, fat mass, and even pregnancy.
Age
Age was the main factor in metabolic rate—not year by year, though. Instead, the study found metabolic rate tied to 4 separate age groups:
- Fastest: Neonate to 1 year
- Declines Slowly: 1-20 years
- Remains Stable: 20-60 years (even during pregnancy)
- Declines Slowly: 60+ years
It makes sense that metabolism would be fastest in a newborn because major developments need to happen rapidly. We also grow rapidly from ages 1 to 20, including puberty, with a brief spike in growth hormone and sex hormones in our teenage years.
Beyond age, they accounted for lean and fat mass and how these affect metabolism.
Body Composition
The study found that having more body fat was directly related to lowered metabolism. This finding challenges the belief that people with a slower metabolism gain more fat. Instead, the study suggests that the addition of fat mass causes the metabolism to slow down, not the other way around, as many people assume.
So, what option is left to keep our metabolism at its peak? Since aging is out of our control, the focus shifts to lowering fat mass while maintaining lean mass.
Other Considerations
There are several other considerations related to metabolic rate, including:
- Appetite level
- The balance between food absorption and elimination
- Weight distribution (e.g., belly fat versus fat in other areas)
- Variations in energy levels despite similar calorie intake
Can medical weight management go beyond calories in versus calories out to give patients more hope? Luckily, the answer is a resounding yes!
Factors Impacting Metabolism
Many underlying factors cause slower metabolism, weight gain, and decreased energy as we age.
Insulin Resistance
Insulin resistance is arguably the most universal driver of increased weight gain today. The typical diet in modern society entails ultra-processed sugars and starch-based foods. While this seems less impactful while we're young, it catches up to us increasingly with age.
When blood sugar rises, insulin levels increase to drive sugar into our cells. Problems occur when blood sugar is too high, too often, eventually leading to insulin resistance, even in those who aren't officially diabetic.
Insulin resistance can slow metabolism by:
- Increasing fat synthesis from elevated blood sugar
- Increasing fat storage
- Decreasing lipolysis, or the burning of fat for energy
- Increasing appetite and caloric intake
Lab assessment for insulin resistance is similar to tests for diabetes, including markers like fasting blood glucose, fasting insulin, and hemoglobin A1c (HbA1c). HbA1c provides insights into average blood glucose levels over several months while fasting blood glucose and insulin levels offer only the level at the time of the blood draw.
Vitamin D testing is also critical. Vitamin D, also a hormone, impacts insulin sensitivity, fat tissue regulation, energy metabolism, and inflammation regulation, which in turn impacts fat metabolism. Notably, normal lab ranges don't necessarily indicate optimal levels.
Testing provides valuable insights into practical strategies for confirming and treating insulin resistance, boosting metabolism, and improving weight management. Improving insulin sensitivity also directly addresses fluctuations in energy and mood related to blood sugar dysregulation.
Stress Hormones
Chronic stress is a significant issue in society today. It can lead to adrenal dysfunction, the suboptimal functioning of your internal stress management system, resulting in elevated cortisol, low cortisol, or low dehydroepiandrosterone (DHEA).
High cortisol levels increase blood sugar levels, worsening insulin resistance and metabolic health over time. Chronically elevated cortisol levels are often accompanied by low DHEA-sulfate levels.
DHEA is cortisol's counterpart for stress management. Low DHEA can lead to lower levels of sex hormones, further impacting metabolism.
Salivary adrenal labs help assess the body's ability to manage stress and its effects on metabolism and weight.
Thyroid Hormones
Adrenal dysfunction can also impact thyroid function in several ways. Cells become less receptive to the metabolism-stimulating effects of the thyroid hormone, and the ability of thyroid hormone to metabolize from T4 to active T3 becomes impaired.
Thyroid hormones are typically the first area evaluated when addressing issues related to weight and fatigue, as inadequate levels often make it more difficult for patients to manage these conditions. Thyroid hormones directly influence metabolic rate, fat and glucose metabolism, and weight regulation.
