In this study, the investigators will evaluate the efficacy, safety and related mechanism of dietary fiber and probiotics alone and in combination as a add-on treatment in improving the antipsychotic induced weight gain, the cognitive impairment, and psychotic syndrome in schizophrenia or bipolar disorder patients. The study will recruit 100 schizophrenia or bipolar disorder patients who meet the criteria of DSM-5, and then randomized to 4 groups: probiotics group(PB group) dietary fiber group(FB group) probiotics plus dietary fiber group(PF group) and control group(CT group) for a 12-weeks clinical trail. The specific aims are to compare probiotics group versus controls on: 1) clinical core symptoms; 2) cognition;3)metabolic related markers.

In this study, the investigators will evaluate the efficacy, safety and related mechanism of dietary fiber and probiotics alone and in combination as a add-on treatment in improving the antipsychotic induced weight gain, the cognitive impairment, and psychotic syndrome in schizophrenia or bipolar disorder patients. The study will recruit 100 schizophrenia or bipolar disorder patients who meet the criteria of DSM-5, and then randomized to 4 groups: probiotics group(PB group) dietary fiber group(FB group) probiotics plus dietary fiber group(PF group) and control group(CT group) for a 12-weeks clinical trail (20 patients per arm) for a 12-weeks clinical trail. Clinical efficacy and safety assessment will be done at screen/baseline, 4 week, 8 week and 12 week. The specific aims are to compare probiotics group versus controls on: 1) clinical core symptoms; 2) cognition; 3) metabolic related markers. Biological samples also will be collected, and stored to research related mechanisms. Clinical symptoms will be measured by the Positive and Negative Syndrome Scale,. Cognitive function will be assessed by the MATRICS Consensus Cognitive Battery.

The investigators hypothesize that: 1) dietary fiber and probiotics may improve cognitive impairment of patients with schizophrenia; 2) dietary fiber and probiotics could prevent the cognitive decline of patients with schizophrenia; 3)dietary fiber and probiotics may prevent the antipsychotics induced weight gain in patients with schizophrenia.4)dietary fiber and probiotics may alter oxidative stress indexes or inflammatory biomarkers thus influence the oxidative and inflammatory mechanism.

Inclusion Criteria:

1. Meet the Diagnostic and Statistical Manual (DSM-V) diagnostic criteria for schizophrenia or bipolar disorder;
2. Patients with a weight gain of more than 10% after taking antipsychotic medications;
3. Male and female with aged 18 to 65 years;
4. PANSS total score < 60 or HAMD-17 total score≤ 7 and YMRS total score<5;
5. Signed the study consent for participation;
6. Not allergy to probiotics or dietary fiber medicine
7. On stable medication and dosage for at least 3 months.

Exclusion Criteria:

1. Having history of substance dependence or abuse or whose symptoms are caused by the other diagnosable mental disorders;
2. Having history of traumatic brain injury, seizures or other known neurological or organic diseases of the central nervous system;
3. Taking antidepressants, stimulants, mood stabilizer or accepts electricity shock treatment;
4. Having current suicidal or homicidal thoughts or any safety concern by research staff that cannot be manage in an inpatient setting;
5. The routine blood tests showing abnormal renal, liver function;
6. Pregnant or lactating women.
7. No administration of any antibiotics in two mouths