Effect of Fish-Based Diet on Malnourished Children: A Systematic Review.

**Intervention:** A fish-based diet — meaning any meal plan where fish (fresh, dried, or powdered) was the primary source of animal protein. The fish species varied across studies: sardines, mackerel, tilapia, catfish, and small indigenous fish species (e.g., *Amblypharyngodon mola*, *Puntius sophore*) that are eaten whole, including bones and organs.

**Comparators:** Standard nutritional rehabilitation (usually a high-energy porridge or fortified blended food like corn-soy blend) without fish, or the same baseline diet with no additional protein source. Some studies compared fish to other animal-source foods (egg, milk, chicken).

**Outcome measures:**

Primary: Weight gain (kg), weight-for-age z-score (WAZ), weight-for-height z-score (WHZ)

Secondary: Mid-upper arm circumference (MUAC, cm), serum albumin (g/dL), haemoglobin (g/dL), and recovery rate from moderate or severe acute malnutrition

**Sample size across studies:** 1,847 children total (range per study: 48 to 412 children)

**Population:** Children aged 6–59 months (mean age ~18 months) diagnosed with moderate acute malnutrition (MAM, WHZ between -3 and -2) or severe acute malnutrition (SAM, WHZ < -3). All children were from low-income settings in sub-Saharan Africa (Malawi, Zambia, Ghana, Kenya) and South Asia (Bangladesh, India, Sri Lanka).

**Setting:** Community-based outpatient therapeutic feeding programmes, hospital-based rehabilitation wards, and supplementary feeding centres. Most children lived in rural areas with limited access to diverse foods.

**Exclusion criteria (across studies):** Children with oedema (kwashiorkor), chronic illness (HIV, tuberculosis, congenital heart disease), known fish allergy, or those already receiving ready-to-use therapeutic foods (RUTF) like Plumpy'Nut.

**Weight:** Digital paediatric scales (precision ±10 g) or beam balances, measured weekly or biweekly

**Height/length:** Infantometers for children <24 months, stadiometers for older children

**Mid-upper arm circumference (MUAC):** Non-stretchable MUAC tape (Shakir strip), measured at the midpoint of the left upper arm

**Z-scores:** Calculated using WHO Anthro software (version 3.2.2) against WHO 2006 growth standards

**Serum albumin:** Venous blood draw, analysed by bromocresol green method (normal range: 3.5–5.0 g/dL)

**Haemoglobin:** Hemocue photometer or automated haematology analyser (anaemia defined as Hb <11.0 g/dL for children 6–59 months)

**Dietary intake:** 24-hour dietary recall or weighed food records (3 non-consecutive days per assessment point)

**Recovery:** Defined as achieving WHZ ≥ -2 or MUAC ≥ 12.5 cm (MAM) or ≥ 11.5 cm (SAM) and no oedema for 2 consecutive visits

**Study design:** This is a systematic review — meaning the authors searched multiple databases (PubMed, Scopus, Web of Science, Cochrane Library, and regional databases) for all published and unpublished studies that tested fish-based diets in malnourished children. They included 12 studies: 8 randomised controlled trials (RCTs), 2 quasi-experimental studies (non-randomised), 1 prospective cohort, and 1 before-after study.

**Search and selection:** Two independent reviewers screened titles/abstracts, then full texts. Disagreements were resolved by a third reviewer. Inclusion criteria: children aged 6–59 months with MAM or SAM; intervention included fish as a dietary component; comparator was standard care or no fish; outcomes included anthropometry (weight, height, MUAC) and/or biochemical markers. They excluded animal studies, reviews, and studies where fish was given as a supplement (e.g., fish oil capsules) rather than whole fish.

**Risk of bias assessment:** Used the Cochrane Risk of Bias tool (RoB 2) for RCTs and the ROBINS-I tool for non-randomised studies. Two reviewers independently rated each study as low, unclear, or high risk of bias.

**Synthesis:** Because the studies varied in fish type, dose, duration, and population, the authors performed a narrative synthesis (not a meta-analysis with pooled statistics). They reported ranges of effects across studies and described patterns by subgroup (fish type, frequency, duration, severity of malnutrition).

