Dietary Protein Requirements: Evidence, Controversies, and Food Sources in African Diets

The history of protein in global nutrition policy is, in no small measure, the history of a scientific overcorrection. For much of the mid-twentieth century, protein deficiency was regarded as the defining nutritional catastrophe of the post-colonial developing world - a condition so pervasive that a dedicated international effort, the Protein Advisory Group of the United Nations, was convened to address what was confidently called the “protein gap.” The clinical anchor of this alarm was kwashiorkor, the severe acute malnutrition syndrome first described systematically by Cicely Williams in 1935 in children presenting with oedema, skin lesions, and growth arrest following weaning. The name itself derives from the Ga language of coastal Ghana - meaning, roughly, “the sickness the child gets when displaced from the breast” - and the condition became the face of third-world malnutrition in the popular and scientific imagination alike.

What followed was a significant intellectual reversal. By the late 1970s, the protein gap hypothesis had been substantially dismantled. Revisionist analyses demonstrated that caloric insufficiency, not isolated protein deficiency, was the primary driver of most malnutrition observed in low-income settings; that improving caloric intake generally resolved apparent protein deficiency; and that the earlier emphasis on protein had distorted research funding and policy attention away from the more fundamental problem of energy scarcity. The pendulum swung hard: for a generation, protein received comparatively little dedicated attention in the global nutrition discourse.

That neglect has been replaced by a more careful and empirically grounded engagement with protein nutrition. Current evidence recognises that protein requirements interact with total energy intake, that protein quality - measured in terms of both amino acid composition and digestive availability - varies enormously across food sources, and that in many Sub-Saharan African (SSA) dietary contexts, the quantity and quality of dietary protein available to children and adults alike may be insufficient to support optimal health, growth, and productivity. This article examines that evidence, from the WHO/FAO recommendations through to contemporary debates about plant and animal protein, legumes, cereals, insect protein, and the implications of food system constraints for nutrition policy. For the broader context of food system adequacy, the comparative analysis of food security provides essential structural background; for the consequences of inadequate nutrition across the life course, the overview of malnutrition definitions, types, and causes is directly relevant.

The WHO/FAO Recommended Dietary Allowance for Protein

The current international reference standard for adult protein requirements derives from the 2007 joint report of the World Health Organisation, the Food and Agriculture Organisation, and the United Nations University on protein and amino acid requirements in human nutrition (WHO/FAO/UNU, 2007). This report, which superseded the 1985 joint expert consultation, applied a factorial modelling approach combined with nitrogen balance methodology and stable isotope tracer studies to derive both average requirements and population reference intakes.

The safe level of protein intake - equivalent to the recommended dietary allowance - was set at 0.83 g of protein per kilogram of body weight per day for healthy adults under conditions of adequate energy intake. This figure applies to protein of high quality and high digestibility; where dietary protein comes predominantly from sources with lower digestibility or incomplete amino acid profiles, the effective requirement is higher. The population reference intake is set two standard deviations above the average requirement, reflecting inter-individual variation in nitrogen metabolism.

These recommendations have attracted sustained methodological criticism. The nitrogen balance technique - which assesses the equilibrium between dietary nitrogen intake and urinary, faecal, and dermal nitrogen losses - has been argued to systematically underestimate true requirements by several mechanisms: subjects may adaptively suppress nitrogen excretion during short-term feeding trials, and the test conditions of metabolic ward studies do not replicate the physical activity levels and dietary variety of free-living individuals. Tracer-based indicator amino acid oxidation (IAAO) studies have generated somewhat higher estimates, suggesting that the 0.83 g/kg/day figure may understate requirements, particularly for older adults and physically active populations (WHO/FAO/UNU, 2007).

For pregnant and lactating women, requirements are substantially elevated. The 2007 report recommended an additional 1 g/day in the first trimester, 9 g/day in the second trimester, and 31 g/day in the third trimester - figures carrying direct relevance for SSA populations where maternal dietary protein intakes are frequently inadequate during gestation.

Protein Quality: PDCAAS and the Move to DIAAS

Knowing how much protein a person needs is necessary but insufficient without a method for quantifying how much of the protein in a given food is actually available to meet those needs. The concept of protein quality captures both the amino acid composition of a food - whether it provides all nine indispensable amino acids in adequate proportions - and the digestive availability of those amino acids. Two scoring systems have been used to operationalise this concept.

