16.1 Food Consumption Surveys, Biochemical Tests in Surveys, and Clinical Signs of Deficiency
Key Takeaways
A single 24-hour recall estimates the mean intake of a group well, but several non-consecutive days per person are needed to estimate an individual's usual intake.
The EAR cut-point method estimates the prevalence of inadequate intake in a group as the proportion with usual intakes below the estimated average requirement.
WHO's 2024 cutoffs define anemia as hemoglobin below 105 g/L in children 6-23 months, below 110 g/L in children 24-59 months, below 120 g/L in non-pregnant women, and below 130 g/L in men.
A median urinary iodine of 100 µg/L or more indicates adequate iodine intake in school-age children, while pregnant women need a median of 150 µg/L or more.
Clinical signs of deficiency appear late and are often non-specific, so they should be confirmed with dietary and biochemical data.
The Community and Public Health Nutrition table of specifications asks examinees to explain food consumption survey methods, the objectives and limitations of dietary studies, the considerations in clinical and anthropometric assessment, biochemical tests used in surveys, and clinical signs of deficiencies.
Food Consumption Survey Methods
| Level | Method | Description | Strengths | Limitations |
|---|---|---|---|---|
| National | Food balance sheet | Food supply = production + imports - exports - stock changes - non-food uses, divided by population | Shows national trends; compares countries | Measures availability, not actual intake; no distribution data |
| Household | Food account | Household records all food entering the home over a period | Low burden per day | Misses food eaten away from home and waste |
| Household | Food inventory | Lists food stocks at the start and end of a period, plus purchases | Simple | Same limits as the food account |
| Household | Household food weighing | Weighs all food prepared and plate waste | Accurate for the household | Labor-intensive; may change behavior |
| Individual | 24-hour recall | Interviewer asks everything eaten the previous day, often using a multiple-pass method | Quick; low literacy needed; does not change behavior | Memory errors; one day does not show usual intake |
| Individual | Food record (weighed or estimated) | Respondent records foods as eaten for several days | Detailed; no memory reliance | High burden; people eat differently while recording |
| Individual | Food frequency questionnaire (FFQ) | How often foods are eaten over months | Ranks usual intake; useful for diet-disease studies | Poor for absolute intake; list must fit local foods |
| Individual | Diet history | Interview on usual pattern, often with a recall and an FFQ | Captures usual intake | Long interview; needs skilled staff |
FNRI national surveys have used household food weighing and individual 24-hour food recalls to estimate what Filipinos eat.
Objectives of dietary studies: describe food and nutrient intake, estimate the prevalence of inadequacy, identify groups at risk, examine diet-disease links, and evaluate programs.
Common sources of error:
- Underreporting, especially among people with obesity and of snacks and sweetened drinks
- Flat slope syndrome: low intakes over-reported and high intakes under-reported
- Portion size estimation errors; use food models, household measures, and photos
- Day-to-day variation: usual intake needs repeated days, especially for nutrients concentrated in a few foods, such as vitamin A
- Food composition table limits: missing local foods or outdated values (use the Philippine Food Composition Tables)
- Interviewer bias and seasonal differences
Evaluating Intake Against Standards
- For groups, compare usual intakes with the EAR: the proportion below the EAR estimates the prevalence of inadequacy (EAR cut-point method), when intakes are reasonably normally distributed and not for energy or iron in menstruating women.
- The REI or RNI is the target for individuals; intake at or above it has a low probability of inadequacy.
- Intakes above the UL suggest risk of excess.
- Energy adequacy is better judged by body weight and BMI than by reported intake.
Example. In a survey of 400 adolescent girls, 260 have usual calcium intakes below the EAR. The estimated prevalence of inadequate calcium intake is 260 ÷ 400 = 65%.
