Brain fog and stubborn weight gain often get treated as two separate complaints — one for a neurologist, one for a diet plan. Dr. Rob McCarthy, a chiropractor and functional medicine practitioner based in Greenville, North Carolina, spent this conversation with Mark Anthony making the case that they're frequently the same problem wearing two different masks: chronic inflammation, an overworked gut lining, and a blood sugar system stuck on a roller coaster.
McCarthy has practiced chiropractic in North Carolina for about 30 years. He spent his first five years doing, in his words, "exactly what every other chiropractor did" — adjusting patients for back and neck pain — until a patient diagnosed with fibromyalgia sent him looking for answers standard chiropractic couldn't give him. That search led him into functional medicine and, later, functional neurology, disciplines he now layers on top of his chiropractic training. His practice is in Greenville, home to East Carolina University's medical school, and draws patients from across Eastern North Carolina; he can be found at greenvillehealth.com.
Key Takeaways
- Brain fog and weight-loss struggles are often connected — in Dr. McCarthy's experience, if a patient deals with one for long enough, the other tends to follow.
- Chronic gut inflammation ("leaky gut") can lead to a leaky blood-brain barrier within hours, letting inflammatory compounds reach the brain — and an estimated 60 to 70% of leaky gut's symptoms show up outside the digestive tract entirely.
- Cortisol released from repeated blood-sugar swings specifically drives abdominal weight gain, which is why "eat less, move more" often isn't enough on its own.
- His intake process includes a 20-to-30-minute history, a functional neurological exam, three in-depth questionnaires, and a broader blood panel than a typical primary care visit — before any treatment plan is built.
- Vagus nerve stimulation, started in-office and continued at home for 30 minutes a day, is one tool he uses to support both brain function and gut function.
How Brain Fog and Weight Loss Are Connected
Asked whether brain fog and weight-loss struggles are related or separate issues, McCarthy said they're usually tied together — a patient can have one without the other, but rarely for long. He traces both back to inflammation. Chronic, low-grade gut inflammation can develop into what he calls leaky gut, where the intestinal lining becomes overly permeable. Within hours, he said, that permeability can extend to the blood-brain barrier as well, letting the same inflammatory compounds circulating in the blood reach the brain — which is the mechanism he points to behind brain fog itself.
He also pushed back on the assumption that leaky gut has to come with digestive symptoms. By his estimate, 60 to 70% of leaky gut's symptoms show up outside the digestive tract — in the joints, the nervous system, and the brain — which is why patients with no stomach complaints at all can still be dealing with it. McCarthy also pointed to a more recent driver of the same pattern: his practice currently has about a dozen active patients who were diagnosed with long COVID and sought him out after conventional providers told them there was nothing more to be done.
Inside a Visit: Finding the Root Cause Instead of Managing Symptoms
McCarthy contrasted his intake process with a typical five-minute primary care visit. He starts with a 20-to-30-minute comprehensive history, followed by a functional neurological exam to identify which areas of the nervous system aren't functioning well. Patients then take home three questionnaires — one covering the brain and neurotransmitters, a metabolic assessment form covering the stomach and intestines, and a brain-region localization form asking about symptoms tied to the frontal lobe, parietal lobe, cerebellum, and other specific areas. Those results, combined with a blood panel he described as more comprehensive than a standard CBC, chem panel, and TSH check, become the basis for an individualized plan — mapped out for the patient on a whiteboard.
One tool in that plan is vagus nerve stimulation, done in-office for the first couple of weeks and then continued at home with a take-home unit for 30 minutes a day. McCarthy said it supports both brain function and gut function, and specifically helps patients dealing with chronic constipation, which he described as one of the most common complaints he sees. He also discussed neuroplasticity — the brain's ability to build new, stronger neural pathways through repetition — as central to his approach with the frontal lobe specifically. He noted that roughly 80% of patients coming into his office are already taking some form of SSRI antidepressant, medications he said were originally approved by the FDA only for short-term use. Rather than staying on them indefinitely, he said some patients who improve frontal lobe function through his care are able to work with their own physician to taper off and feel better than they did on the medication.
"There's a big difference between normal and common. Here, especially in Eastern North Carolina, these things are very common. It doesn't make it normal."
— Dr. Rob McCarthyBlood Sugar, Cortisol, and Food Sensitivities: Why "Eat Less" Doesn't Work
McCarthy rejected the simple calories-in-calories-out model of weight loss. He described a cycle where blood sugar swings between hypoglycemia and insulin resistance — dropping low enough to trigger a cortisol release from the adrenal glands, which pushes blood sugar back up but also drives the body to store fat specifically around the abdomen. "You cannot lose weight with cortisol," he said — no amount of walking or dieting overrides it until blood sugar is stabilized first.
Food sensitivity testing is one way he works to break that cycle. Gluten and casein (the protein in milk) are the most common sensitivities he sees, but he said the more telling cases are patients reacting to foods like chicken, spinach, carrots, or onions — a sign of leaky gut rather than a typical allergy. Those foods get removed for a short period alongside a compound intended to help heal both the gut lining and the blood-brain barrier. Patients are also moved toward eating five to six times a day — three meals plus three snacks — to keep blood sugar stable and low-glycemic throughout the day rather than spiking and crashing. McCarthy described one recent patient, eight visits and about a month into that approach, who was down 10 pounds while eating six times a day on a real-food, anti-inflammatory diet — and reported clearer thinking as her brain fog lifted.
Who This Conversation Is For
If you've been told brain fog or a stalled metabolism is "just age," or you've tried diet after diet without lasting results, this episode is a plain-language look at how a functional medicine and functional neurology approach investigates the underlying inflammation, blood sugar, and gut issues that conventional visits often don't have time to address.