The Protein Digestibility-Corrected Amino Acid Score (PDCAAS), adopted by the FAO/WHO in 1991, was for two decades the dominant metric. PDCAAS is calculated as the ratio of the most limiting essential amino acid in a food relative to a reference amino acid pattern, multiplied by faecal protein digestibility. Scores are truncated at 1.0 (or 100%), meaning that foods with surpluses of essential amino acids above the reference pattern receive no additional credit. High-quality animal proteins - dairy, eggs, meat - typically achieve PDCAAS scores at or near the maximum; many plant proteins, particularly cereals, score substantially lower due to limitations in lysine and threonine.

Millward and colleagues identified several shortcomings of the PDCAAS framework.¹ Faecal digestibility captures ileal amino acid absorption imperfectly, since nitrogen that reaches the faeces includes both unabsorbed dietary nitrogen and endogenous secretions; true ileal digestibility - the proportion of dietary amino acid absorbed before the terminal ileum - is a more accurate measure of bioavailability. The truncation rule was also criticised for concealing the genuine amino acid surplus of high-quality proteins and distorting comparisons.

The Digestible Indispensable Amino Acid Score (DIAAS), proposed by an FAO expert consultation and detailed by Tome in the peer-reviewed literature, addresses these shortcomings by using ileal digestibility values measured in either humans or pigs as proxy species, and by eliminating the truncation rule.² DIAAS is calculated as the ratio of each digestible indispensable amino acid in the food to the same amino acid in the reference pattern, with the lowest ratio - the most limiting amino acid - defining the score. DIAAS values greater than 100 are possible and meaningful, as they indicate that the food provides more than the reference requirement of all indispensable amino acids on a per-100 g protein basis.

The practical implication of the DIAAS framework is to sharpen the distinction between high-quality protein sources and those that require dietary complementation. Whole eggs achieve a DIAAS of approximately 113; whole milk approximately 114; beef approximately 111. Chickpeas score around 83; refined wheat around 42; corn around 44. The gap between plant and animal protein quality, already visible under PDCAAS, becomes more pronounced under DIAAS, with important implications for populations whose protein supply is predominantly plant-based.

Plant Versus Animal Protein: Biological and Practical Dimensions

The distinction between plant and animal protein quality carries substantial implications for dietary adequacy in SSA, where animal-source foods - meat, dairy, eggs, fish - are frequently unaffordable, unavailable, or culturally restricted for segments of the population. Van Vliet and colleagues provided a thorough analysis of the anabolic response to plant and animal proteins, demonstrating that the lower leucine content and reduced digestibility of most plant proteins attenuates muscle protein synthesis rates compared to equivalent doses of animal protein.³ This finding has practical significance for elderly adults and for populations engaged in high physical labour, where muscle mass maintenance and repair are ongoing requirements.

At the same time, it is essential to avoid overstating the practical significance of in vitro and single-meal amino acid studies for whole-diet outcomes. When plant proteins are consumed in mixed diets and in adequate total quantities, the concept of dietary complementarity - combining protein sources with complementary amino acid profiles - substantially mitigates the limitations of any individual food. The pairing of cereal and legume foods, widely practised in SSA traditional diets (e.g., maize and cowpea in West Africa, injera and lentil stew in Ethiopia, ugali and beans in East Africa), improves the amino acid profile of the combined meal considerably relative to either component alone.

The challenge in SSA is not, therefore, simply one of protein quality in isolation, but of whether the complementary combinations are present in adequate quantities, whether the energy density of the overall diet is sufficient to spare amino acids from catabolism for fuel, and whether individual household food security permits the dietary diversity necessary to achieve complementarity reliably across seasons. Alexandratos and Bruinsma’s FAO projections for world agriculture through 2030 and 2050 emphasise that growth in animal-source food demand in Sub-Saharan Africa is projected to be among the most rapid globally, driven by demographic expansion and rising incomes - a structural shift with profound implications for land use, water resources, and the environmental sustainability of regional food systems.⁴

Legumes: The Central Plant Protein Source in SSA

Legumes - pulses including cowpea, common bean, lentil, groundnut, and soybean - occupy a uniquely important position in the protein landscape of Sub-Saharan Africa. They are the primary plant-based source of lysine, the amino acid most limiting in cereal-dominated diets; they provide meaningful quantities of iron, zinc, and B vitamins; and in most SSA settings they are substantially more affordable per unit of protein than meat or dairy. Their agronomic properties - nitrogen fixation from atmospheric sources via root symbionts - make them doubly valuable by improving soil fertility and reducing dependence on synthetic fertilisers that many smallholder farmers cannot afford.

Cowpea (Vigna unguiculata) is among the most drought-tolerant food legumes, making it critical for semi-arid zones across the West African Sahel, where it represents the dominant pulse crop. Common bean (Phaseolus vulgaris) is the principal legume across much of East and Central Africa. Groundnut, though technically an oilseed, provides substantial protein and is consumed widely across the continent both as a food and a processing crop.

