Human health

Why do animal-sourced foods make it easier to meet protein targets?

The protein-to-carbohydrate ratio in a diet is associated with an enhanced supply of micronutrients and lower all-cause mortality. Nutritional adequacy also relies on protein quality, which is typically more favourable in animal-derived foods than in plants, based on the essential amino acid profiles and digestibility in the small intestine. To meet the essential amino acid needs adequately, plant-based diets may require higher protein amounts, and therefore also a higher intake of food and energy. This comes with practical challenges, especially in older adults. The recommended dietary allowance for protein has been estimated at 0.83 g per kg body weight per day, but may need to be revised to 1.0 g/kg based on new lines of evidence. Even higher protein intake seems to be beneficial for many if not most adults, with different optimal levels (1.2-2.2 g/kg) for specific groups like athletes, pregnant and lactating women, aging adults, and those with chronic diseases.

Protein as the cornerstone of a nourishing diet


High-income countries have greater access to animal source proteins compared to low- and middle-income countries, but this does not guarantee adequacy. The overall protein levels in the West are considered high, exceeding what is recommended. However, these recommendations may be too low and not universally optimal for all population groups. 

Moreover, the claim that high protein intake may harm bone and kidney health is disputed, emphasizing a remarkable evolutionary adaptation to elevated protein levels in modern humans.

Recommendations may be too low for many

The recommended dietary allowance (RDA) for protein is conventionally set at 0.83 g per kg of body weight, at population level. This is a minimum value to prevent loss of lean body mass in healthy adults, not an optimal one, and not even one reached by everyone. 

Re-analysis of nitrogen balance data and other evidence suggests that this target may be too low to begin with, as some of the evidence suggests that consuming below 1.3 g/kg/d could lead to muscle mass loss. Many individuals may benefit from even higher protein intake, as outlined below. 

Suggested optimal protein intakes vary per population


The suggested daily protein intake may need to be revised from 0.83 to >1.0 g per kg of bodyweight. Even higher amounts, by at least doubling the value, are advised for specific groups, including athletes, people wishing to reduce weight, pregnant and lactating women, older adults, and the diseased. 

These targets for optimal health are often not met. For instance, older adults in nursing homes tend to underconsume protein, while being less efficient at building or maintaining muscle mass.

Adequate protein as % of energy intake


Suitable protein intake depends on the overall diet. Instead of using a minimum RDA, protein needs can be expressed as a percentage of caloric intake. The recommended protein range is set at 10-35% of daily energy intake. 

The higher end of this range, corresponding with ancestral-type hunter-gatherer diets, has shown health benefits, including an improvement in cardiometabolic risk factors.

Protein sources differ in nutritional value


Protein sources vary in nutritional value, and a simple mass-based comparison is inadequate. Animal-derived proteins offer better quality than plant proteins, with higher anabolic responses for skeletal muscle. For older adults, meat-based meals are more effective than vegetarian options. On average, vegetarian diets are associated with lower muscle mass and strength.

Plant-based strategies for muscle protein synthesis may need fortification or higher intake.  A recommended animal-to-plant protein ratio is 50:50, with a 40:60 ratio potentially suitable but more risky with respect to the adequacy of micronutrients. 

The True Ileal Digestibility (DIAAS) method is more accurate than PDCAAS for assessing protein value. Animal proteins have higher DIAAS values than most plant proteins. The Essential Amino Acid 9 (EAA-9) score, considering personalized requirements, provides an alternative for precision nutrition based on age or metabolic conditions.