Biochemical Tests Used in Nutrition Surveys
| Nutrient | Indicator | Survey cutoff |
|---|---|---|
| Iron and anemia | Hemoglobin (WHO 2024 cutoffs) | Anemia below 105 g/L (children 6-23 months), 110 g/L (24-59 months), 115 g/L (5-11 years), 120 g/L (12-14 years, non-pregnant women), 130 g/L (men); in pregnancy below 110 g/L in the first and third trimesters and 105 g/L in the second |
| Iron stores | Serum ferritin | Below 12 µg/L in children under 5; below 15 µg/L in older people (adjusted for inflammation) |
| Vitamin A | Serum retinol | Below 0.70 µmol/L (about 20 µg/dL) indicates deficiency |
| Iodine | Median urinary iodine concentration | School-age: below 100 µg/L insufficient, 100 µg/L or more adequate, 300 µg/L or more excessive. Pregnant women: below 150 µg/L insufficient |
| Folate and B12 | Serum or red cell folate; serum B12 | Used in specialized surveys |
Public health significance of anemia (WHO): prevalence of 40% or more is severe, 20-39.9% moderate, and 5-19.9% mild. The 2023 NNS figure of 10.9% anemia among women of reproductive age is therefore a mild public health problem.
Public health significance of vitamin A deficiency: serum retinol below 0.70 µmol/L in 20% or more of preschool children is severe, 10% to under 20% moderate, and 2% to under 10% mild. A night blindness prevalence of 1% or more among children 24-71 months indicates a public health problem.
Considerations: biochemical tests are more objective and detect deficiency earlier than clinical signs, but they cost more, need cold chains and laboratories, can be affected by infection and inflammation (ferritin rises, retinol falls), and reflect recent intake for some nutrients.
Clinical Signs of Nutrient Deficiency
| Nutrient | Clinical signs |
|---|---|
| Vitamin A | Night blindness, Bitot's spots, conjunctival and corneal xerosis, keratomalacia, follicular hyperkeratosis |
| Thiamine | Beriberi: wet (edema, heart failure) or dry (neuropathy); Wernicke encephalopathy |
| Riboflavin | Angular stomatitis, cheilosis, magenta tongue |
| Niacin | Pellagra: dermatitis on sun-exposed skin (Casal's necklace), diarrhea, dementia |
| Vitamin C | Scurvy: swollen bleeding gums, perifollicular hemorrhages, corkscrew hairs, poor wound healing |
| Vitamin D | Rickets: bowed legs, rachitic rosary, frontal bossing, delayed fontanelle closure; osteomalacia in adults |
| Iron | Pallor, koilonychia (spoon nails), fatigue, glossitis |
| Iodine | Goiter; cretinism in severe deficiency during pregnancy |
| Protein-energy | Kwashiorkor (edema, flaky paint dermatosis, flag sign, moon face); marasmus (severe wasting, "old man" face) |
| Zinc | Growth retardation, delayed sexual maturation, poor wound healing, dermatitis, taste loss |
| Folate and B12 | Megaloblastic anemia, glossitis; neurologic signs with B12 deficiency |
Considerations in clinical and anthropometric assessment: clinical signs appear late and are non-specific (angular stomatitis also results from ill-fitting dentures and infection), and examiner judgment varies, so examiners need training and standard definitions. Anthropometry needs calibrated equipment, standardized technique, and accurate ages, and teams should check measurement reliability through repeated measurements.
A researcher wants to rank 2,000 adults by their usual intake of fried foods over the past year to study links with heart disease. Which method is most suitable?
A single 24-hour recall
A food balance sheet
A food frequency questionnaire
A household food inventory
In a survey of 500 pregnant women, 120 are anemic by the WHO trimester-specific hemoglobin cutoffs. How is the public health significance of anemia classified using WHO criteria?
Severe public health problem
No public health problem
Mild public health problem
Moderate public health problem
During a survey, a child shows foamy, triangular gray patches on the white of the eye. Which deficiency do these signs indicate?
Vitamin A deficiency
Riboflavin deficiency
Vitamin C deficiency
Iodine deficiency
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