Fiber Lifts Mood in Adults with Obesity

Dietary fiber improved mood and cholesterol in obesity

STUDY: Wang J et al, Nutrients 2026

STUDY TYPE: Randomized, double-blind, placebo-controlled trial

FUNDING: Independent

Background

The gut-brain axis has attracted growing interest as a target for mood disorders. In adults with obesity, disrupted gut microbiota may worsen both metabolic and psychological health. Dietary fiber acts as a prebiotic, feeding beneficial gut bacteria and generating short-chain fatty acids that signal to the brain. This trial tested whether fiber, probiotics, or the combination could improve metabolic markers, mood, and sleep.

The Study

• 55 adults with obesity (body fat >25% in men, >30% in women), age 30–45, in Taiwan.
• Randomized double-blind to placebo, dietary fiber (indigestible dextrin, 18 g/day), multi-strain probiotic capsule, or combined supplementation for 8 weeks.

Results

Dietary fiber improved total mood disturbance after statistical correction for multiple comparisons (effect size η²p = 0.168), with specifiic benefits for confusion, fatigue, anger, tension, and depression. Fiber also improved “good” (HDL) cholesterol (57.5 vs. 49.8 mg/dL).

Probiotics showed no significant effect on mood, sleep, or any metabolic marker after correction for multiple measures. Combining fiber and probiotics produced no additional benefit over fiber alone.

Limitations

Only 13–14 participants per group. Eight weeks is short. No microbiome or short-chain fatty acid measurements. Diet and physical activity weren’t monitored. Trial was retrospectively registered.

Practice Implications

• Is fiber really more effective than probiotics? Not if we look at the whole body of trials, but it makes sense to combine the two, and one trial found they worked better together for metabolic side effects of antipsychotics.
• Indigestible dextrin (the fiber used here) is available over the counter (18 g/day, such as Benefiber or Optifiber).
• The probiotics on this page have the strains that were tested in psych disorders, and include a prebiotic in the capsule (fiber is a type of prebiotic).