Rethinking Carbs: A Cautious Look at Dr Mercola’s Argument

Bryan Mercadente might have been the better person to write this piece. His interest in nutrition and health is not so much abstract as lived and passionate. He thinks in recipes and routines, not just ratios and theories. I’m more cautious. Still, I’ll do my best to be fair to Dr Mercola’s argument, even if some of it strikes me as slightly overcooked.

Dr Mercola’s recent article, “The Hidden Health Benefit of Carbohydrates,” sets out to defend a food group many in alternative health circles have condemned. In particular, he claims that healthy carbohydrate consumption supports metabolic flexibility, enhances carbon dioxide (CO₂) production, and improves oxygen delivery at the cellular level. In his telling, carbohydrates are wrongly maligned by the keto-fasting crowd, and we risk undermining our health by treating them as the enemy.

It’s not an unreasonable starting point.

There is good evidence that metabolic flexibility—the ability to switch between burning fat and carbohydrates efficiently—is a marker of health.¹ People with metabolic syndrome often lose this ability. In that sense, promoting flexibility over rigid macronutrient allegiance is wise.

Mercola is also right to highlight the importance of whole-food carbohydrates. Fruits, tubers, properly prepared grains—these are not the same as ultra-processed sugar delivery systems, and it’s dishonest to lump them together. Many traditional diets with high carbohydrate intake are associated with long, healthy lives.²

Where things start to slide is in how confidently Mercola builds a theory around CO₂.

He argues that carbohydrate metabolism increases CO₂ output, which then promotes oxygen delivery via the Bohr effect. This is technically true, but the physiological significance is much harder to pin down. The body’s oxygen delivery system is regulated by many variables. CO₂ plays a role, but the leap to “carbohydrates improve oxygen delivery” is too large for the evidence he provides.³

The real issue with Mercola’s piece isn’t that it’s mad. It’s that it oversimplifies. He implies that avoiding carbohydrates reduces insulin sensitivity. That’s not consistently true. In insulin-resistant individuals, low-carbohydrate diets often improve glycaemic control and lipid markers.⁴

Then there’s his claim that chronic low-carb eating leads to systemic rigidity and decreased stress tolerance. That might be true in some cases—but it’s not a general law of biology. And he frames it as if it were.

There is also something almost spiritual in his appeal to nasal breathing and CO₂ retention techniques, which, while not without precedent in breathwork research, border on mystical when connected to carbohydrate metabolism.

In fairness, there is value in what Mercola is doing here. He’s pushing back against a simplistic macronutrient war that has lasted too long. For years, fat was the villain. Then it was carbs. Then it was seed oils.

He reminds us that the body is more adaptable than we think—and that balance, variety, and quality still matter more than obsession with macronutrient ratios.

But Mercola’s tone often works against his message. Instead of acknowledging complexity, he insists that he’s revealing a suppressed truth. Instead of noting that some low-carb diets are useful short-term tools but problematic long-term strategies, he suggests that most people are slowly suffocating at a cellular level from carbohydrate deficiency.

If he could let the science breathe a little more and the polemics a little less, he might persuade a wider audience.

Carbohydrates are not poison. Nor are they a panacea. They are a tool, and like any tool, they can be used well or badly. If Mercola wants to argue that health comes not from avoidance but from intelligent use, I’ll listen. But if he wants to convince us that CO₂ is the hidden hero of human physiology and that sweet potatoes are the key to metabolic salvation, I’ll have to ask for better evidence.

Still, this piece is more thoughtful than many of his others. There are insights buried beneath the exaggeration. Even Bryan, I suspect, would nod at some of it—though he might then return to his tofu, muttering about insulin and mitochondrial stress.

Footnotes

Kelley, D. E., et al. (2002). “Skeletal muscle fatty acid metabolism in association with insulin resistance, obesity, and weight loss.” American Journal of Physiology-Endocrinology and Metabolism, 283(4), E733–E743.
Buettner, D. (2012). The Blue Zones: Lessons for Living Longer From the People Who’ve Lived the Longest. National Geographic Books.
Roughton, F. J. W., & Root, R. K. (1945). “The Bohr Effect and the Oxygen Dissociation Curve of Human Blood.” Proceedings of the Royal Society of London. Series B, Biological Sciences, 132(868), 298–312.
Hallberg, S. J., et al. (2018). “Effectiveness and Safety of a Novel Care Model for the Management of Type 2 Diabetes at One Year: An Open-Label, Non-Randomized, Controlled Study.” Diabetes Therapy, 9(2), 583–612.