Lactate: The Ultimate Health Biomarker?

Summary

• Lactate is a vital fuel, not just a waste product, serving as an energy source for the heart, brain, and oxidative muscle fibers through the lactate shuttle.
• Metabolic health and mitochondrial "flexibility" dictate lactate metabolism
• Efficient mitochondria allow the body to transition between fat, glucose, and lactate as energy sources; dysfunction leads to excessive glucose dependence and metabolic issues.
• Acute lactate surges are beneficial: High-intensity exercise-induced lactate spikes enhance mitochondrial biogenesis, muscle recovery, and cognitive function.
• Chronic lactate elevation signals metabolic dysfunction: Persistently high levels are linked to insulin resistance, inflammation, and inefficient energy production.
• Lactate has systemic effects beyond muscles: It influences brain function, immune responses, cardiovascular health, and even cancer metabolism
• Optimizing metabolism enhances lactate utilization: Strategies like Zone 2 training, high-intensity exercise, strength training, and metabolic health-focused nutrition improve lactate clearance and efficiency.
• Lactate monitoring could provide deep insights into our metabolic stress and health long before typical measures like Hemoglobin A1c start to rise.

Let's start here... with the following elegant graph. It showslactate levels if we are sedentary (MtS), moderately active (MA), or elite level (PA) activity. The more activity we can sustain (X-axis) before an elevation in lactate (Y-axis) says a lot about our overall health, absent any other biomarkers. We can also predict many other medical problems by seeing where someone is on these curves. Lactate is that important.

Reminder

Lactate: More Than Just a Fatigue Byproduct

Lactate has long been misunderstood, often labeled as the culprit behind muscle fatigue and soreness. However, modern research has reshaped our understanding: lactate is a crucial fuel source, not just a waste product.

It is a key player in energy metabolism, athletic performance, and overall health. But when metabolic flexibility declines, lactate’s role shifts—as the body favors excessive glucose utilization which contributes to systemic dysfunction. Understanding how lactate functions and how to optimize its role is essential for long-term metabolic health and performance.

What is Lactate?

Lactate is a byproduct of anaerobic metabolism, produced when the body breaks down glucose for energy in low-oxygen conditions. This process can occur during intense exercise in healthy, active people, where oxygen demand exceeds supply. In people with poor metabolic health, lactate can rise with slow walking. Refer back to the graph above. Look at the baseline lactate levels on the far left of the X-axis. People who are unhealthy or sedentary have higher resting lactate levels. Furthermore, sedentary people experience a rapid increase in lactate with walking, whereas trained athletes can remain at their baseline level until they are doing hard efforts for a while.

Lactate is not a metabolic dead end. Instead, it is an essential intermediary that can be shuttled to the liver and slow-twitch muscle fibers. Lactate from fast-twitch muscle fibers returns to type 1 oxidative fibers and enters the cell via the MCT-1 receptor. Once in the cell, it can be converted to pyruvate, which can be turned into energy via the TCA cycle.

Furthermore, when the lactate produced in the muscle goes to the liver it can be converted to glucose and then returned to the muscle as fuel, which is known as the Cori cycle.

These pathways ensure lactate is efficiently reused rather than accumulating in the bloodstream. Both of these mechanisms to utilize lactate are trainable. This means that exercise or activity improves our ability to shuttle lactate around, allow it to enter the cells, and efficiently utilize it as a fuel substrate.

The ability to produce and clear lactate efficiently is a hallmark of metabolic health and proper metabolic flexibility, which occurs when the body easily transitions between different fuel sources—fatty acids, glucose, and lactate—depending on energy demands. A loss of this flexibility can lead to metabolic dysfunction and impaired endurance.

Lactate as a Fuel

Far from being a metabolic dead end, lactate is a preferred fuel source for the heart, brain, and mitochondria-rich tissues. The ability to produce and utilize lactate as a fuel implies good metabolic health.

During exercise, lactate is shuttled to oxidative muscle fibers (Type I fibers) and converted into pyruvate, which feeds into the Krebs cycle for efficient energy production. This process, known as the lactate shuttle, highlights its critical function in sustaining prolonged effort and supporting recovery. Type II or fast twitch fibers, active at higher intensities, push out vast amounts of lactate. When the lactate shuttle is robust and functioning well, you can sustain high-intensity exercise for longer because the lactate is not building up rapidly. Instead, it is being shuttled back to the Type I fibers for fuel.

Our ability to efficiently utilize lactate also depends on mitochondrial flexibility—the ability of our cells to switch between different fuel sources (fatty acids, glucose, and lactate). Our metabolism becomes skewed when this flexibility is lost, leading to excessive glucose dependence and chronic metabolic dysfunction.

There are many reasons why we see a rise in lactate occurring in sedentary people at rest and with low-intensity efforts, such as walking. They have fewer mitochondria. Those mitochondria aren't working as well, nor are they as efficient. The capillaries are less abundant–thus, there is less blood flow to bring oxygen or dispose of end-products. Along with the loss of mitochondrial flexibility and instability to shuttle lactate back to type I fibers, explain why sedentary people have trouble processing lactate— a key sign of poor metabolic health.

Insulin resistance (some estimate a prevalence of nearly 90%) and other metabolic disorders, which are extremely common in our population, dramatically impede our metabolic flexibility, leading to excessive glucose dependence and chronic metabolic disease.

Loss of Mitochondrial Flexibility and Its Consequences

Mitochondrial dysfunction (oxidative stress) is a hallmark of aging and metabolic disease. In a metabolically flexible state, the body efficiently transitions between fat oxidation at rest and glucose utilization during exertion. But when mitochondria lose this adaptability, lactate processing becomes impaired, leading to:

• Increased reliance on glucose metabolism, which promotes insulin resistance and systemic inflammation.
• Poor lactate clearance results in persistently elevated lactate levels and a greater risk of metabolic inflexibility.
• Reduced oxidative efficiency, leading to early fatigue and impaired recovery.

This shift contributes to the onset of type 2 diabetes, cardiovascular disease, and even neurodegenerative disorders, where energy supply-demand mismatches create cellular stress.

Preview of What's Ahead

• Audio Version (for subscribers only)
• Lactate’s Dual Role: Acute vs. Chronic Elevation
• Distant Effects of Lactate Beyond the Muscle Cell
• Optimizing Metabolism: Harnessing Lactate for Better Health
• Continuous Lactate Monitoring: The Future... which is not so far away
• Conclusion

Audio Version (for subscribers only)