Evidence indicates that plant-based proteins have a lower anabolic effect than animal proteins, meaning that they yield lower muscle-building capacity per unit of protein. This is due to their less balanced essential amino acid content, which is often limiting in leucine and sulphur-containing amino acids. The food matrix also needs to be accounted for, as this defines protein digestibility (the protein quantity absorbed relative to the consumed amount). The latter depends on the protein structure, previous processing, and compounds limiting the digestion. Identifying an “optimal” protein source should therefore consider the characteristics of the protein and the food matrix in which it is consumed. Plant digestibility is reduced due to structural resistance, fibre, and anti-nutritional factors: phytates, tannins, trypsin inhibitors, and lectins, which can be partially attenuated through processing.
The better digestibility of animal proteins, and their more optimal amino acid composition, is reflected in the ileal digestibility scores for the dietary indispensable amino acids (DIAAS). These are typically higher than 1 in animal source foods, exceeding those of plant proteins (legumes: 0.6; cereals: 0.3-0.5), only approximated by soy (0.8-0.9). Based on these scores, plant foods like nuts, seeds, tofu, and pulses cannot claim to be a ‘good source’ of protein. Meeting the same protein target with plant options is certainly feasible, but comes with caloric intakes that are more elevated, often double or triple (even with beans and nuts). For example, to meet the same essential amino acid intake of 70 grams of meat with less than 80 kcal, we need two large portions of pasta with beans, with an energy intake of more than 700 kcal.
Paying sufficient attention to protein quality and quantity is not a luxury. There are important indications that protein-rich diets have favourable health outcomes, especially at the hormonal and metabolic level and in view of suppressing hunger. This happens above all in prediabetic and obese subjects, in which improvement of blood glucose, insulin sensitivity, inflammation, and lean body mass outcomes is seen. It is essential to have a good quality protein source as the centerpiece of a healthy eating pattern for all these reasons.
More information on protein can be found in a different section.
