🩺 Ask Dr. Cruz
Edition # 3 | November 2025
Question: What is metabolic flexibility?
➡️ ANSWER: Metabolic flexibility is your body’s ability to switch efficiently between burning carbohydrates and burning fat, depending on what your body needs in the moment.
Why Metabolic Flexibility Matters for Cardiovascular Health
Metabolic health and cardiovascular health are inseparable. The heart is one of the most metabolically active organs in the body and depends on the ability to use different fuel sources efficiently — especially fatty acids. Here are 5 reasons why metabolic flexibility matters:
1. Reduced metabolic flexibility increases cardiovascular risk
When the body cannot switch efficiently between fuels, you see:
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Elevated glucose and insulin
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Higher visceral fat
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Increased inflammation (hs-CRP)
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Impaired mitochondrial function
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Higher triglycerides and LDL-particle number
These changes accelerate atherosclerosis, endothelial dysfunction, and cardiometabolic disease.
📚 Key evidence:
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Metabolic inflexibility is strongly associated with insulin resistance and cardiometabolic disease (Goodpaster & Sparks, Cell Metabolism, 2017).
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Loss of metabolic flexibility predicts future cardiovascular events independent of BMI (Smith et al., J Clin Endocrinol Metab, 2020).
2. Your mitochondria power the heart — and metabolic flexibility protects them
The heart requires enormous energy production. Mitochondria must constantly adapt to fuel availability.
Poor metabolic flexibility causes:
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Higher oxidative stress
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Reduced ATP production
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Mitochondrial overload and inflammation
All of which lead to reduced exercise capacity, fatigue, and long-term cardiovascular decline.
📚 Evidence:
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Impaired metabolic switching reduces mitochondrial efficiency and increases oxidative stress in cardiac tissue (Stanley et al., Circulation Research, 2005).
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Mitochondrial dysfunction and metabolic rigidity are early drivers of heart failure (Lopaschuk & Karwi, Circulation Research, 2020).
3. Metabolic flexibility directly affects blood pressure, HRV, and autonomic balance
Patients with poor metabolic flexibility commonly experience:
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Lower HRV
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Higher resting heart rate
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Increased sympathetic tone
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Sleep disruption
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Impaired recovery from exercise or stress
This makes the cardiovascular system more reactive and less resilient.
📚 Evidence:
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Metabolic impairment is linked to reduced HRV and increased sympathetic activity (Thayer & Lane, Neurosci Biobehav Rev, 2009).
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Circadian misalignment and inflexibility increase cardiometabolic risk (Scheer et al., PNAS, 2009).
4. Metabolic flexibility improves exercise efficiency and fitness
Your VO₂ max, fat oxidation curve, and training response depend heavily on the ability to shift between carb and fat metabolism.
Better metabolic flexibility leads to:
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Improved endurance
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Lower lactate production
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Higher fat-burning at rest
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Improved recovery
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Greater cardiovascular efficiency
📚 Evidence:
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Flexible substrate utilization is associated with improved exercise economy and cardiac output (Helge et al., J Physiol, 2007).
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Enhancing metabolic flexibility improves fitness and insulin sensitivity (Kelly & Goodpaster, Exercise and Sport Sciences Reviews, 2023).
🩺 Ask Dr. Cruz
Edition # 2 | October 2025
“I’m 30 with normal cholesterol and blood pressure — so why do I already have plaque in my coronary arteries?”
➡️ ANSWER: Inflammation
Inflammation & Atherosclerosis
In this patient’s case, UC wasn’t just affecting the gut — it was fueling systemic inflammation that can involve the arteries and accelerate atherosclerosis. JACC
Here’s what I explained:
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Chronic inflammation injures the endothelium (the vessel lining), impairing nitric-oxide signaling and increasing permeability so lipoproteins can enter the arterial wall and form plaque — even when standard cholesterol looks “normal.” PMC+1
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Autoimmune activation keeps the immune system “on,” sustaining cytokine-driven vascular inflammation and accelerating atherosclerosis—a pattern well described across autoimmune diseases. PMC+1
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Some IBD (Inflammatory Bowel Disease) therapies can influence cardiovascular risk profiles. For example, systemic corticosteroids may worsen blood pressure, glucose, and lipids, whereas anti-TNF-α therapy has been associated with lower cardiovascular event rates, likely via inflammation control. (Clinical context matters; the primary goal is tight disease control.) MDPI+1
Bottom line: inflammation anywhere in the body can affect the heart and vessels. In IBD, addressing both gut disease activity and traditional risk factors is key to protecting long-term cardiovascular health. JACC
🩺 Ask Dr. Cruz
Question: Do I need a calcium score if my cholesterol is normal?
➡️ ANSWER: YES
Why?
Cholesterol is just one piece of the heart health puzzle.
Coronary artery disease can also be driven by high blood pressure, inflammation, family history, and genetics. Even with normal cholesterol, plaque can still build silently in the arteries.
That’s where a coronary calcium score comes in — a simple, noninvasive scan that shows whether calcium deposits (a sign of hard plaque) are already present. For many people, it helps refine risk beyond lab results and guides whether more aggressive prevention is needed.
In my practice, I often take this one step further with a CT angiogram, which can also detect soft plaque — the more unstable, high-risk type of plaque that calcium scoring alone can’t reveal. It’s a more thorough way of identifying plaque and evaluating heart attack risk.