Crucial thyroid labs include thyroid stimulating hormone (TSH), thyroxine (T4), free T4, triiodothyronine (T3), free T3, reverse T3, and thyroid antibodies.
While replacing thyroid hormone is often the first consideration, it is essential to remember that adrenal dysfunction can significantly impact thyroid function upstream. Additionally, if antibodies are elevated, addressing the underlying causes of autoimmune activation is crucial.
Sex Hormones
Sex hormones, such as estradiol, progesterone, and testosterone, control hundreds of processes in the body and significantly impact metabolism and weight.
High estrogen levels, or estrogen dominance in relation to progesterone, can lead to increased fat storage and other adverse health effects.
Inadequate testosterone levels can impair the body's ability to maintain optimal muscle mass and tone, leading to lower metabolic rate and impaired recovery.
It's important to note that low or high sex hormone levels can cause various impairments in metabolism, so optimal levels are critical.
Microbiome Diversity
The microbiome has a complex metabolism of its own that affects how we break down and absorb food and how our immune system reacts to the foods we eat.
Studies have shown that fitter people, particularly high-level athletes, tend to have a more diverse gut microbiome than obese and insulin-resistant individuals. The diversity and composition of the microbiome have a considerable impact on metabolism and weight management.
Gut testing can help identify underlying factors and guide targeted, more effective medical weight management and wellness strategies.
Functional Testing for Root Cause Identification
Functional testing offers an effective way to get to the root cause of weight gain and metabolic issues beyond calories in versus calories out.
Micronutrient Testing
White blood cell (WBC) micronutrient testing offers deeper insights into nutritional status than typical blood serum testing alone. While a blood serum test shows a snapshot in time, WBC micronutrient testing provides a superior long-term picture of bodily stores. Think of it like hemoglobin A1c compared to fasting blood glucose.
This test includes vitamins, minerals, and fatty acids. Typical diets often have imbalanced omega ratios, which cause chronic inflammation and impair fat metabolism. Micronutrient testing can provide insights for targeted nutritional strategies.
Genetic Metabolism Testing
Not everyone metabolizes nutrients the same way. Some people have impaired metabolism and chronic fatigue related to altered gene makeup.
A common example is a homozygous MTHFR gene mutation. It impairs the metabolism of cobalamin (B12), folate (B9), and pyridoxine (B6) into their active forms. All 3 of these vitamins are critical to cellular energy production from fats, carbohydrates, and protein. For this reason, accounting for gene mutations is essential to restoring optimal metabolism.
Heavy Metal Testing
Heavy metals such as lead, mercury, and arsenic don't have to be at acute levels to cause significant metabolic problems. They are present throughout our environment, including foods, household products, the water supply, dental fillings, and other sources.
Studies have shown that various heavy metals directly impair metabolism and increase fat storage. Heavy metals can affect metabolism through various mechanisms:
- Metabolic enzyme disruption
- Impairing mitochondrial function (mitochondria make useable energy from food)
- Impairing nutrient absorption
- Increasing oxidative stress and cellular damage
- Disrupting hormone regulation
- Increasing fat storage and inflammation
- Impairing fat metabolism
Typical medical testing will miss the heavy metals stored away in the body, but appropriate heavy metal testing protocols can reveal levels contributing to metabolic issues.
Here are some popular heavy metal testing options offered by Rupa Health:
- Hair Elements by Doctor's Data
- Elemental Analysis by Genova Diagnostics
- Metals - Toxic + Nutrient Elements - Red Blood Cell by Mosaic Diagnostics (formerly Great Plains)
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Key Takeaways
- This breakthrough study on metabolism provides new insights while making us reconsider older assumptions.
- Several factors can impact metabolism, including age, stress, genetics, hormones, environmental favors, and more.
- While calories in versus calories out is still a foundational component of weight management, medical lab testing can provide more targeted, root-cause-centered strategies for effective medical weight management and optimal metabolism.
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