People with early-stage Alzheimer's disease may be able to slow their cognitive decline through diet and exercise, according to a new study.

Participants who adhered to a daily mix of aerobic exercise and a mostly plant-based diet slowed cognitive decline, however, memory and thinking worsened for members of a control group who didn't change their habits, according to the study published Friday in Alzheimer's Research and Therapy. The study was conceptualized by Dean Ornish, a physician and researcher whose rigorous diet and lifestyle recommendations to combat chronic disease have generated debate over the years among medical researchers.

Researchers cautioned that the results must be replicated before broader conclusions can be drawn. The study enrolled just 51 people, in part, due to difficulties posed by the COVID-19 pandemic.

But the small-scale multi-state study suggests lifestyle changes might be another way to combat Alzheimer's, a mind-robbing disease that afflicts 6.9 million Americans, they say. The disease has stymied researchers and drug companies that have poured billions into developing drugs targeting beta-amyloid protein that accumulates in the brains of Alzheimer's patients.

After all that investment, only two drugs, Leqembi and Aduhelm, have won Food and Drug Administration approval, and the maker of Aduhelm halted sales and relinquished ownership of the drug. An FDA advisory committee next week will evaluate donanemab, an anti-amyloid drug made by Eli Lilly.

Dr. Rudy Tanzi, director of the McCance Center for Brain Health at Massachusetts General Hospital and co-author of the diet and exercise study, said the new research suggests a vegetarian diet and regular exercise reduced amyloid in patients.

"It's almost like a mini-Leqembi result," said Tanzi, referring to the amyloid-clearing drug that won FDA approval last year. "So it's pretty astonishing."

Researchers not involved in the study say while the results are promising, they'd like to see larger studies into the effects of diet and exercise on people with Alzheimer's.

"It was a very small sample," said Laura Baker, a Wake Forest University School of Medicine professor of gerontology and geriatric medicine. "This does not provide definitive answers yet."

Vegetarian diet, aerobics and supplements

The study included 51 people in the early stages of Alzheimer's disease who were randomly assigned to a group that adopted regular exercise and dietary changes or a control group whose members did not take such actions. The researchers measured the cognition and function of the two groups using several commonly used tests in Alzheimer's research. The study found that lifestyle changes "may improve cognition and function" after 20 weeks. The control group had worsening signs of disease, the study reported.

The participants were shipped 21 plant-based meals and snacks each week consisting of fruits, vegetables, whole grains, legumes, soy products, seeds and nuts. They were asked to follow the diet strictly and take eight supplements and vitamins. Participants also took daily 30-minute walks, did strength-training movements three days per week and sought to manage stress through meditation, yoga or stretching for one hour each day.

To reinforce those actions, participants and their spouses or caregivers joined four-hour Zoom sessions three times each week to complete one hour of supervised exercise, one hour of stretching, one hour of a support group and a one-hour lecture on lifestyle changes.

Those who participated in the diet and exercise regimen all reported better scores on four common Alzheimer's tests when compared to individuals in the control group. Three of the tests yielded scores suggesting participants showed "improvement in cognition and function" and a fourth test revealed the participants in the regime showed less cognitive decline than the control group.

The study also said a measure of beta-amyloid in the blood favored those who dieted and exercised compared to the control group.

The lifestyle proponent behind the study

Ornish, a physician who has long supported lifestyle medicine as a means of combating chronic disease, secured research funding and was the study's principal investigator. He describes lifestyle medicine as including a plant-based diet, moderate exercise, meditation and support groups to prevent, slow or reverse the effects of heart disease and other chronic conditions. Using those same principles on Alzheimer's patients, he said, has the potential to combat the effects of the disease.

Ornish said decades ago, mainstream medicine thought that heart disease was irreversible. But lifestyle changes and medications have shown that heart disease often can be slowed or reversed, he said.

He believes this study shows Alzheimer's disease can be slowed similarly.

Despite the small number of participants, Ornish said the study was rigorous and backed by data.

"There's a common misconception that if it's not 1,000 people, then it's not a valid study," Ornish said. "But you can actually argue the other way around, that if it takes 1,000 people to show statistical significance, then it's not really a very powerful intervention."

He said the beta-amyloid levels, cognitive scores and other biomarker measures led researchers to conclude that lifestyle interventions worked.

The study reported two-thirds of patients in the control group worsened and none improved over 20 weeks. But 17 of 24 patients completing the diet and lifestyle changes either stabilized or improved their cognition and function scores.

"Looking through the lens of all these different measures, overall, these patients are, on average, clearly getting better in one group and worse in the other," Ornish said.

Study lacked racial, ethnic diversity

The study noted it had limitations, including a lack of racial and ethnic diversity among study participants. Participants also knew they were undergoing the diet and lifestyle regimen, and therefore, they might have anticipated positive results. To guard against a placebo effect, researchers told participants they did not know whether the lifestyle changes would work.

Baker, at Wake Forest, has also researched whether regular exercise from light stretching to rigorous aerobics, can help slow memory and thinking decline. Her research team expects to report results from a large study of more than 2,000 participants next year.

Baker said her research and Ornish's studies underscore the importance of heart health and potential benefits to long-term brain health.

However, she does not believe there is enough evidence to suggest Alzheimer's disease or other dementias can be reversed through diet and exercise. Such a claim would need to be bolstered by several large-scale studies, evidence that does not yet exist, she said.

"The idea that lifestyle intervention can reverse dementia or cognitive impairment – I just don't think there's enough evidence for that," Baker said. "And I think that's creating false hope right now."