Walnuts may be good for the gut and help promote heart health

January 16, 2020

Science Daily/Penn State

Researchers found that eating walnuts daily as part of a healthy diet was associated with increases in certain bacteria that can help promote health. Additionally, those changes in gut bacteria were associated with improvements in some risk factors for heart disease.

Walnuts may not just be a tasty snack, they may also promote good-for-your-gut bacteria. New research suggests that these "good" bacteria could be contributing to the heart-health benefits of walnuts.

In a randomized, controlled trial, researchers found that eating walnuts daily as part of a healthy diet was associated with increases in certain bacteria that can help promote health. Additionally, those changes in gut bacteria were associated with improvements in some risk factors for heart disease.

Kristina Petersen, assistant research professor at Penn State, said the study -- recently published in the Journal of Nutrition -- suggests walnuts may be a heart- and gut-healthy snack.

"Replacing your usual snack -- especially if it's an unhealthy snack -- with walnuts is a small change you can make to improve your diet," Petersen said. "Substantial evidence shows that small improvements in diet greatly benefit health. Eating two to three ounces of walnuts a day as part of a healthy diet could be a good way to improve gut health and reduce the risk of heart disease."

Previous research has shown that walnuts, when combined with a diet low in saturated fats, may have heart-healthy benefits. For example, previous work demonstrated that eating whole walnuts daily lowers cholesterol levels and blood pressure.

According to the researchers, other research has found that changes to the bacteria in the gastrointestinal tract -- also known as the gut microbiome -- may help explain the cardiovascular benefits of walnuts.

"There's a lot of work being done on gut health and how it affects overall health," said Penny Kris-Etherton, distinguished professor of nutrition at Penn State. "So, in addition to looking at factors like lipids and lipoproteins, we wanted to look at gut health. We also wanted to see if changes in gut health with walnut consumption were related to improvements in risk factors for heart disease."

For the study, the researchers recruited 42 participants with overweight or obesity who were between the ages of 30 and 65. Before the study began, participants were placed on an average American diet for two weeks.

After this "run-in" diet, the participants were randomly assigned to one of three study diets, all of which included less saturated fat than the run-in diet. The diets included one that incorporated whole walnuts, one that included the same amount of alpha-linolenic acid (ALA) and polyunsaturated fatty acids without walnuts, and one that partially substituted oleic acid (another fatty acid) for the same amount of ALA found in walnuts, without any walnuts.

In all three diets, walnuts or vegetable oils replaced saturated fat, and all participants followed each diet for six weeks with a break between diet periods.

To analyze the bacteria in the gastrointestinal tract, the researchers collected fecal samples 72 hours before the participants finished the run-in diet and each of the three study diet periods.

"The walnut diet enriched a number of gut bacteria that have been associated with health benefits in the past," Petersen said. "One of those is Roseburia, which has been associated with protection of the gut lining. We also saw enrichment in Eubacteria eligens and Butyricicoccus."

The researchers also found that after the walnut diet, there were significant associations between changes in gut bacteria and risk factors for heart disease. Eubacterium eligens was inversely associated with changes in several different measures of blood pressure, suggesting that greater numbers of Eubacterium eligens was associated with greater reductions in those risk factors.

Additionally, greater numbers of Lachnospiraceae were associated with greater reductions in blood pressure, total cholesterol, and non-HDL cholesterol. There were no significant correlations between enriched bacteria and heart-disease risk factors after the other two diets.

Regina Lamendella, associate professor of biology at Juniata College, said the findings are an example of how people can feed the gut microbiome in a positive way.

"Foods like whole walnuts provide a diverse array of substrates -- like fatty acids, fiber and bioactive compounds -- for our gut microbiomes to feed on," Lamendella said. "In turn, this can help generate beneficial metabolites and other products for our bodies."

Kris-Etherton added that future research can continue to investigate how walnuts affect the microbiome and other elements of health.

"The findings add to what we know about the health benefits of walnuts, this time moving toward their effects on gut health," Kris-Etherton said. "The study gives us clues that nuts may change gut health, and now we're interested in expanding that and looking into how it may affect blood sugar levels."

https://www.sciencedaily.com/releases/2020/01/200116112542.htm

Abnormal gut bugs tied to worse cognitive performance in vets with PTSD and cirrhosis

Study involved more than 90 combat veterans

September 12, 2019

Science Daily/Veterans Affairs Research Communications

A study involving military veterans with PTSD and cirrhosis of the liver points to an abnormal mix of bacteria in the intestines as a possible driver of poor cognitive performance -- and as a potential target for therapy.

