The Fuel Your Brain Is Begging For

We have been told a story about the aging brain: your genes were dealt a certain hand, the clock runs down, and one day the lights start to dim. In that story, dementia is something that happens to you. This article — Part 1 of the Starved Brain series from Dr. Gurpreet Padda at Regen.MD — makes the case that, for most people, this story is wrong at the root. It starts with the most basic question almost everyone gets wrong: what does your brain actually run on?

Your brain’s preferred fuel is not sugar

Ask a hundred people what powers the brain and ninety-nine will say glucose — sugar. It is in every textbook diagram. It is also not the brain’s first choice.

When ketones — the clean-burning fuel your body makes from fat — are available in the bloodstream, the brain preferentially burns them. Not as a backup, as a preference. Large portions of the brain will run on ketones and fat as long as they are supplied, and fall back on glucose only when ketones run out.

This is not a fringe claim; it can be watched directly. Using PET imaging — the same scans used to hunt for cancer by tracking glucose uptake — researchers have put people into deeper ketosis and measured ketones rising to supply roughly sixty to seventy percent of the brain’s energy, even while glucose sat at normal levels, available and ignored. The brain had a choice, and it chose fat.

Why would evolution wire the most important organ in your body to prefer a fuel most modern people almost never produce? Because for almost all of human history we did produce it. Fat-adapted, meat-eating, periodically fasting humans lived in gentle, on-and-off ketosis as a baseline. The brain did not evolve on a river of sugar.

The starving brain, on a scan

Here is where it turns urgent. In Alzheimer’s disease, one of the earliest and most consistent findings — appearing years, sometimes decades, before memory symptoms — is that the brain’s ability to take up and use glucose falls. Regions of the brain quite literally lose the ability to burn their sugar, and the dimming is visible on a PET scan before a patient has forgotten a single name.

For a long time we assumed that dimming was the disease — dying cells using less fuel. But a second finding reframes everything: when you measure ketone uptake in those same Alzheimer’s brains, it is largely preserved. The cells that can no longer burn sugar can still burn ketones. The engine is not dead. It has been handed a fuel it can no longer process — while the fuel it can process is nowhere in the modern diet.

This is why a growing number of researchers describe Alzheimer’s disease as “type 3 diabetes”: a state of insulin resistance and energy failure localized to the brain. The landmark review that named it laid out the case in 2008, and the evidence has accumulated since.

The fuel was always the point — from birth

The wiring runs deep, and it starts before birth. Pregnancy has been described by metabolic researchers as “accelerated starvation”: as pregnancy advances, mothers slip into ketosis faster and more easily than anyone else. Those ketones cross the placenta freely, and the rapidly growing fetal brain of the third trimester requires them — both as fuel and as raw material for the fats that physically build the brain.

It does not stop at birth. Breast milk is deliberately ketogenic — even with the milk sugar lactose present, breastfed infants run on ketones, and studies comparing breastfed to formula-fed infants find the formula-fed babies produce measurably fewer ketones. The default state of the human brain, from its first days, is to be fueled by fat and ketones and built from fat.

And here is the tell that this is a diet story and not simply an aging story: we do not have a single documented example of a wild animal, on its natural diet, whose brain shrinks as it ages. Our closest relatives, chimpanzees, were studied across the full adult lifespan — and while human brains predictably shrank, the chimpanzee brains did not.

The honest read on the evidence

Precision is how you know you can trust the rest of this series, so here are the limits of these findings stated plainly. The authors of that chimpanzee study attributed the human-specific shrinkage mainly to our unusually long lifespan, not directly to diet — that is their honest read, and it is worth honoring. Separately, a 2024 study of domestic pigs versus wild boar found smaller brains in the grain-fed domestic animals, but the reduction was not statistically airtight, and the pigs bred hardest for muscle actually had larger brains. What that study cleanly proves is not “grain shrinks brains.” It is the deeper point this series rests on: brain size is not fixed — it responds to environment and nutrition. The brain is plastic, and diet is one of the hands that shapes it.

What this means for your evaluation

Step back and reframe. We look at brain scans of older adults, see shrinkage, and call it “normal age-related atrophy.” But we have a brain that prefers a fuel most modern people never make, a disease process defined by that brain starving of the sugar it can no longer burn, and every other animal in nature aging without this shrinkage. What if what we call normal aging of the brain is, for many people, what decades of quiet metabolic starvation look like, etched into an organ?

That is a testable question, not a verdict. At Regen.MD we do not guess about it — we measure your metabolic and fuel status to see whether your brain is living in the energy crisis described here, and whether it can be moved toward ketone-based fuel safely, accounting for every medication you take. A starving brain is potentially a fixable brain, and the first step is knowing whether yours is starving at all.

Frequently asked questions

Key takeaways

• The brain runs efficiently on ketones and appears to prefer them; in Alzheimer’s, glucose uptake fails years before symptoms while ketone uptake is largely preserved.
• This pattern is why some researchers call Alzheimer’s “type 3 diabetes” — an energy crisis localized to the brain.
• The evidence that diet shapes brain size is real but honestly limited; what is well supported is that brain size is plastic and responds to nutrition.
• The actionable step is measuring your own metabolic and fuel status — not self-starting a diet — because a starving brain may be a fixable one.

Medically reviewed by Gurpreet Singh Padda, MD — Board Certified in Anesthesiology, Pain Medicine, Interventional Pain Management, Addiction Medicine, and Obesity Medicine. Last reviewed July 2026.

This article is educational and is not a substitute for evaluation, diagnosis, or treatment by a physician. Individual results vary. Do not start, stop, or change any medication or diet without consulting your physician — this is especially important if you take medication for diabetes or blood pressure. To have your metabolic and cognitive terrain evaluated, apply for a Clinical Evaluation at Regen.MD or call (314) 295-3000 / text (314) 886-5902.

References

1. de la Monte SM, Wands JR. Alzheimer’s disease is type 3 diabetes — evidence reviewed. J Diabetes Sci Technol. 2008;2(6):1101-1113.
2. Sherwood CC, Gordon AD, Allen JS, et al. Aging of the cerebral cortex differs between humans and chimpanzees. Proc Natl Acad Sci USA. 2011;108(32):13029-13034.
3. Cucchi T, Neaux D, Féral L, et al. How domestication, feralization and experience-dependent plasticity affect brain size variation in Sus scrofa. R Soc Open Sci. 2024;11(9):240951.