A healthy diet is typically including a variety of minimally processed, plant-based foods (fruits, vegetables, nuts, whole grains, legumes, etc.) and moderate amounts of animal-based foods. Making healthy food choices to include more plant foods is worth applauding since a higher plant-based diet has consistently been associated with positive health outcomes. What percentage of animal foods shall we include in a healthy balanced diet?

    A recently published study assessed to what extent total proteins and animal protein contributions to total proteins could be theoretically reduced without impairing the fulfillment of all other nutrient-based recommendations (not including the use of nutritional supplements or fortified foods). The results from this study may help you to think about the balance between animal and plant food choices.

    Talking about protein, meat has higher protein content per kilocalorie than plant-based foods. More plant-based diets and less meat will inevitably reduce both total dietary proteins and animal protein contributions to total proteins. Animal proteins have a more balanced indispensable amino acid profile and greater digestibility than plant proteins. For the majority of people who are typically omnivorous and eating enough foods, the risk of inadequate protein intake is low, and it is minimally influenced by the animal protein contribution to the diet. The only caution is for elderly people because they have higher protein requirements than other adults (estimated at 1 g/kg for adults over 65 y and 0.83 g/kg for younger adults). If protein intake is lower than 1g/kg of body weight, the elderly may experience a higher risk of frailty.

    Protein-source foods provide several nutrients other than proteins and largely contribute to overall nutrient adequacy. Animal-based foods provide nutrients that are either not found in plant-based sources (such as vitamins D and B12 and long-chain omega 3 fatty acids), found in small amounts (e.g., vitamin B6 and riboflavin), or found in less bioavailable forms (e.g., iron and zinc). In addition, diets with plenty of plant-based foods are not necessarily more affordable than diets with more animal-based foods. Food budget constraints are important determinants of food choices, and healthy food choices tend to be more expensive than unhealthy ones.

    This published study used dietary data which were derived from the Second French Individual and National Study on Food Consumption, a 7- day open-ended food-record representative survey conducted between 2005 and 2007 by the French Agency for Food, Environmental, and Occupational Health and Safety. For this study, data were from adults above the age of 18 y, leading to a total sample of 2624 individuals in 5 subpopulations, distributed as 922 women < 50 y, 418 women between 50 and 64 y, 197 women ≥ 65 y, 936 men < 65 y, and 151 men ≥ 65 y.

    The average daily dietary intake, also called the observed diet was estimated based on 212 frequently consumed food items. After the removal of alcoholic items from food consumption, composition, and price databases, nutrient intakes and costs associated with the consumption of 207 food items were estimated for each subpopulation, leading to 5 observed diets.

    The authors then used mathematical optimization models developed based on the simplex algorithm. An optimization model is comprised of variables, constraints, and an objective function, and the algorithm finds the value that each variable must have to comply with the constraints while optimizing (i.e., minimizing or maximizing) the value given by the objective function. In diet optimization models, the variables are the quantities of foods, and the algorithm finds the quantity of each food in the modeled diet that is compatible with the simultaneous fulfillment of all constraints for the minimum (or maximum) value of the objective function.

    They used two kinds of models. Model set #1 diets were developed to determine the minimum protein contents compatible with the fulfillment of all nutrient recommendations (without imposing a minimum amount of total proteins), without changing the observed energy content, and without exceeding the observed diet cost. Model set #2 diets were aimed at determining the minimum percentages of animal proteins in total proteins compatible with the fulfillment of all nutrient-based recommendations without changing the observed energy content, without exceeding the diet cost, and taking eating habits into account.

    They used certain restraints for various important nutrition factors to meet the recommended dietary intake levels for certain age and sex groups.  Their model 1 showed that a strict minimum of at least 48 g/d of total proteins was needed to meet nutrient-based recommendations for nutrients other than proteins.

    Model 2 better at taking eating habits into account showed that the animal protein contributions to total proteins, which were approximately 70% in observed diets, could be reduced to contributions that were between 45% and 60%, specifically, animal protein contributions of 60% (men ≥ 65 y), 55% (women < 50 y and ≥ 65 y), 50% (women 50–64 y), and 45% (men < 50 y), depending on age and sex, while still being compatible with complete nutritional adequacy and affordability.

    Lower percentages would either be mathematically unattainable or constraints would have to be relaxed or removed, therefore impairing nutritional adequacy and/or realism in the resulting modeled diets. Numerous nutritional constraints were binding in model set #1, achieving the recommended levels was difficult for nutritional factors such as vitamin D, zinc, fiber, and alpha-linolenic acid in all subpopulations and iodine, calcium, and magnesium in some subpopulations. Regarding iron, the constraint was binding only for young women.

    Even though this study was mathematical modeling which was a theoretical simulation, the results may provide some insights: 1). 48 g/d of total proteins is about the minimum to meet nutrient-based recommendations for nutrients; 2). Some animal foods in the diet are needed since the lowest animal protein contributions to total proteins that are compatible with nutritional adequacy, affordability, and eating habits vary from 45% to 60%, depending on age and sex, with the highest contributions needed for older populations and young women.

    As the paper has also illustrated that achieving a nutrient adequate diet is not easy. Many nutritionists including myself have experienced the challenges in helping people to improve their dietary habits to not only include a variety of healthy foods but also meet the nutritional requirements. These study results tell us that moving towards diets with lower animal protein contributions or fully vegan diets would necessarily require nutritional supplementation to cover adult nutritional requirements.

Reference:

Florent Vieux, Didier Rémond, Jean-Louis Peyraud, Nicole Darmon. Approximately Half of Total Protein Intake by Adults Must be Animal-Based to Meet Nonprotein, Nutrient-Based Recommendations, With Variations Due to Age and Sex. The Journal of Nutrition, Volume 152, Issue 11, November 2022, Pages 2514–2525, https://doi.org/10.1093/jn/nxac150

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