What Two New Peanut Butter Studies Found About Muscle and Brain Health

Peanut butter has a reputation problem. It’s calorie-dense, often dismissed as a childhood food, and rarely shows up on lists of foods nutritionists actually recommend for adult health.

That may be about to change.

Two separate six-month randomized controlled trials, both published in peer-reviewed journals, found that daily peanut butter consumption produced measurable improvements in physical and cognitive health, with no weight gain observed in either group.

One was led by researchers at Deakin University in Australia, focused on older adults at risk of falls. The other, the ARISTOTLE study, was run at the University of Barcelona with healthy adults aged 18 to 33.

Same food. Two completely different populations. Both returned results that surprised the researchers running them.

What made the findings stand out isn’t just what peanut butter did. It’s what it didn’t do: nobody gained weight, and in both cases participants didn’t change their exercise habits.

The muscle study: 120 older adults, six months, three tablespoons a day

The first trial, published in the Journal of Cachexia, Sarcopenia and Muscle in February 2026, enrolled 120 adults aged 66 to 89. All were living independently but had been assessed as being at higher risk of falls.

Half were assigned to eat 43 grams of natural peanut butter daily (roughly three tablespoons). The other half maintained their usual diet and avoided nuts entirely.

Neither group changed their exercise routine. The trial ran from May 2023 to July 2024 at Deakin University’s Burwood Campus.

At the six-month mark, most measures of physical function showed no significant difference between the groups. Gait speed, balance, and upper-body strength were similar.

But two things stood out clearly. The peanut butter group completed the five-times sit-to-stand (5STS) test 1.23 seconds faster on average (95% CI: 2.09 to 0.37, p = 0.006).

They also generated significantly more muscle power in absolute terms (22.0 W more, p = 0.004) and relative to body weight (0.27 W/kg more, p = 0.002). The 5STS test is a standard clinical measure of fall risk and daily independence.

Dr. Sze-Yen Tan, associate professor at Deakin’s Institute for Physical Activity and Nutrition, summarised it directly: “Being able to complete the test faster means greater muscle power. Muscle power enables older people to perform activities of daily living.”

Why no weight gain? The calorie paradox worth understanding

Participants were adding roughly 250 extra calories to their diet every single day for six months. And yet body weight, BMI, and body composition showed no significant change in the peanut butter group compared to the control.

One explanation is displacement.

When people add a filling food high in protein, fat, and fibre, they often eat slightly less of something else without realising.

Researchers also suggest that the high protein and unsaturated fat content may improve metabolic efficiency.

They’re careful to note this remains a hypothesis, not a confirmed finding.

A second hypothesis involves arginine, an amino acid present in peanuts at around 1.2g per 43g serving. Arginine is a precursor to nitric oxide, which dilates blood vessels and improves blood flow to muscles.

Better muscle perfusion could help explain the power improvements seen in the trial.

This is especially plausible in older adults, whose vascular function naturally declines with age.

What’s actually in 43g of natural peanut butter

Nutrient (per 43g serving)AmountRole in bodyStudy linkVegan?Protein~10gMuscle repair, satietyMuscle power

Yes

Unsaturated fat

~13gHeart, inflammationBlood flow

Yes

Polyphenols

VariesGut-brain axisMemory, mood

Yes

Arginine (amino acid)

~1.2gVasodilationMuscle perfusion

Yes

Fibre

~1.5gMicrobiome supportCognitive health

Yes

Sources: USDA FoodData Central; Feyesa et al., J Cachexia Sarcopenia Muscle, 2026

The brain study: 63 young adults, the gut-brain axis, and what memory tests showed

The ARISTOTLE study, published in Clinical Nutrition and run at the University of Barcelona, tracked cognition and stress response in 63 healthy adults aged 18 to 33 over six months.

Participants were split into three groups. One ate 25g of skin-roasted peanuts daily, one ate 32g of peanut butter daily, and one ate 32g of a control butter made from peanut oil but stripped of fibre and phenolic compounds.

The control product matched the macronutrient profile of peanut butter exactly. That made it a genuinely rigorous comparison, because any difference in outcomes couldn’t be explained by calories or fat content alone.

Both the peanut and peanut butter groups improved on immediate memory scores compared to the control. Anxiety scores also dropped significantly in both groups.

The peanut butter group showed lower depression scores (p = 0.003). Urinary cortisol levels, a direct biochemical marker of stress, were also reduced.

What the gut-brain axis has to do with peanut butter

The researchers were explicit about the mechanism they believe is driving these results.

It’s the gut-brain axis, specifically the way dietary polyphenols interact with gut bacteria to produce compounds that influence brain chemistry.