The study appeared Aug. 28, 2019, in the American Journal of Physiology.

Lead author Dr. Jasmohan Bajaj says the findings add to the substantial evidence linking gut health and brain function. He says they offer particular hope for people with PTSD and cirrhosis -- a common combination in the VA patient population.

"There is room for improvement in terms of the response to current therapies for PTSD," he says. "Targeting the gut microbiota might be an effective way to address the altered gut-brain axis in these patients and improve cognitive function, as well as other parameters of mental and physical health."

Bajaj is a physician-researcher with the McGuire Veterans Affairs Medical Center and Virginia Commonwealth University in Richmond.

Cirrhosis, or scarring of the liver, is prevalent in veterans with PTSD. Common causes include alcohol use disorder, obesity, and hepatitis C. Some patients with cirrhosis develop a complication called hepatic encephalopathy, which affects brain function. They become mentally sluggish and confused, and in severe cases can even lose consciousness.

PTSD, for its part, can also impair cognition. This can occur whether or not patients are taking drugs, such as antidepressants or sedatives, that act on the brain.

The researchers wanted to tease out the impact of abnormal gut microbiota in these conditions, and see whether those with cirrhosis and PTSD had different gut profiles than those with cirrhosis but no PTSD.

Bajaj's team took stool samples from 93 male veterans with cirrhosis, about a third of whom had combat-related PTSD. The other men had been exposed to combat during their military service but had not developed PTSD.

All the veterans completed a battery of cognitive exams. The tests covered areas such as reaction time, spatial ability, memory, and problem-solving.

Compared with the non-PTSD group, the men with PTSD had poorer cognitive performance.

Those with PTSD had microbiota that were less diverse, meaning they had fewer types of bacteria overall. This was true even after the researchers controlled for severity of cirrhosis, prior episodes of hepatic encephalopathy, alcohol use, and psychotropic medication use.

These veterans, along with the relative lack of diversity in their gut, tended to have more potentially harmful types of bacteria, such as Enterococcus and Escherichia/Shigella, and fewer beneficial ones, such as Lachnospiraceae and Ruminococcaceae.

In the study, higher levels of Enterococcus were associated with worse cognitive performance. The Ruminococcaceae family of bacteria, among others, was associated with better performance.

Ruminococcaceae bacteria are prevalent in healthy guts. These beneficial bugs help break down complex carbohydrates, such as those in unprocessed whole grains and legumes. People with healthier diets of this type tend to have higher counts of these organisms.

The same bacteria have been found to be scarcer in people with depression. There has been little study of their role in PTSD.

Could it be that the psychiatric drugs often used to treat PTSD affected these patients' microbiota? The study found that veterans with PTSD had similar gut profiles regardless of what medications they were on for the condition. This suggests the altered gut microbiome is a result of PTSD itself, and not any drug treatment.

One question the study couldn't answer was whether the combat trauma that triggered PTSD also triggered the bacterial changes, or whether those changes resulted over time from the chronic stress of PTSD.

Bajaj says it's hard to tease out that answer without prospectively following service members and veterans over many years, starting from before their deployments, and periodically sampling their gut bacteria. Such a study would be difficult to conduct.

In any case, he believes it's possible that restoring the gut microbiota to a healthy, normal balance could help ease PTSD symptoms -- especially when cirrhosis is also in play. But that idea has to be validated in studies.

"We need more research, including basic lab studies and clinical trials, to understand whether therapies that can change the gut microbiota can help these patients, and which particular types of bacteria are most beneficial," says Bajaj. He cited probiotic supplements or fecal transplants as two possible therapy approaches.

Recently, VA's Office of Research and Development launched an initiative to increase the number of such studies. Bajaj was among a group of more than 20 clinicians and biomedical scientists who helped develop a "roadmap" outlining VA's plans to fund work in this area over the next few years.

https://www.sciencedaily.com/releases/2019/09/190912165122.htm