We aimed to describe and characterize the gut microbiota composition and diversity in children with obesity according to their metabolic health status. Anthropometry, Triglycerides, HDL cholesterol, HOMA-IR, and systolic and diastolic blood pressure (SBP, DBP) were evaluated (and z-score calculated) and faecal samples were collected from 191 children with obesity aged from 8 to 14. All children were classified depending on their cardiometabolic status in either a "metabolically healthy" (MHO; n = 106) or "metabolically unhealthy" (MUO; n = 85) group. Differences in gut microbiota taxonomies and diversity between groups (MUO vs MHO) were analysed. Alpha diversity index was calculated as Chao1 and Simpson's index, and β-diversity was calculated as Adonis Bray-Curtis index. Spearman's correlations and logistic regressions were performed to study the association between cardiometabolic health and the microbiota. Children in the MUO presented significantly lower alpha diversity and richness than those in the MHO group (Chao1 index p = 0.021, Simpson's index p = 0.045, respectively), whereas microbiota β-diversity did not differ by the cardiometabolic health status (Adonis Bray-Curtis, R² = 0.006; p = 0.155). The MUO group was characterized by lower relative abundances of the genera Christensenellaceae R7 group (MHO:1.42% [0.21-2.94]; MUO:0.47% [0.02-1.60], p < 0.004), and Akkermansia (MHO:0.26% [0.01-2.19]; MUO:0.01% [0.00-0.36], p < 0.001) and higher relative abundances of Bacteroides (MHO:10.6% [4.64-18.5]; MUO:17.0% [7.18-27.4], p = 0.012) genus. After the adjustment by sex, age, and BMI, higher Akkermansia (OR: 0.86, CI: 0.75-0.97; p = 0.033), Christensenellaceae R7 group (OR: 0.86, 95% CI: 075-0.98; p = 0.031) and Chao1 index (OR: 0.86, CI: 0.96-1.00; p = 0.023) represented a lower risk of the presence of one or more altered cardiovascular risk factors. Lower proportions of Christensenellaceae and Akkermansia and lower diversity and richness seem to be indicators of a metabolic unhealthy status in children with obesity.

This article reviews the role of protein intake on metabolic programming early in life. The observations that breastfeeding in infancy reduces the risk of being overweight and obese later in life and the differences in the protein content between formula milk and human milk have generated the early protein hypothesis. The present review focuses on a mechanistic approach to programmed adiposity and the growth and development of other organs by protein intake in infancy, which may be mediated by branched-chain amino acids, insulin, and insulin-like growth factor 1 via the mammalian target of rapamycin. Observational studies and clinical trials have shown that lowering the protein content in infant and follow-on formulas may reduce the risk of becoming obese later in life. The recent body of evidence is currently being translated into new policies. Therefore, the evolution of European regulatory laws and recommendations by expert panels on the protein content of infant and follow-on formulas are also reviewed. Research gaps, such as the critical window for programming adiposity by protein intake, testing formulas with modified amino acids, and the long-term consequences of differences in protein intake on organ functionality among well-nourished infants, have been identified.