Background: Previous studies suggest that dietary protein might play a beneficial role in combating obesity and its related chronic diseases. Total, animal and plant protein intakes and their associations with anthropometry and serum biomarkers in European adolescents using one standardized methodology across European countries are not well documented.
Objectives: To evaluate total, animal and plant protein intakes in European adolescents stratified by gender and age, and to investigate their associations with cardio-metabolic indicators (anthropometry and biomarkers).
Methods: The current analysis included 1804 randomly selected adolescents participating in the HELENA study (conducted in 2006-2007) aged 12.5-17.5 y (47% males) who completed two non-consecutive computerized 24-h dietary recalls. Associations between animal and plant protein intakes, and anthropometry and serum biomarkers were examined with General linear Model multivariate analysis.
Results: Average total protein intake exceeded the recommendations of World Health Organization and European Food Safety Authority. Mean total protein intake was 96 g/d (59% derived from animal protein). Total, animal and plant protein intakes (g/d) were significantly lower in females than in males and total and plant protein intakes were lower in younger participants (12.5-14.9 y). Protein intake was significantly lower in underweight subjects and higher in obese ones; the direction of the relationship was reversed following after adjustments for body weight (g/(kg.d)). The inverse association of plant protein intakes was stronger with BMI z-score and body fat percentage (BF%) compared to animal protein intakes. Additionally, BMI and BF% were positively associated with energy percentage of animal protein.
Conclusions: This sample of European adolescents appeared to have adequate total protein intake. Our findings suggest that plant protein intakes may play a role in preventing obesity among European adolescents. Further longitudinal studies are needed to investigate the potential beneficial effects observed in this study in the prevention of obesity and related chronic diseases.
Alex’s Notes: From a practical standpoint, high-protein intakes (within reason of course) have been shown to be critical for maintenance of energy expenditure, preservation of lean body mass during dieting, and growth of lean body mass during overfeeding. Even in infants, increasing the consumption of meat as a complementary food to breast milk has been shown to improve growth and increase lean body mass without increasing adiposity. From a biological standpoint, animal-based proteins are of the greatest quality, containing all essential and nonessential amino acids is significant quantities. Conversely, plant-based proteins (with a few exceptions) are considered “incomplete” because they lack one of more essential amino acids.
However, plant foods also contain countless non-nutritive compounds (e.g. antioxidants; phytochemicals) that play a role in health. Plant foods also provide other nutrients of interest such as fiber. The current study was thus conducted to evaluate total, animal, and plant protein intakes in European adolescents and their associations with cardio-metabolic health.
The data for this analysis comes from the Healthy Lifestyle in Europe by Nutrition in Adolescence - Cross Sectional Study (HELENA-CSS), which was a European Commission funded project on lifestyle and nutrition among adolescents from ten cities within the European Union. Participants were between the ages of 12.5-17.5 years and dietary intake was collected through two non-consecutive 24-hour dietary recalls. Physical activity was assessed for seven days using an accelerometer.
Ignoring the intrinsic flaws of dietary recalls, what were the results?
A total of 1,804 boys and girls were included in the study analysis, 279 (15%) of whom were overweight or obese. Additionally, 57% were aged 12.5 to 15 years, with the remainder being 15 to 17.4 years old.
|Energy Intake (kcal/day)||Total protein (g/d)||Total protein (g/kg/d)||Animal protein (g/d)||Plant protein (g/d)||Plant protein (% of total energy)|
|Normal weight||2460||96 (15.7%)||1.8||58||38||6.2%|
Bring attention to the table above, the average protein intake was 15.8% of total energy intake with animal proteins making up the majority. This comes out to about 1.7g/kg of bodyweight for the cohort. More interesting, in my opinion, is the results stratified by weight status. For instance, underweight and obese kids were eating the same amount of calories and protein. In fact, the total protein intake per kg of bodyweight had a significant reduction as weight status increased.
When looking to body composition variables as assessed by skinfold measurements, there was a significant decline in body fat percentage (BF%) as protein intake increased, with no sex differences. However, after adjustments for dietary fat intake, country of origin, age, gender, and tanner stage were made, only plant-based protein maintained a significant inverse relationship with BF% when expressed as grams per day only and not as a percentage of energy intake. Since the only way to consume more plant protein per day is to eat more plants, this warrants extreme (in my opinion) skepticism for two reasons. First, plants have countless other compounds that are beneficial for health and body composition. Second, it does not make biological sense for plant proteins to be more beneficial than animal proteins given they are inferior protein sources.
On a similar note, after all adjustments for the potential confounding variables were made, only serum HDL-cholesterol was positively associated with absolute animal protein intake. No other serum biomarkers had significant relationships.
This study suggests that increasing protein intake in adolescents is associated with a reduced body fat percentage. That is definitely beneficial. Moreover, it appears that plant-based proteins are more beneficial in this regard. While I would be hesitant to stop eating animal-based foods, the idea that increasing plant intake reduces body fat is not new. Moreover, when we consider what plant foods are rich in protein, such as nuts and grains, it is not entirely surprising that they are associated with reduced body fat. Previous research has demonstrated that the most protective foods against weight gain are fruits, nuts & seeds, vegetables, and whole-grain cereals.