An infant’s rate of weight gain during the first year of life can strongly predict obesity later in life.1 Various studies published in recent years have linked cow-milk protein with weight gain for infants.2, 3 Collectively, these studies have led to recommendations that protein should not exceed 15% of total energy during later-infancy and the second year of life.4 Such recommendations, however, don’t differentiate between dairy protein and protein from other sources. Could dairy protein be uniquely problematic, causing weight-gain problems not associated with meat protein? According to 2014 study published in the American Journal of Clinical Nutrition, yes.
Human breast milk contains progressively less protein during later-stages of lactation, particularly the 4-6 month window when infants start consuming complementary foods (while continuing to breastfeed). But how much protein should those complementary foods contain? Would a higher-protein diet be beneficial, provided the protein comes primarily from sources other than dairy? This was the hypothesis for the 2014 study mentioned above. Accordingly, the scientists tested complementary diets with both higher and lower amounts of protein, observing the effects on infants’ growth and their metabolic profiles.5
42 infants five or six months old were randomly assigned to one of two groups. For four months (six to nine months after birth), Group 1 (higher protein) ate complementary diets consisting of meat purees, whereas Group 2 (lower protein) ate iron- and zinc-fortified cereal purees. To qualify for the study, infants had to have had normal birth weights, be breastfed since birth, to continue being breastfed during the study, and no abnormalities nor conditions that would influence growth rate. For both groups, fruits, vegetables, yogurt, and cheese were also allowed (and continued breastfeeding was required). Energy intake for both groups was nearly identical, but with significant differences in macronutrient distributions. By the ninth month, the groups’ calorie consumption were:
The study yielded two major findings. First, despite widely differing macronutrient ratios, caloric consumption between the two groups was nearly identical. This suggests that infants can effectively regulate energy intake; they’re not prone to overeating because they know when to stop. The second finding was that diets higher in protein are associated with greater linear growth and proportional weight gain. This is a key point. Dairy protein intake during infancy has been correlated with obesity by age seven. In other words, increased weight gain absent proportional linear growth.
So why would milk protein promote obesity/overweight but meat protein promote proportional height/weight gains? The answer is not entirely clear, but the study’s scientists propose two mechanisms. First, dairy, but not meat, could promote the stimulation of insulin-like growth factor I (IGF-I), which in turn could promote obesity/overweight. Second, meat provides plenty of bioavailable zinc and iron, whereas neither dairy nor breast milk provide these nutrients in quantities sufficient to meet the nutritional needs of older infants (greater than six months).6
Although the scientists acknowledge their study requires follow-up research, their findings “reinforce the potential value of introducing flesh foods early.” Indeed, the available research supports the Paleo diet during all stages of life, including infancy. Compared to dairy- and cereal-based complementary diets, meat fares best for infants after six months of breastfeeding. Meat promotes increased growth and proportional height/weight.
Christopher James Clark, B.B.A. is an award-winning writer, consultant, and chef with specialized knowledge in nutritional science and healing cuisine. He has a Business Administration degree from the University of Michigan and formerly worked as a revenue management analyst for a Fortune 100 company. For the past decade-plus, he has been designing menus, recipes, and food concepts for restaurants and spas, coaching private clients, teaching cooking workshops worldwide, and managing the kitchen for a renowned Greek yoga resort. Clark is the author of the critically acclaimed, award-winning book, Nutritional Grail.
 Young BE, et al. (Sep 2012). Biological Determinants Linking Infant Weight Gain and Child Obesity: Current Knowledge and Future Directions. Advances in Nutrition, 3. Retrieved from //advances.nutrition.org/content/3/5/675.full
 Koletzko B, et al. (Jun 2009). Lower protein in infant formula is associated with lower weight up to age 2 y: a randomized clinical trial. American Journal of Clinical Nutrition, 89(6). Retrieved from //www.ncbi.nlm.nih.gov/pubmed/19386747
 Escribano J, et al. (Apr 2012). Effect of protein intake and weight gain velocity on body fat mass at 6 months of age: the EU Childhood Obesity Programme. International Journal of Obesity (London), 36(4). Retrieved from //www.ncbi.nlm.nih.gov/pubmed/22310472
 Michaelsen KF, et al. (Oct 2012). Amount and quality of dietary proteins during the first two years of life in relation to NCD risk in adulthood. Nutrition, Metabolism, and Cardiovascular Diseases, 22(10). Retrieved from //www.ncbi.nlm.nih.gov/pubmed/22770749
 Tang M and Krebs N. (Oct 2014). High protein intake from meat as complementary food increases growth but not adiposity in breastfed infants: a randomized trial. American Journal of Clinical Nutrition, 100. Retrieved from //ajcn.nutrition.org/content/early/2014/08/13/ajcn.114.088807
 Krebs NF, et al. (Jul 2012). Comparison of complementary feeding strategies to meet zinc requirements of older breastfed infants. American Journal of Clinical Nutrition, 1(30). Retrieved from //www.ncbi.nlm.nih.gov/pubmed/22648720