Dr. Sara Hurtado-Barroso, co-author of the ARISTOTLE study, explained: “Prebiotic substances present in peanuts and peanut butter, such as polyphenols, may positively affect cognition and mood by promoting production of microbial phenolic metabolites.”

Peanut polyphenols aren’t fully absorbed in the small intestine.

They pass into the colon, where gut bacteria convert them into short-chain fatty acids (SCFAs) and other compounds that can reach the brain via the vagus nerve and hormonal pathways.

This is why the control butter showed no cognitive benefit despite having the same fat and calorie content. Without fibre and polyphenols, the gut-brain pathway had nothing to work with.

A 2025 review in Nutrition Reviews confirmed more broadly that gut microbiota-derived phenolic metabolites can cross the blood-brain barrier and exert measurable neurocognitive effects.

The link between plant-based diets and brain health is growing stronger with each study.​

What kind of peanut butter actually delivers these benefits

Both studies used natural, minimally processed peanut butter, the kind made from just peanuts with maybe a small amount of salt.

Neither used the heavily processed varieties that contain added palm oil, sugar, or emulsifiers.

The benefits appear to come from polyphenols and fibre concentrated in and near the peanut skin.

Participants eating skin-roasted whole peanuts saw slightly stronger anxiety reductions than those eating peanut butter, which suggests processing does reduce some bioactive content.

Practically speaking: look for peanut butter with one or two ingredients. If palm oil or glucose syrup appear on the label, it’s a different product from what either trial tested.

If you’re building a vegan protein base, natural peanut butter is one of the simplest options available. Two tablespoons delivers 7 to 8g of protein, meaningful fibre, and those polyphenols, typically for under $1.

What the studies don’t tell us yet

Neither trial is without limitations. The COINS muscle study enrolled a relatively small group, and the primary outcome (gait speed) didn’t reach statistical significance.

The muscle power improvements came from secondary outcomes. That’s still meaningful, but it’s worth being clear about what the study was actually powered to show.

The ARISTOTLE brain study had an even smaller sample of 63 participants. The authors noted that dropout during the COVID-19 lockdown reduced statistical power from the planned 80% to around 60%.

The study also wasn’t blinded, meaning participants knew which group they were in. That can influence self-reported mood scores, which is a real limitation.

Both studies were rigorous enough to be published in respected journals, and the mechanisms they propose are scientifically plausible. But this isn’t the moment to call peanut butter a cure for anything.

It’s the moment to notice that a whole-food plant ingredient most people already keep in their kitchen may be doing more than anyone expected.

Frequently asked questions

How much peanut butter did people eat in the studies?

The older adult trial used 43 grams per day, roughly three tablespoons. The brain study used either 25g of whole peanuts or 32g of peanut butter daily.

Did participants gain weight from eating peanut butter every day?

No. In both studies, no significant changes in body weight or composition were observed in the peanut butter groups compared to controls, despite the extra calories involved.

Does peanut butter have to be natural for these benefits?

The studies used minimally processed peanut butter and skin-roasted peanuts. The cognitive benefits were linked to polyphenols and fibre, which are reduced or absent in heavily processed products.

Is peanut butter good for older adults specifically?

The Deakin University COINS trial found significant improvements in sit-to-stand speed and muscle power in adults aged 66 to 89. Given that muscle power is closely tied to fall risk and independence, these findings are particularly relevant for that age group.

What is the gut-brain axis and how does peanut butter affect it?

The gut-brain axis is the communication network between the gastrointestinal system and the brain. Peanut polyphenols are converted by gut bacteria into metabolites that influence cognitive function and mood.

The ARISTOTLE study found that peanuts and peanut butter, but not a control butter without fibre or polyphenols, improved memory and reduced anxiety over six months.

Is peanut butter vegan?

Yes. Natural peanut butter is made from peanuts and nothing else, making it one of the most reliably plant-based foods available. You can explore more naturally vegan foods here.

The jar that was already in my kitchen

There’s something quietly satisfying about this kind of research. Not because it tells us peanut butter is magic, but because it confirms that a food most of us grew up with may have been doing more than we realised.

Both studies were conducted on people eating real food, not taking supplements. No capsules. No lab-engineered extracts. Just peanuts, in a jar.

The polyphenols, fibre, protein, and arginine that appear to drive these results are present in the whole food as it grows. That’s worth sitting with for a moment.

If you’re curious about what else plant-based eating can do for your health, there’s a gentle starting point over on our guide to getting started with a vegan lifestyle. No pressure. Just the information, and a jar of peanut butter if you happen to have one around.