Could This Fibre Improve Memory And Sleep

Can a Prebiotic Fibre Improve Memory and Sleep in Older Adults? What a 2024 Clinical Trial Found

If you’re over 60 and looking for evidence-based ways to protect your cognitive health, a recently published clinical trial has some genuinely interesting findings — centred on a little-known prebiotic fibre called Partially Hydrolyzed Guar Gum (PHGG).

Published in April 2024 in the peer-reviewed journal Nutrients, this randomised, double-blind, placebo-controlled trial examined whether daily supplementation with PHGG could improve cognitive function, sleep quality, and mood in healthy elderly individuals. The results suggest it can — particularly for visual memory and sleep clarity.

Here’s a full breakdown of what the research found, why it might work, and what it could mean for you.

What Is PHGG (Partially Hydrolyzed Guar Gum)?

Partially Hydrolyzed Guar Gum is a water-soluble prebiotic dietary fibre derived from guar beans, which are grown in arid regions including India and Pakistan. It is produced by partially breaking down the high-viscosity gum found in guar bean seeds, resulting in a fine, tasteless, odourless powder that dissolves easily in water or food.

PHGG is classified as a prebiotic — meaning it acts as a food source for beneficial gut bacteria, rather than being a probiotic (live bacteria) itself. It has been extensively studied for its effects on gut health, including improving bowel regularity, alleviating diarrhoea, and increasing populations of beneficial bacteria such as Bifidobacterium and butyrate-producing bacteria.

What makes PHGG particularly interesting from a brain health perspective is its high fermentability. When gut bacteria ferment PHGG, they produce short-chain fatty acids (SCFAs) — compounds that play a critical role in the gut-brain axis.

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The Gut-Brain Axis: Why What Happens in Your Gut Matters to Your Brain

The gut-brain axis is the bidirectional communication network between your gastrointestinal system and your central nervous system. This isn’t just a metaphor — it’s a real, physical system involving the vagus nerve, the immune system, the endocrine system, and microbial metabolites.

Gut bacteria produce a range of metabolites, including SCFAs, secondary bile acids, amino acid derivatives, and neurotransmitter precursors. These compounds can cross into the bloodstream, influence immune function, regulate inflammation, and directly affect brain activity.

Disruptions to the gut microbiome — sometimes called gut dysbiosis — have been increasingly linked to cognitive decline, depression, poor sleep, and even neurodegenerative diseases. Conversely, improving gut health through dietary interventions, including prebiotics and probiotics, has shown promise in supporting cognitive function, mood, and sleep quality in multiple clinical trials.

This is the framework within which the PHGG research sits.

About the Study: Design and Participants

The study was conducted between December 2022 and March 2023 at two clinics in Tokyo, Japan. It followed a rigorous randomised, double-blind, placebo-controlled, parallel-group design — considered the gold standard in clinical research. Participants and investigators alike were unaware of group assignments until the study was complete.

Who participated:

• 61 healthy Japanese adults aged 60 and over (30 in the PHGG group, 31 in the placebo group)
• All participants had a Mini Mental State Examination (MMSE) score of 24 or higher, indicating normal to good baseline cognitive function
• Participants had no history of major chronic illnesses and were not taking medications or supplements

What they took:

• PHGG group: 5 grams per day of PHGG (Sunfiber®), dissolved in water and taken with breakfast
• Placebo group: 5 grams per day of maltodextrin (a neutral carbohydrate with no prebiotic properties)

How long:

• 12 weeks, with assessments at baseline, 8 weeks, and 12 weeks

What was measured:

• Cognitive function using the Cognitrax computerised neurocognitive test
• Sleep quality using the OSA-MA (Oguri-Shirakawa-Azumi Sleep Inventory)
• Mood using the POMS-2 (Profile of Mood States, 2nd Edition)

Importantly, the two groups were well-matched at baseline — no significant differences in age, weight, BMI, blood pressure, or MMSE scores. This strengthens the reliability of any differences observed during the trial.

Key Finding #1: Visual Memory Significantly Improved

The primary outcome of the study was cognitive function, assessed using the Cognitrax test — a comprehensive, computerised battery that evaluates ten cognitive domains including verbal memory, visual memory, processing speed, executive function, and sustained attention.

Scores are standardised against age-matched norms, with 100 representing the average for a person’s age group.

What the data showed:

By week 12, the PHGG group demonstrated significantly higher visual memory scores compared to the placebo group. The change from baseline was also significantly greater in the PHGG group (+3.1 points) compared to the placebo group, which actually declined slightly.

In simple terms: while the placebo group’s visual memory scores drifted downward over 12 weeks, the PHGG group’s scores moved upward — and the gap between the two groups was statistically significant.

Why does visual memory matter?

Visual memory is your ability to retain and recall visual information — shapes, images, layouts, faces, written instructions. It underpins a wide range of daily activities: remembering where you parked, following graphical instructions, navigating routes, operating devices, and recognising people. It is considered a crucial function for independent living.

The researchers noted that while both groups remained within the “average” range on the Cognitrax scale throughout the study, only the PHGG group moved closer to the age-group mean over the 12 weeks — suggesting a meaningful functional improvement.

On simple attention at 8 weeks:

The PHGG group also showed significantly better simple attention scores at the 8-week assessment (p = 0.020), though the authors note this result should be interpreted with caution due to relatively high variability in baseline scores between groups.

Key Finding #2: Sleep Quality Improved — Particularly Morning Alertness

Sleep quality was assessed using the OSA-MA questionnaire, a validated psychological scale that evaluates sleep experience upon waking. It covers five sub-domains: sleepiness on rising, initiation and maintenance of sleep, frequent dreaming, refreshing sleep, and sleep length.

