Obesity during childhood has become a major public health challenge in the United States.^1–3 Childhood obesity increases the risk of several health conditions, including high blood pressure, dyslipidemia, and insulin resistance.^4–6 In addition, childhood obesity increases the likelihood of entering adulthood with obesity,⁷ which in turn contributes significantly to the development of chronic diseases, such as type 2 diabetes, cardiovascular disease, and certain types of cancer.^8–10 Effective strategies for preventing childhood obesity are critically needed to halt the rising rates of chronic health conditions in adulthood.

A growing body of evidence suggests that maternal lifestyle before or during pregnancy contributes to the risk of obesity in offspring.^11–19 Among modifiable lifestyle factors, maternal obesity and smoking are known to have adverse effects on pregnancy outcomes^{20, 21} and long-term consequences among offspring through increasing the risk of obesity during childhood.^11–14 In addition, studies focusing on offspring obesity have also suggested that unhealthy dietary pattern and physical inactivity during pregnancy are associated with an increased BMI in offspring.^15–19 However, no studies have determined the effects of adopting an overall healthy lifestyle before pregnancy that consists of multiple healthy lifestyle and dietary practices, such as having a healthy body weight, no smoking, regular physical activity, and consumption of a healthful diet, that could jointly produce greater health benefits than any individual factors.²² In women, adhering to such an overall healthy lifestyle was associated with a dramatically reduced risk of developing cardio-metabolic conditions.^23–25 Whether such a healthy lifestyle exerts any intergenerational effects on child health deserves examination.

Evaluation of an overall lifestyle before pregnancy in relation to offspring obesity risk is biologically meaningful. Accumulating evidence shows that lifestyle factors (e.g., smoking) have long-lasting effects on DNA methylation, which in turn might lead to changes in gene expression and ultimately to the development of diseases later in life.^{26, 27} Since epigenetic modifications remain relatively intact even after the interruption of environmental exposures (i.e., smoking cessation)²⁶ and epigenetic traits can be passed from mothers to their offspring,²⁸ a process named intergenerational epigenetic inheritance,²⁹ it is likely that mothers’ lifestyle before pregnancy may have lasting effects on children’s health. Of note, a survey showed that women were willing to change their behaviors to adopt a healthier lifestyle during pregnancy,³⁰ although an overall long-term pre-pregnancy lifestyle may also play a critical role in children’s health.

To address this novel research question, we prospectively examined the association of an overall maternal lifestyle before pregnancy with risk of obesity in their children using data from mother-child pairs enrolled in the Nurses’ Health Study II (NHSII) and Growing Up Today Study 2 (GUTS2), respectively.

Baseline characteristics of the 5,701 offspring and their 4,698 mothers are presented in Table 1. Women were on average 33 years old at the delivery, had a healthy body weight (mean BMI 23.0), and did not smoke (92.6%) before pregnancy. The offspring population included more girls (53.1%) than boys.

We identified 520 (9.1%) offspring who were ever obese during follow-up. Table 2 shows the associations between individual maternal lifestyle factors and risk of offspring obesity during childhood through early adulthood. In multivariable analysis, offspring born to women with obesity (BMI≥30) had an RR of 4.15 (95% Cl: 3.36-5.13) of developing obesity, compared to children born to mothers with a BMI of 18.5-25. Offspring of women who smoked before pregnancy were also at a higher risk (RR 1.64, 95%CI 1.25-2.15) of having obesity than children of mothers who never smoked. Pre-pregnancy AHEI diet score and moderate-vigorous physical activity were not associated with the risk of offspring obesity.

Table 3 presents the association between low-risk lifestyle factors in women and risk of obesity in offspring. The risk of offspring obesity was 63% (RR 0.37, 95%CI 0.31-0.43) lower in children of women with a healthy weight compared to the rest. Compared to offspring of women who smoked before pregnancy, children of non-smoking mothers had 36% (RR 0.64, 95%CI 0.49-0.84) lower risk of obesity. Adherence to a healthy diet and regular physical activity were not significantly associated with offspring obesity risk; the RRs (95% CIs) were 0.98 (0.82, 1.17) and 0.90 (0.76, 1.08), respectively.

