a. Background
The 1st year of life is very important for later-in-life obesity and heart disease development. Studies have shown that protein intake from dairy is associated with rapid weight gain, which may increase later-in-life obesity risk. However, no studies looked at if this relation between protein and weight gain is true for all protein sources. For example, whether meat protein would also increase weight gain as dairy protein does in infants, is unknown. Moreover, bacteria found in the gut, are recently discovered to play an important role in weight regulation. Limited evidence suggest that meat vs. dairy has different impact on gut bacteria composition. Thus, we would like to address the problem of weight gain during infancy and its association between protein source and gut bacteria.
b. Objective(s)
1. Would different protein sources from meat and dairy result in different weight/fat gain in formula fed infants?
2. Would different protein sources from meat and dairy result in different bacteria profiles in the gut?

c. Methods
Five-month old, health, formula-fed infants were recruited from the metro Denver area. These infants were divided into two groups. One group consumed a meat-based diet and the other group consumed a dairy based diet, from 6 to 12 months of age. During this 7 months of consuming the study diet, blood, urine, and stool samples were collected at multiple time points for analyses of growth biomarkers, glucose metabolism, inflammation, body composition and the gut microbiota. Infant growth (e.g. length, weight, circumferences, skinfolds) were measured every month from 6 to 12 months of age. The same cow milk based infant formula was provided to all participants.
d. Important Findings
1) Infant weight and weight-for-age-Z scores increased over time. Both meat and dairy groups have the same amount of increase.
2) Infant length increased. However, length-for-age Z score, a parameter of linear growth status, increased in the meat group and decreased in the dairy group.
Weight-for-length Z score, a parameter of overweight risk, increased in the dairy group.
3) Meat consumption appears to be associated with a gut microbiome profile favoring beneficial strains.
e. Implications/Industry Impact
Currently, there is no emphasis on introducing meat as an important source of protein and micronutrients for older infants. WHO is very explicit for complementary feeding, noting: “Meat, poultry, fish or eggs should be eaten daily, or as often as possible” for older infants. However, survey data on infant feeding patterns in the U.S. confirm the pattern of late introduction of protein foods in general, and meats in particular. The data indicate that < 10% of 7-8 mo olds eat baby food or non-baby food meats. Current baby food market in the U.S. is $6 billion. Animal flesh protein such as pork, which is an excellent source of high quality protein and micronutrients, has not been promoted, whereas parents are more likely to offer yogurt and cheese as protein sources. Addition of more cow milk protein as complementary foods to a cow milk protein based formula diet may have adverse metabolic effects. The proposed research provides a novel approach via controlled feeding that directly compare meat vs. dairy on growth, body composition, blood biomarkers and gut microbiota changes in formula fed infants starting complementary feeding. Preliminary findings from this study suggest the meat and dairy protein have different effects on growth in formula fed infants, with meat having a potentially stronger linear growth promoting effect and a healthy gut microbiome. These data extend findings from studies in breastfed infants that meat is well tolerated as a complementary food, and may have metabolic and anthropometric advantages.