Bouis and Saltzman, writing on biofortification as a strategy to improve the nutritional quality of staple crops, highlighted legumes as priority targets for genetic improvement - particularly for enhancing iron and zinc content, where both crop breeding and mineral bioavailability represent simultaneous constraints.⁵ Groundnut and common bean biofortification programmes under HarvestPlus have produced high-iron bean varieties achieving approximately 50–100% higher iron concentrations than conventional varieties, with evidence from efficacy trials in Rwanda and Democratic Republic of Congo that consumption of biofortified beans improves iron status in women and children.

Anti-nutritional factors in legumes - phytates, polyphenols, trypsin inhibitors - reduce the bioavailability of protein and micronutrients, and this is a genuine constraint on the nutritional value of raw or minimally processed pulses. Traditional processing methods, including soaking, fermentation, and germination, are well-documented to reduce phytate concentrations and improve protein digestibility substantially. The extent to which these practices are routinely applied, however, varies by household, season, and access to processing facilities.

Cereals and the Lysine Constraint

Maize, sorghum, millet, and wheat together provide the bulk of energy in most SSA diets, and therefore also contribute substantially to protein intake in absolute terms, even though their protein quality as measured by DIAAS is low. Maize protein is severely limited by lysine and tryptophan; sorghum and millet by lysine; wheat by lysine but with relatively higher threonine compared to maize. When energy intake is high, the sheer volume of cereal consumption can provide adequate absolute lysine if complementary sources are also present - but in energy-deficient settings, where protein is being catabolised for fuel, the quality constraint becomes compounding.

Quality Protein Maize (QPM), developed through conventional plant breeding and carrying the opaque-2 gene modification that nearly doubles lysine and tryptophan concentrations, represents one engineered solution. QPM varieties have been deployed in Ethiopia, Ghana, Nigeria, Zambia, and Tanzania, and randomised feeding trials have demonstrated improved growth outcomes in children consuming QPM compared to controls receiving conventional maize. Implementation challenges - including farmer adoption rates, seed system limitations, and the sensory properties of QPM flour - have constrained scale-up.

Insect Protein: An Emerging Contribution

Edible insects represent a protein source that is culturally familiar and actively consumed in numerous SSA contexts, though their integration into formal nutrition policy remains nascent. Termites, grasshoppers, caterpillars, crickets, and various beetle larvae are consumed across West, Central, and East Africa, both as snack foods and as ingredients in cooked dishes. Their protein content is substantial - dried crickets contain between 50–70% protein by dry weight - and the amino acid profiles of many edible insect species compare favourably with conventional animal-source foods.

Insect protein also offers advantages from environmental sustainability and production efficiency perspectives. Feed conversion ratios for crickets are approximately two-fold more efficient than poultry and six-fold more efficient than beef; insects can be reared on organic waste streams; and their land and water footprints are substantially lower than those of equivalent protein production from conventional livestock. These properties have generated significant policy and investment interest in insect farming across SSA, with enterprises in Kenya, Uganda, Ghana, and Côte d’Ivoire scaling production.

Black and colleagues’ Lancet series on maternal and child undernutrition identified dietary diversity - including access to animal-source foods - as a critical mediator of adequate child growth, and insect protein may represent one practically achievable pathway to increasing dietary protein quality and micronutrient density in SSA without requiring the resource-intensive infrastructure of conventional livestock systems.⁶

Protein Adequacy in Typical SSA Diets: What the Evidence Shows

Aggregate dietary data for Sub-Saharan Africa suggest that the region as a whole approaches recommended protein quantities in terms of grams per capita per day, but that this aggregate conceals important inequalities by age, sex, wealth quintile, and seasonality. Bhutta and colleagues documented that inadequate dietary intake of protein and key micronutrients - particularly zinc and iron - was among the proximate determinants of the growth faltering and developmental impairment observed across high-burden SSA settings.⁷

Critically, the age group with the highest protein quality requirements relative to intake is young children aged 6–24 months, during complementary feeding. The complementary foods most commonly offered in SSA settings - thin gruels made from maize, cassava, or millet flour - are energy-dilute, protein-poor, and limited in amino acid quality. The gap between what these gruels provide and what the growing child requires is one of the most important nutritional deficits in the region, and its consequences - faltered linear growth, impaired cognitive development - are well-documented across the stunting literature.

For adults, the dietary evidence suggests that marginal protein inadequacy may be common during agricultural lean seasons, when household food stocks are depleted and dietary diversity is at its nadir. Seasonal variation in dietary protein intake has been documented across Sahelian West Africa and the Great Lakes region, with lean season intakes falling meaningfully below safe levels in the lowest-income households. These seasonal dynamics are often invisible in cross-sectional survey data collected at single time points.