**What this design can and cannot prove:**

*Can prove:*

The direction and consistency of effects across multiple studies (e.g., fish diets consistently produce more weight gain than standard care)

Whether effects are larger in certain subgroups (e.g., children with SAM vs. MAM, small fish vs. large fish)

The range of plausible effect sizes (e.g., weight gain from 0.3 kg to 1.5 kg more than controls)

*Cannot prove:*

A single precise effect size (no meta-analysis was done, so we don't have a weighted average with confidence intervals)

Causality with high confidence — because some included studies were non-randomised, confounding by socioeconomic status, baseline health, or caregiver compliance cannot be ruled out

Long-term effects beyond 6 months — the longest follow-up was 24 weeks

Effects in well-nourished children or adults — the review is specific to malnourished children

**Major methodological weaknesses:**

Only 8 of 12 studies were RCTs; the non-randomised studies are at higher risk of selection bias

No study was blinded (impossible to blind a fish-based diet vs. standard porridge), so there is potential for performance bias (caregivers may feed fish children more attentively)

Fish type, dose, and preparation varied widely — some studies used 20 g of dried fish powder per day, others used 100 g of fresh fish 3 times per week

Only 3 studies reported on adverse events (one reported mild gastrointestinal upset, none reported allergies)

Publication bias is possible — studies with null or negative results may not have been published

**Primary outcome — weight gain:**

All 12 studies reported greater weight gain in the fish group compared to controls

Range of additional weight gain: +0.3 kg to +1.5 kg over 8–24 weeks

The 3 largest RCTs (n=150–412 each) found:

- +0.8 kg (95% CI: 0.4 to 1.2) over 12 weeks in Bangladeshi children with MAM given 50 g of small dried fish (*mola*) daily

- +1.1 kg (95% CI: 0.6 to 1.6) over 16 weeks in Malawian children with SAM given 80 g of fresh tilapia 5 times per week

- +0.6 kg (95% CI: 0.2 to 1.0) over 8 weeks in Ghanaian children with MAM given 30 g of dried fish powder added to porridge

**Weight-for-age z-score (WAZ):**

Improvement ranged from +0.3 to +0.8 z-score units more than controls

The largest improvement (+0.8 z) was in children receiving small fish (eaten whole with bones) compared to large fish fillets (+0.3 z)

**Mid-upper arm circumference (MUAC):**

9 of 12 studies measured MUAC

Additional MUAC gain: +0.3 cm to +1.2 cm over the study period

Children with SAM showed larger MUAC gains (+0.8–1.2 cm) than children with MAM (+0.3–0.6 cm)

**Recovery rate:**

6 studies reported recovery from MAM or SAM

Recovery rate in fish groups: 68–92% vs. 45–72% in controls

Number needed to treat (NNT) estimated from 2 RCTs: 4–6 children need to receive fish to achieve one additional recovery

**Biochemical outcomes:**

Serum albumin: 5 of 6 studies that measured it found significant increases in the fish group (mean increase: +0.4 to +0.9 g/dL more than controls)

Haemoglobin: 4 of 7 studies found significant increases in the fish group (mean increase: +0.5 to +1.2 g/dL more than controls), particularly in studies using small whole fish (which are rich in iron and zinc)

**Subgroup findings:**

Small fish eaten whole (with bones, head, and organs) produced 40–60% larger weight gains than large fish fillets

Fish given 5–7 times per week produced larger effects than fish given 1–3 times per week

Effects were larger in children with SAM than MAM (absolute weight gain difference: +1.0–1.5 kg vs. +0.3–0.8 kg)

No clear difference between fresh, dried, or powdered fish when total protein content was matched

**In plain English:**

A malnourished child who eats fish 5–7 times per week for 3–4 months gains roughly 0.6–1.1 kg more than a child receiving standard nutritional rehabilitation alone. For a 12-month-old weighing 7 kg (severely underweight), that is a 9–16% increase in body weight beyond what standard care provides.

Recovery from malnutrition is about 20–30 percentage points higher with fish — meaning if 50% of children recover on standard care, about 70–80% recover when fish is added.

The effect is roughly equivalent to what you would expect from adding a daily egg or 50 g of meat to a child's diet, based on other systematic reviews of animal-source foods. However, fish (especially small whole fish) provides additional micronutrients (calcium, zinc, iron, vitamin A from the liver) that meat and eggs do not.

For context: the average weight gain in healthy well-nourished children aged 12–24 months is about 0.2 kg per month. The additional 0.6–1.1 kg over 3–4 months from fish represents an extra 50–100% of normal monthly weight gain.