When we grouped women based on the number of low-risk factors, a higher number of low-risk factors was significantly associated with a lower risk of offspring obesity (Figure 1 and Supplementary Table 1). Offspring born to women who adhered to all four low-risk factors had 75% lower risk (RR 0.25, 95%CI 0.14-0.43) of obesity, compared to children born to mothers who did not adhere to any low-risk factor. The corresponding PAR was 55.1% (95%CI 41.9%-63.2%). These associations did not change materially when analyses were stratified by gender (Supplementary Figure 3 and Supplementary Table 2) and were strengthened when we evaluated the low-risk factors in relation to persistent obesity in offspring (Supplementary Table 3). The risk of persistent obesity in offspring of mothers who adhered to 4 low-risk factors was 84% (RR 0.16, 95%CI 0.04-0.59) lower than in offspring of women who did not adhere to any low-risk factor. Adherence to three low-risk factors (healthy diet, >150 minutes/week of moderate/vigorous exercise, and non-smoking) was marginally associated with offspring obesity risk (RR 0.64, 95%CI 0.41-1.00), in comparison with offspring of women with no low-risk factors. Adjusting for BMI led to attenuated risk reduction of 12% (RR 0.76, 95%CI 0.49-1.16) and the mediation analysis showed that 47.9% of this association was explained by BMI (Supplementary Table 4).

We did not observe effect modification by established childhood obesity risk factors (all p>0.05 for interaction) (Table 4). Compared with offspring born to women who did not adhere to any low-risk factor, the effect estimates of obesity risk in offspring of women who adhered to all low-risk factors did not materially change by strata of gestational age, pregnancy complications, and pre-pregnancy BMI.

The time-varying analysis showed that compared to children born from women with any low-risk factor, offspring of women with four low-risk factors had 80% (RR 0.20, 95%CI 0.09-0.42) lower risk of obesity (Supplementary Table 5).

In this prospective investigation among US women and their children, we observed that a pre-defined overall healthy lifestyle before pregnancy characterized by maintenance of a healthy body weight, avoidance of cigarette smoking, moderate/vigorous exercise, and consumption of a healthful diet, was strongly associated with a lower risk of obesity in offspring. Offspring born to women who adhered to all four healthy lifestyle factors had 75% lower risk of developing obesity in childhood through early adulthood, in comparison with children born to mothers without any low-risk factors. We found that maternal lifestyle factors could explain 55% of offspring obesity during childhood through early adulthood. The majority of this relationship was explained by maternal pre-pregnancy BMI alone. These findings demonstrate the potentially important role of maternal lifestyle, especially weight control, before entering pregnancy in the development of obesity in offspring.

Several studies have been conducted to evaluate the role of lifestyle factors during pregnancy or the period proximal to pregnancy on the risk of offspring obesity. A meta-analysis evaluating the association of pre-pregnancy BMI with offspring obesity showed that children born to mothers who were obese had three times higher risk of obesity during childhood.¹¹ Findings from another meta-analysis including 236,687 children revealed that offspring of mothers who smoked during pregnancy had 55% greater risk of becoming obese during childhood than children of mothers who did not smoke.¹³ In contrast, the evidence is limited regarding the role of maternal physical activity and dietary patterns in relation to offspring obesity, and such evidence is primarily generated from investigations that focused on these lifestyle practices during pregnancy.^15–19 In 5,125 Greek mother-offspring pairs, higher physical activity levels during pregnancy were associated with a lower risk of offspring obesity at age 8 years.¹⁹ Regarding maternal diet, findings from a Danish study showed that maternal “western diet” consisted of high intakes of red and processed meat and high-fat dairy products was associated with higher risk of lower birth weight, which is a risk factor of childhood obesity.⁴⁴ In a US study, a higher AHEI score of maternal diet during pregnancy was not significantly associated with birth weight.⁴⁵ Lastly, a prospective study of Dutch mother-offspring pairs failed to demonstrate significant associations between either a healthy diet pattern or an unhealthy diet pattern consumed during pregnancy and body composition in children at age six after adjustment for other childhood obesity risk factors.¹⁵ Apparently, more evidence is needed to elucidate whether long-term physical activity levels and healthy diet practiced before pregnancy is beneficial for children’s metabolic health.

The data collected in the NHSII and GUTS2 allowed us to evaluate the joint effects of major lifestyle factors in women before pregnancy in relation to the risk of offspring obesity. We confirmed the findings of previous studies that maternal obesity is one of the most influential risk factors for obesity in offspring. Likewise, in line with previous reports, we found that pre-pregnancy smoking was independently associated with the risk of offspring obesity. The lack of significant association for physical activity and diet are unexpected, although lack of long-term repeated assessments of these factors before pregnancy may play a role in these null associations. Moreover, the adjustment of maternal BMI may account for partially the beneficial effects of eating a healthy diet and being physically active because maternal body weight control may likely operate in the causal pathways linking diet and physical activities with offspring health. Nonetheless, our results further suggest that the benefits of adhering to an overall healthy lifestyle exceed those of any single lifestyle factors.