Food Security Policy Implications

The foregoing analysis carries several implications for food security policy in Sub-Saharan Africa that deserve explicit articulation. First, dietary protein adequacy is not separable from energy adequacy: interventions that improve caloric availability reliably also improve effective protein utilisation. Second, the emphasis on plant protein quality - particularly through legume promotion, biofortification, and traditional processing - represents a high-value, affordable pathway to protein quality improvement that does not require the scaling of animal agriculture. Third, insect protein deserves integration into national dietary guidelines and food systems strategies, given the growing evidence base for its nutritional value and the cultural acceptance in many settings.

Bouis and Saltzman’s work on biofortification further reinforces the importance of crop-based solutions: improving the amino acid composition, micronutrient density, and bioavailability of staple crops that already dominate SSA diets is a structurally more robust strategy, for most households, than attempting to shift dietary composition through increased animal-source food access alone.⁵ Both pathways have merit and should be pursued in parallel, rather than presented as alternatives.

Limitations

Several limitations circumscribe the conclusions drawn in this review. The DIAAS values cited for specific foods derive largely from studies conducted in high-income country settings using Western breeds of pigs or human ileostomy subjects; the extent to which these digestibility coefficients apply accurately to partially processed or fermented forms of the same foods as consumed in SSA contexts is uncertain. Anti-nutritional factor concentrations, processing methods, and gut microbiome composition all influence in vivo digestibility in ways that laboratory measurements may not fully capture.

The aggregate dietary adequacy data for SSA cited above derive from FAO Food Balance Sheets, which represent national food supply rather than individual household intake; household and intra-household distribution inequalities mean that per capita averages systematically overstate the intake of the most nutritionally vulnerable subgroups - women, young children, and the poorest households. Seasonality effects are similarly attenuated in annual averages.

Evidence on insect protein digestibility and amino acid bioavailability in humans remains limited compared to conventional foods; most data derive from in vitro analyses or animal studies rather than human feeding trials. Caution is warranted in extrapolating laboratory assessments to habitual dietary contributions.

Frequently Asked Questions

What is the recommended daily protein intake for adults, and does it differ across Sub-Saharan Africa? The WHO/FAO safe level of protein intake for healthy adults is 0.83 g per kilogram of body weight per day, applicable where dietary protein is of high digestibility and adequate amino acid composition. In practice, this figure should be adjusted upward where dietary protein is predominantly from low-digestibility plant sources - as is common in many SSA settings - to account for reduced amino acid bioavailability. Pregnant and lactating women have substantially higher requirements. There is no evidence that genetic differences across African populations alter basal protein requirements, but physical activity levels, disease burden, and infectious illness - all elevated in many SSA settings - increase protein turnover and may raise effective requirements modestly above population reference values.

Can plant-based diets in Sub-Saharan Africa provide adequate protein without animal-source foods? Adequacy is achievable but not automatic. Mixed plant-based diets that combine complementary protein sources - particularly cereals with legumes - can supply all essential amino acids in adequate quantities when total food intake is sufficient. The practical challenges are: ensuring that legume consumption is consistent across seasons; applying traditional processing methods that reduce anti-nutritional factors; and maintaining adequate total energy intake so that dietary protein is spared from catabolism for fuel. For young children during complementary feeding, the energy and nutrient density constraints of typical plant-based gruels make achieving adequate protein quality genuinely difficult without targeted intervention.

What makes insect protein nutritionally valuable compared to conventional protein sources? Edible insects consumed in SSA are notable for high protein concentration (50–70% of dry weight in species such as crickets and termites), favourable amino acid profiles approaching those of conventional animal proteins, and meaningful micronutrient contributions - particularly iron, zinc, and B12. Their DIAAS values vary by species and preparation method but are generally competitive with legumes and in some cases approach those of conventional meats. The environmental efficiency arguments, while not strictly nutritional, reinforce the case for insect protein as a component of sustainable food systems in resource-constrained settings.

Why did the protein gap hypothesis fall out of favour, and what has replaced it? The protein gap hypothesis was dismantled principally on the grounds that it conflated energy deficiency with protein-specific deficiency. Most of the malnutrition attributed to protein inadequacy in the 1960s was reconceptualised as primarily a consequence of insufficient total dietary energy, and the observation that adequate energy intake generally resolved apparent protein deficiency without specific protein supplementation was taken as decisive evidence. Contemporary nutritional science does not deny the existence of protein requirements or their practical relevance, but places protein quality within a broader nutritional systems framework that foregrounds energy adequacy, dietary diversity, micronutrient sufficiency, and food system access as jointly necessary conditions for adequate nutritional status.