A new study published in The Journal of Clinical Endocrinology & Metabolism found that a ketogenic diet significantly increased cerebral blood flow and the levels of a protein that supports brain health in cognitively healthy adults. The findings suggest that this dietary approach, often associated with weight loss and epilepsy treatment, may also enhance brain function in people without cognitive impairment.
Under normal dietary conditions, the brain relies heavily on glucose for fuel. However, when carbohydrate intake drops significantly, the body shifts into a metabolic state known as ketosis. In this state, the liver converts fat into ketone bodies—mainly β-hydroxybutyrate, acetoacetate, and acetone—which can cross the blood-brain barrier and serve as an alternative energy source for the brain.
A ketogenic diet is designed to mimic the effects of fasting by drastically reducing carbohydrate intake and increasing fat consumption. Typically, this type of diet provides around 70–75% of calories from fat, 20% from protein, and only 5–10% from carbohydrates. The goal is to shift the body’s metabolism toward fat oxidation and ketone production.
The rationale behind the study was based on emerging evidence that ketone bodies might not only serve as a backup fuel source for the brain but could also have direct benefits for brain health. Previous research has shown that individuals with mild cognitive impairment and Alzheimer’s disease often have difficulty using glucose effectively in the brain. Because ketones bypass some of the pathways affected in these conditions, they may help compensate for impaired glucose metabolism and restore energy balance.
In addition to acting as fuel, ketone bodies may also influence brain signaling pathways, inflammation, and the production of protective proteins such as brain-derived neurotrophic factor (BDNF), which supports neuron survival and synaptic function. The researchers wanted to find out if these benefits would also apply to cognitively healthy individuals.
To test their hypothesis, the scientists conducted a controlled trial involving 11 cognitively healthy adults who were between the ages of 50 and 70 and classified as overweight. Each participant completed two separate three-week dietary periods in a crossover design, meaning they tried both a ketogenic diet and a standard diet in different phases of the study. There was a one-week break between the two phases. The order of diets was randomized.
During the ketogenic diet phase, participants consumed a high-fat, low-carbohydrate diet designed to trigger the production of ketone bodies—molecules the body uses for energy when carbohydrate intake is limited. The diet was composed of approximately 75% fat, 20% protein, and only 5% carbohydrates. Participants were instructed on what to eat and monitored their blood ketone levels twice daily using a flash monitoring device. Those who did not achieve a certain level of ketones in the first week were excluded. During the standard diet phase, participants followed the Nordic Nutrition Recommendations, which emphasize a more conventional balance of carbohydrates, fats, and proteins.
To assess the impact of each diet, the researchers used a combination of advanced brain imaging techniques. At the end of each diet phase, participants underwent a brain scan using positron emission tomography (PET) to measure blood flow in different regions of the brain. Magnetic resonance imaging (MRI) scans were also performed to help align and interpret the PET data. On the same day as the PET scan, blood samples were collected to measure levels of the ketone molecule β-hydroxybutyrate and the neurotrophic protein BDNF.
The results showed that the ketogenic diet significantly elevated both ketone levels and brain-related outcomes. After three weeks on the ketogenic diet, participants’ blood levels of β-hydroxybutyrate increased more than twelvefold compared to the standard diet. This biochemical marker confirmed that participants had entered a state of nutritional ketosis. More importantly, cerebral blood flow was 22% higher on average during the ketogenic phase compared to the standard diet. This increase was observed across multiple regions of the brain and was measured with a high level of precision using PET imaging.
In addition to improved blood flow, the researchers found that levels of BDNF were 47% higher during the ketogenic diet phase. BDNF is a protein that plays a key role in the growth, maintenance, and survival of neurons. It is often described as “fertilizer” for the brain and is believed to support learning and memory. Reduced BDNF levels have been linked to neurodegenerative diseases such as Alzheimer’s. While previous research had shown that ketone supplements could increase BDNF in the short term, this study demonstrated that sustained nutritional ketosis can also elevate BDNF levels over time.
The study also found a strong correlation between blood ketone levels and cerebral blood flow across the two diet phases. In other words, higher ketone concentrations in the blood were associated with greater brain perfusion. This relationship adds further weight to the idea that ketone metabolism plays a direct role in improving brain function, even in the absence of cognitive deficits.
Although the sample size was small—only 11 participants completed the full protocol—the findings were consistent across individuals and backed by rigorous imaging and biochemical assessments. The authors noted that nine participants completed both PET scans, and BDNF data were available for ten participants. Importantly, no serious side effects were reported, and all participants successfully reached and maintained a ketotic state during the ketogenic phase.
The research builds on earlier findings from studies involving people with mild cognitive impairment or Alzheimer’s disease, who often experience decreased cerebral blood flow. In those populations, ketogenic diets or ketone supplements have been associated with improvements in brain energy metabolism and function. However, it was previously unclear whether the same benefits would extend to healthy individuals without signs of cognitive decline. This new study fills that gap by showing that a ketogenic diet can enhance both blood flow and neurotrophic support in people without existing brain disorders.
Low cerebral blood flow has been linked to future cognitive decline in both patients and healthy individuals. Several studies have shown that people with lower blood flow in certain brain areas are more likely to experience memory problems and reduced executive functioning over time. By increasing cerebral perfusion, a ketogenic diet might help protect against such decline, although more research is needed to confirm that possibility.
The researchers also highlighted the potential importance of BDNF in brain aging. BDNF helps regulate synaptic plasticity, the ability of the brain to adapt and reorganize itself, which is vital for learning and memory. Lower BDNF levels are commonly observed in people with moderate to severe Alzheimer’s disease. Raising BDNF through diet or other interventions might improve neural resilience and delay the onset of cognitive symptoms.
One of the study’s limitations is the small number of participants. While the crossover design helps control for individual variability, a larger sample size would be needed to confirm the generalizability of the results. Another limitation is that the study only included individuals who were overweight, which means the findings might not apply to people of normal weight or those with different metabolic profiles. Additionally, the intervention lasted just three weeks per diet phase. It is not yet known whether these effects would persist or grow stronger with longer-term adherence to a ketogenic diet.
Future research could explore whether similar improvements in cerebral blood flow and BDNF occur in other populations, such as people at risk of dementia, individuals with metabolic syndrome, or even younger adults. Studies could also examine whether these physiological changes translate into measurable improvements in cognitive performance. Finally, it would be useful to compare different types of ketogenic diets, such as those based on plant-based fats versus animal fats, to assess how various nutritional sources influence brain health.
The study, “A 3-Week Ketogenic Diet Increases Global Cerebral Blood Flow and Brain-Derived Neurotrophic Factor,” was authored by Thien Vinh Luong, Kim Vang Hansen, Allan Kjeldsen Hansen, Stephen C. Cunnane, Niels Møller, Esben Søndergaard, Lars Christian Gormsen, and Mads Svart.