A healthy lifestyle and diet may share many health effects in common which in combination contribute to a dramatic decrease in the risk of chronic diseases.^23–25 A consumption of healthy diet, maintaining a healthy body weight, regular physical activity, and avoidance of smoking could induce favorable metabolic and molecular alterations, resulting in improved insulin sensitivity, reduced systemic inflammation, and alleviated oxidative stress which in turn will delay the organ damage and consequently decrease the risk of chronic diseases.^{46, 47} In women, lifestyle factors could influence the development and programming of fetus through their effects on the intrauterine environment.¹⁴ When the intrauterine environment is exposed to metabolic stresses induced by hyperinsulinemia, inflammation, and other metabolic changes, the developmental programming and metabolic adaptation of fetus may be altered through epigenetic changes or the disturbance of the homeostatic control mechanisms, leading to an elevated risk of childhood obesity.⁴⁸ Indeed, findings from an offspring epigenome-wide human study identified 28 CpG sites that are differentially methylated in the offspring of mothers with obesity.⁴⁹ Other potential mechanisms could be ascribed to the development and function of adipose tissue, pancreas, liver, and brain of the fetus. Studies conducted in rodents showed that maternal obesity could promote morphology alteration of adipocytes in the fetus that is related to the development of offspring obesity.⁵⁰ Similarly, a maternal diet rich in calories during pregnancy is associated with adverse programming of the hypothalamus in the fetus which may lead to hyperphagia and obesity.⁵¹ Furthermore, research has shown that epigenetic modifications following environmental exposures could persist for several years even after the exposures stopped.²⁶ For example, an epigenome-wide study of cigarette smoking showed that methylation levels of 36 CpGs (among 2568 CpGs that were differentially methylated in a meta-analysis²⁶ comparing former versus never smokers) annotated to 19 genes (e.g., TIAM2, PRRT1, AHRR) in former smokers did not recover to never-smoker levels even after 30 years of smoking cessation.²⁶ In a review of the dynamics of epigenetic phenomena across generations, Burggren²⁸ has hypothesized that epigenetic traits could be transmitted from one generation to the next. These mechanisms may pertain to our novel findings that linked pre-pregnancy lifestyle with childhood obesity.

Strengths of our study include a large sample size, prospective study design with long follow-up, detailed pre-pregnancy information acquired by using validated questionnaires, and information on pregnancy which allowed us to conduct comprehensive analyses. Although our goal is to examine long-term lifestyle and dietary practices of mothers before they enter pregnancy in relation to their offspring’s health, we mainly used single assessment of lifestyle practices in this analysis to maintain a prospective temporality of the associations of interest. This may introduce misclassification of long-term lifestyle behaviors, although the impact of such a misclassification is likely to nullify the associations because of the prospective study design. Given the prospective study design, the possibility of recall bias is unlikely. Another limitation of our study is the lack of genetic information of mothers and offspring. The potential interactions between genetic predisposition and lifestyle or diet may also play a critical role in the development of obesity later in life.^{48, 52} NHSII participants are predominantly white, reflecting the race/ethnic composition of the nursing profession at the time of study enrollment. Therefore our results may not apply to other race/ethnic groups. In addition, the prevalence of specific chronic disease risk factors, such as obesity, is lower in our population compared to the general US population. More studies are warranted to extend this research to more general populations. Another limitation is that we used self-reported weight and height to estimate the obesity status among children, thus introducing measurement errors in outcome ascertainments. Nevertheless, it is unlikely that misclassification of obesity status was associated with maternal lifestyle before pregnancy, and therefore the measurement errors may likely attenuate true associations. In the current analysis, we focused on pre-pregnancy lifestyle practices and did not explicitly assess lifestyle during pregnancy and therefore could not separate the roles of lifestyle before and during pregnancy in the risk of childhood obesity. This remains a question for future studies. Lastly, as in any observational studies, we cannot exclude the possibility of uncontrolled confounding such as offspring physical activity and diet quality, or residual confounding.

In conclusion, we found that children of mothers who adhered to an overall healthful lifestyle before pregnancy had a substantially lower risk of obesity during childhood through early adulthood. Moreover, we observed a monotonic dose-response relationship of this association in that healthier lifestyle practices predicted greater reduction in childhood obesity risk, although clearly, maintaining a healthy body weight and non-smoking of the mom were the two single most critical maternal factors to predict offspring BMI. These findings underscore the importance of adopting an overall healthy lifestyle, particularly in women who plan a pregnancy, to prevent obesity and metabolic consequences later in life of their children.