This study investigated the potential protective effects of short-term breastfeeding (lasting no more than 6 months) against childhood obesity. Our analyses revealed that, within the overall population in the present study, short-term breastfeeding did not demonstrate a significant direct association with a reduced risk of childhood obesity. However, the study identified that short-term breastfeeding exhibited some protective benefits in specific subpopulations, particularly among children born to mothers 35 years or older at the time of delivery. Furthermore, the study revealed that short-term breastfeeding experience interacted with the timing of formula and milk introduction, potentially modifying the associations between these early nutrition practices and childhood obesity risk.

Breastfeeding is recognized as one of the most effective strategies for ensuring child survival and overall health. It has been hypothesized to protect against childhood obesity through several potential mechanisms. Firstly, breastfeeding may promote the development of a healthy gut microbiota profile, which has been linked to a lower risk of obesity [25]. Secondly, it is highly conceivable that breastfeeding may mitigate the genetic influence on obesity development, potentially through DNA methylation mechanisms [11, 26]. Thirdly, breastfeeding is often associated with the adoption of healthier dietary patterns in children, which plays a crucial role in obesity prevention [27, 28]. While some previous epidemiological studies conducted in the past few decades raised concerns that observed associations between breastfeeding and reduced obesity risk might be due to residual confounding factors rather than a direct causal effect [23, 29], a growing body of recent research reaffirms the potential benefits of breastfeeding against obesity. A recent meta-analysis of 159 studies concluded that breastfeeding indeed reduces the odds of childhood obesity and that this effect is unlikely to be attributable to publication bias or residual confounding [9].

Previous studies investigating the protective effects of breastfeeding against childhood obesity often relied on comparisons between individuals with no breastfeeding experience or minimal breastfeeding duration (less than 6 months) and those breastfed for longer periods (e.g., exceeding 6 or even 12 months). Several studies suggest that certain benefits may only become evident when exclusive breastfeeding is sustained for more than 6 months [2, 8,9,10, 30,31,32]. However, despite WHO recommendations for exclusive breastfeeding for the first 6 months followed by continued breastfeeding for at least the first 2 years of life [33], this study using NHANES data found a substantial proportion (37.39%) of children discontinued breastfeeding within the first 6 months. This early termination rate aligns with findings from prior research [8, 10, 15,16,17]. Furthermore, an even higher proportion of participants in our study did not achieve exclusive breastfeeding for more than 6 months. In this context, the analyses of both the childhood obesity distribution and adjusted regression models did not detect a direct protective effect of breastfeeding against childhood obesity for these children.

While the present study did not observe a significant direct association between short-term breastfeeding (less than 6 months) and a reduced risk of childhood obesity in the overall population, it is important to consider the limitations of this categorical analysis approach. Several studies suggest a dose-dependent protective effect of breastfeeding duration, with some benefits potentially arising even from limited breastfeeding periods. For example, Li et al. [3] reported a decreasing trend in childhood obesity prevalence across groups transitioning from exclusive formula feeding to mixed feeding and then to exclusive breastfeeding, regardless of the specific proportion of breast milk in mixed feeding. This suggests a possible continuous, dose-dependent effect of breastfeeding on obesity risk. Similarly, Qiao et al. [2] employed a dose-response meta-analysis model and found that each additional month of breastfeeding was associated with an average 4% reduction in childhood obesity risk. While our subgroup analysis of the short-term breastfeeding group did not confirm a statistically significant effect using a categorical approach, these findings suggest that the potential benefit of short-term breastfeeding might be present but statistically masked or difficult to detect in our study. This possibility is further supported by the observation that the later introduction of the formula was associated with a lower risk of childhood obesity within the ever-breastfed subgroup, since later formula introduction suggests longer exclusive breastfeeding duration during early infancy. After all, breast milk and formula are the primary sources of nutrition in early life [34]. Our study also hints at potential effect modification by maternal age and household reference person gender. Furthermore, the observed trends in obesity incidence across age groups suggest that breastfeeding may be associated with a delayed onset of childhood obesity. Specifically, short-term breastfeeding duration was significantly associated with a lower obesity incidence in the 3-4-year-old age group, which aligns with findings from previous research [3]. These observations warrant further investigation using more comprehensive analytic approaches to explore potential dose-dependent effect and modification effects of short-term breastfeeding on childhood obesity risk.

The introduction of cow’s milk (regular milk) before 1 year of age is generally discouraged by some scientific society (e.g., American Academy of Pediatrics) due to its improper nutrient composition for infancy growth [35]. Soczynska et al. [36] reported no significant association between the timing of cow’s milk introduction and adiposity in children aged 3–5 years, which aligns with the preliminary findings of this study. However, our further analyses were conducted within subgroups defined by breastfeeding status (ever vs. never breastfed) among participants who had ever breastfed for ≤ 6 months. Interestingly, the earlier introduction of milk was associated with an adverse effect on children who were never breastfed, as evidenced by an increased risk of childhood obesity. This effect was not observed among children with any history of breastfeeding. These findings suggest that even a short duration of breastfeeding experience (≤ 6 months) may potentially mitigate the negative consequences of early milk introduction on childhood obesity risk. One possible explanation for this interaction is that the early introduction of cow’s milk might indeed promote a tendency towards childhood obesity. However, the experience of being breastfed, even for a short period, could potentially counteract this negative influence through various mechanisms, as discussed previously. These mechanisms may involve modifications to the gut microbiota profile, epigenetic regulation of gene expression, and the development of healthier eating behaviors. This study underscores the potential protective role of breastfeeding, even for relatively short durations, in the context of early milk introduction and its potential impact on childhood obesity risk.

This study offers several strengths and advantages. To our knowledge, it provides hitherto undocumented evidence of the potential benefits of short-term breastfeeding (lasting no more than 6 months) in protecting against childhood obesity within specific population subgroup. The findings provide valuable insights into the feeding patterns of children who breastfeed for ≤ 6 months. Additionally, the study leverages data from the NHANES, which offers a nationally representative sample, thus enhancing the generalizability of the results to the broader population. However, it is important to acknowledge certain limitations inherent to the study design. Firstly, the cross-sectional nature of NHANES data restricts our ability to establish a causal relationship between short-term breastfeeding (≤ 6 months) and a reduced risk of childhood obesity. Secondly, while the analyses adjusted for potential confounding variables, the possibility of residual confounding cannot be entirely eliminated. For example, factors such as maternal body mass index and gestational age at birth, which might influence childhood obesity risk, were not available in the dataset and could introduce unaccounted-for confounding effects. Lastly, the study is susceptible to recall bias, as data on early childhood nutrition were collected through questionnaires that rely on participants’ memory of events, potentially years in the past. To address these limitations and provide more robust evidence, future research efforts could benefit from large, prospective studies employing a longitudinal design. This approach would enable the collection of data over time and the establishment of stronger causal inferences.