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Reduced-protein Nordic diet lowers infant plasma BCAAs and links protein intake to IGF-1 and weightDoes less protein in baby food help slow rapid weight gain?

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Key Takeaway
Consider that reduced-protein complementary feeding may lower infant BCAAs and influence growth via IGF-1 pathways, but evidence is associative.

This secondary analysis of a randomized controlled trial examined 250 infants followed for 18 months. Infants received either a reduced-protein Nordic complementary diet or a conventional Swedish complementary diet. The primary focus was on metabolic responses using plasma metabolomics and pathways linking cumulative protein intake to circulating biomarkers and growth outcomes.

Infants in the reduced-protein Nordic diet group had significantly lower plasma branched-chain amino acids (BCAAs) and catabolites compared to the conventional diet group, though exact effect sizes were not reported. Structural equation modeling revealed positive correlations between cumulative protein intake and plasma IGF-1 (β = 0.40-0.43), and between plasma total BCAAs and IGF-1 (β = 0.16-0.17). After accounting for metabolite-mediated effects on IGF-1 and insulin, cumulative protein intake remained significantly associated with infant body weight (β = 0.36, 95% CI: 0.02, 0.99) but not with BMI.

Safety and tolerability data were not reported. Key limitations include the secondary analysis design, which means findings should be interpreted as associations rather than causation. Some confidence intervals included zero or near-zero values, indicating uncertainty in effect estimates. The analysis does not establish clinical significance of effect sizes or long-term obesity outcomes beyond 18 months.

For practice, this mechanistic research suggests reducing protein intake during complementary feeding may help attenuate rapid infant weight gain through metabolic pathways involving BCAAs and IGF-1. However, clinicians should recognize these are exploratory findings from modeling analyses that require confirmation in primary trials with clinical endpoints.

Imagine choosing the first solid foods for your baby. You want them to grow strong, but you also worry about them becoming overweight later. This study looked at how different diets affect that early growth. Researchers compared a lower-protein Nordic diet against a conventional Swedish diet for 250 infants followed for 18 months. They used advanced blood tests to see how these foods changed the body's chemistry.

The findings showed that babies on the lower-protein diet had lower levels of certain amino acids and growth signals in their blood. More importantly, the data suggested that eating less protein helped slow down rapid weight gain. This is a big deal because fast weight gain in infancy is a known warning sign for obesity later in life.

But there are important caveats. This was a secondary analysis of an existing trial, meaning the main goal wasn't to prove this specific link. The math shows connections, not direct cause-and-effect. Also, the study only tracked babies for 18 months, so we do not yet know if these early changes lead to healthier kids years down the road.

What this means for you:
Lower-protein baby food may slow early weight gain, but long-term benefits are not yet proven.

Study Details

Study typeRct
EvidenceLevel 2
PublishedApr 2026
View Original Abstract ↓
BACKGROUND: Protein intake among children in resource-rich countries often exceeds current recommendations. Higher protein consumption during infancy has been associated with an increased risk of obesity later in life. OBJECTIVES: We conducted a secondary analysis of a randomized controlled trial where 250 infants were randomly assigned to receive either a protein-reduced Nordic diet or a conventional Swedish complementary diet. Our aims were to examine the metabolic responses to the intervention using plasma metabolomics and to test the pathways proposed by the Early Protein Hypothesis by linking cumulative protein intake to circulating branched-chain amino acids (BCAAs), insulin-like growth factor-1 (IGF-1), and growth outcomes using structural equation modeling (SEM). METHODS: Targeted proton nuclear magnetic resonance (H-NMR) metabolomics was performed on plasma samples collected at 12 and 18 mo. Two SEM models were constructed: one modeled body weight and the other modeled BMI as growth outcomes using data collected up to age 18 mo. Model fit indices were assessed, and path diagrams were used to visualize relationships. RESULTS: The Nordic diet led to reduced-protein intake and a distinct infant plasma metabolomic profile. Circulating BCAAs and their catabolites were significantly lower in the reduced-protein Nordic diet compared with the conventional diet. Cumulative protein intake positively correlated with plasma IGF-1 concentrations {weight-based SEM: β = 0.40 [95% confidence interval (CI): 0.03, 0.48]; BMI-based SEM: β = 0.43 [95% CI: 0.05, 0.50]}. Plasma total BCAAs were positively associated with plasma IGF-1 levels [weight-based SEM: β = 0.16 (95% CI: 0.00, 0.76); BMI-based SEM: β = 0.17 (95% CI: 0.02, 0.78)]. After accounting for metabolite-mediated effects on IGF-1 and insulin, cumulative protein intake remained significantly associated with infant body weight [β=0.36 (95% CI: 0.02, 0.99)], but not BMI. CONCLUSIONS: Complementary feeding during infancy substantially shapes the plasma metabolome. Reducing protein intake from complementary feeding helps attenuate rapid infant weight gain, a well-established early-life predictor of later obesity.
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