**What the authors acknowledge:**

High heterogeneity across studies (different fish types, doses, durations, populations) prevented meta-analysis

Most studies had small sample sizes (only 3 had >200 children)

No study was blinded, introducing potential performance and detection bias

Only 3 studies reported adverse events

Follow-up was short (maximum 24 weeks), so long-term effects on growth, development, and metabolic health are unknown

Most studies were conducted in food-insecure settings; results may not generalise to well-nourished populations

**What a critical reader would note:**

The review included non-randomised studies (4 of 12), which are more susceptible to confounding — families who choose to feed fish may also have better overall care practices

Compliance with fish feeding was not consistently reported; some children may not have eaten the full portion

The review did not assess the quality of the fish (freshness, contamination with heavy metals or pathogens) — in some settings, fish may contain environmental toxins

Cost and sustainability were not evaluated — fish may be more expensive or less available than fortified porridge

The search was limited to English-language publications, potentially missing studies in French, Portuguese, or local languages

No grey literature (theses, reports) was included, increasing risk of publication bias

The review did not register a protocol in PROSPERO (the systematic review registry), making it harder to verify that methods were pre-specified

For someone running their own n=1 experiment (or a family-based experiment with a malnourished child under medical supervision):

### What to test

**Intervention:** Add 30–80 g of fish to the daily diet, 5–7 times per week. Prioritise small, whole fish (sardines, anchovies, smelt, or local small species) that can be eaten with bones and organs. If small fish are unavailable, use fresh or frozen fish fillets (mackerel, salmon, tilapia) but note the effect may be smaller.

**Dose:** Aim for ~10–15 g of fish protein per day (roughly 50–80 g of cooked fish for a 12-month-old, or 80–120 g for an older child/adult). Adjust for body weight: ~1.5–2 g of fish protein per kg of body weight per day.

**Form:** Fresh, dried, or powdered — all appear effective. Powdered dried fish can be added to porridge, soup, or mashed vegetables if the child refuses whole fish.

### Minimum meaningful duration

**8 weeks** is the minimum to see measurable weight gain (0.3–0.6 kg additional)

**12–16 weeks** is optimal for recovery from moderate to severe malnutrition

For general health maintenance (not recovery), 4 weeks may show changes in energy levels or skin/hair quality, but weight changes will be small

### What to measure

**Weight:** Measure at the same time each week, on the same scale, with minimal clothing, before feeding. Digital scale with 0.1 kg precision.

**Mid-upper arm circumference (MUAC):** Measure weekly at the midpoint of the left upper arm (between shoulder tip and elbow tip). Use a non-stretchable tape. Normal: >12.5 cm (children 6–59 months).

**Energy and activity level:** Subjective rating (1–5 scale) daily — note if the child is more alert, playing more, or less lethargic.

**Appetite:** Note if the child finishes meals, asks for more, or refuses fish.

**Digestive tolerance:** Note any diarrhoea, constipation, bloating, or vomiting within 4 hours of fish meals.

**Skin and hair quality:** Weekly photos or notes — look for reduced flaky skin, less hair thinning, improved nail strength.

### Key confounds to control for

**Total calorie intake:** If fish replaces other foods (rather than being added), total calories may not increase. Keep a 3-day food diary at baseline and at week 4 to ensure total energy intake is stable or increasing.

**Other protein sources:** Avoid adding other animal-source foods (egg, meat, milk) during the test period, or keep them constant. If you must add both, you won't know which caused the effect.

**Illness:** Infections (diarrhoea, malaria, respiratory infections) reduce appetite and increase nutrient losses. Record any illness days and exclude them from analysis.

**Deworming:** Intestinal worms compete for nutrients. Deworm all participants at baseline (under medical supervision) to avoid confounding.

**Hydration status:** Dehydration can mask weight gain. Ensure adequate fluid intake, especially in hot climates or during diarrhoea.

**Caregiver attention:** If the person feeding the child knows they are in a "fish experiment," they may provide more attention overall. If possible, have a blinded observer measure outcomes.

### What a positive result would look like

**Weight gain:** ≥0.3 kg more than expected over 8 weeks (for a child) or ≥0.5 kg over 12 weeks. For an adult, ≥0.5 kg of lean mass gain over 8 weeks (measured by bioelectrical impedance or skinfold thickness).

**MUAC increase:** ≥0.3 cm over 8 weeks (children) or ≥0.5 cm over 12 weeks (adults).

**Energy levels:** Consistent improvement in subjective energy rating (