What the data showed:

The PHGG group demonstrated significantly better scores for sleepiness on rising at 8 weeks compared to the placebo group, with a significantly larger improvement from baseline.

At 12 weeks, the PHGG group continued to show a trend toward improvement in this domain, though it fell just short of statistical significance.

Within the PHGG group, scores for both sleepiness on rising and initiation and maintenance of sleep improved significantly from baseline at both 8 and 12 weeks. In the placebo group, no such improvements were observed.

What does “sleepiness on rising” actually measure?

In the OSA-MA framework, sleepiness on rising is a composite measure reflecting mental clarity on waking, stress relief, concentration capacity, and reduced irritability. In practical terms, an improvement here means waking up feeling clearer, less groggy, and more mentally ready to engage with the day — something that tends to decline with age.

These results align with a previous clinical study by the same research team, in which PHGG intake significantly improved self-reported refreshment on waking and reduced fatigue on waking in healthy adults.

Key Finding #3: Mood and Vitality Showed Within-Group Improvements

Mood was assessed using POMS-2, a well-validated tool covering seven mood states: anger-hostility, confusion-bewilderment, depression-dejection, fatigue-inertia, tension-anxiety, vigour-activity, and friendliness.

What the data showed:

No statistically significant differences were observed between the PHGG and placebo groups on any POMS-2 subscale. However, within the PHGG group:

• Vigour-activity scores increased significantly from baseline to 8 weeks
• Confusion-bewilderment scores decreased significantly from baseline to 12 weeks

Neither of these changes was observed in the placebo group.

In the POMS-2 scoring system, higher vigour-activity scores indicate more energy and vitality, while lower confusion-bewilderment scores indicate reduced mental fog and disorientation. Both changes point in a positive direction for cognitive-emotional wellbeing.

The researchers suggest that the lack of significant between-group differences may reflect high individual variability in mood scoring, and that future studies with more tightly defined participant populations may reveal clearer effects.

Why Might PHGG Have These Effects? The Proposed Mechanisms

The biological plausibility of these findings rests on several interconnected pathways:

1. Short-Chain Fatty Acid (SCFA) Production

PHGG is highly fermentable by gut bacteria, which produce SCFAs — primarily butyrate, propionate, and acetate — during fermentation. SCFAs have well-documented neuroprotective properties. They strengthen the intestinal barrier, suppress systemic inflammation, enhance the integrity of the blood-brain barrier, regulate immune cell function, and inhibit neuroinflammation. All of these mechanisms are relevant to cognitive health.

2. Intestinal Barrier Function

PHGG has been shown to increase mucin and tight junction proteins in the gut lining, reducing the permeability that can allow inflammatory substances to enter the bloodstream. By limiting this bacterial translocation and toxin influx, PHGG may help reduce the chronic low-grade inflammation that is increasingly associated with cognitive decline.

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3. Neurotransmitter Regulation

Animal studies have shown that PHGG intake increases serotonin and dopamine levels in the brain — including in the hippocampus, a region central to memory formation. Both neurotransmitters are deeply involved in mood, sleep, learning, memory, and motivation.

4. BDNF and Cholinergic Function

In aging rat models, PHGG supplementation has been shown to increase brain-derived neurotrophic factor (BDNF) — a protein that promotes neuronal growth and regeneration — and choline acetyltransferase, an enzyme involved in acetylcholine synthesis. Acetylcholine is the primary neurotransmitter associated with learning and memory, and its deficiency is a hallmark of Alzheimer’s disease.

5. Antioxidant Activity

Oxidative stress is a key driver of cognitive aging. Animal research has shown that PHGG enhances antioxidant enzyme activity and reduces oxidative damage in the liver and hippocampus — suggesting a protective effect on brain tissue integrity.

Limitations to Consider

This is a promising study, but it has limitations worth acknowledging:

• Sample size: With 30–31 participants per group, the study was relatively small. Larger trials are needed to confirm these effects.
• Duration: Three months is a fairly short intervention window for studying cognitive outcomes, which typically change slowly over years.
• Subjective measures: While Cognitrax is a validated computerised assessment, sleep and mood were measured purely through self-reported questionnaires. Future studies incorporating objective sleep monitoring (such as polysomnography or actigraphy) would strengthen the findings.
• Population specificity: Participants were healthy Japanese adults over 60 with normal cognitive scores. Results may not apply to individuals with existing cognitive impairment, or to younger populations.
• Funding: The study was funded by Taiyo Kagaku Co., Ltd., the manufacturer of Sunfiber® PHGG. Several authors are employed by the same company. This is a relevant disclosure, though the study design was rigorous and the data transparent.

What This Means in Practice

If you are in midlife or older and interested in supporting your cognitive health through diet, PHGG is a reasonably well-evidenced prebiotic fibre worth considering. It has a strong safety record, is well-tolerated, and has now been associated with improved visual memory and sleep quality in a controlled clinical trial.

The dose used in this study — 5 grams per day — is modest and equivalent to roughly one teaspoon of powder. PHGG dissolves completely in water, juice, or food without altering taste or texture, making it one of the more practical dietary supplements to incorporate daily.

PHGG is commercially available under the brand name Sunfiber® and as a generic ingredient in various supplement products.

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The Bottom Line

A well-designed 2024 randomised controlled trial found that 12 weeks of daily PHGG supplementation significantly improved visual memory and morning sleep quality in healthy adults aged 60 and over, compared to placebo. Within the PHGG group, vitality increased and mental fog decreased over the course of the study.

These effects are biologically plausible — PHGG supports gut health through SCFA production and microbiome modulation, which in turn influences brain function through the gut-brain axis.

While larger and longer studies are needed, this research adds meaningful evidence to the growing body of work suggesting that caring for your gut is one of the most powerful things you can do for your brain.

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This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before starting any new supplement.