Daily branch chained amino acid intakes and the risk of obesity among women with prior gestational diabetes mellitus

Some studies have found that branched amino acid (BCAA) is associated with the risk of obesity among general population, however, not all the results were consistent. The present study aimed to investigate the association of daily BCAA intakes with the risk of postpartum overweight and abdominal obesity among women with prior gestational diabetes mellitus (GDM). We performed a cross-sectional study of 1263 women with prior GDM at 1–5 years post-delivery. Logistic regression models were used to estimate the association of daily dietary intakes of BCAAs with the risk of overweight and abdominal obesity. and for abdominal obesity, respectively. the quartile signicantly increased compared with women at quartile of daily BCAA intakes after further adjustment of daily energy intake.

The estimated global prevalence of GDM is 12.8% according to the 9th edition of International Diabetes Federation atlas (4). A recent meta-analysis has shown that the prevalence of GDM in mainland China is 14.8% (5). Women with GDM have a 7.43-fold higher risk of postpartum diabetes than women with normal blood glucose during pregnancy (6). Postpartum obesity is one of most important risk factors for postpartum diabetes among women with GDM (7). Our recent study indicated that the 1-year early postpartum lifestyle intervention led to signi cant weight loss in women with prior GDM, the effect of which was more pronounced in women who were overweight at baseline (8).
Over the past decades, more researchers have assessed the association of daily branch chain amino acid (BCAA) intakes with the risks of obesity and related metabolic disorders, however, the results were inconsistent. BCAAs include a group of essential amino acids, such as leucine, isoleucine and valine.
These three BCAAs account for one third of the dietary essential amino acids and make up for 20% of the total protein content (9). Several studies demonstrated that high BCAA levels were associated with increased risks of obesity, insulin resistance and type 2 diabetes in adults and children (10) (11) (12) (13).
Nevertheless, data from the "INTERMAP STUDY" showed that higher BCAA intake had a lower prevalence of overweight and obesity in middle aged East Asian and Western adults (14). Although women with prior GDM have high prevalence of postpartum overweight and obesity (15), no studies have assessed whether the postpartum daily BCAA intakes would in uence the risks of general overweight and abdominal obesity among women with prior GDM. In the present study, we examined associations between daily dietary intakes of BCAAs and the risks of postpartum general overweight and abdominal obesity among women with a history of GDM.

Study population
Tianjin GDM Prevention Program is an early postpartum lifestyle-intervention trial in Tianjin, China (16).
The detailed study design and methods were previously described (8,16

Questionnaires and measurements
At the baseline survey, all participants completed a self-administered questionnaire and underwent a physical examination. They also completed the 3-day 24-hour food records taught by a dietician. The self-administered questionnaire included socio-demographics (age, marital status, education, income, and occupation), family history of diabetes, pregnancy outcomes (pre-pregnancy weight, weight gain in pregnancy and number of children), postpartum weight, smoking habits (non-smoking, former smoking, current smoking), passive smoking status, alcohol intake, leisure time physical activity (0 minute/day, < 30 minutes/day, and ≥ 30 minutes/day). Dietary assessments were obtained from the 3-day 24-h food records, which were carried out on three continuous days (two weekdays and one weekend day). The food was weighted separately with a scale before being cooked or the portion sizes were estimated. After completion, the records were reviewed and coded by a dietitian. Food was divided into 18 groups and averages of the 3-day food energy and nutrient intakes including BCAAs (including leucine, isoleucine, The BMI cut-points in the Chinese population were 24 ≤ BMI < 28 kg/m 2 for overweight and BMI ≥ 28 kg/m 2 for obesity (20); abdominal obesity was de ned as waist circumference ≥ 80 cm for women (21).

Statistical analysis
Demographic and lifestyle data were revealed according to the quartiles of daily BCAA intakes. One-way ANOVA and chi-square tests were used to assess the differences in continuous and categorical variables according to the quartiles of daily intakes of BCAAs. Logistic regression was used to estimate the odds ratio (OR) and 95% con dence interval (CI) of general overweight and abdominal obesity by quartiles of daily BCAA intakes. The analyses were rst adjusted for age (Model 1); then for education, family income, family history of diabetes, current smoking, passive smoking, current alcohol drinking, leisure time physical activities, and sitting time (Model 2); and further for daily energy intake (Model 3). We used the restricted cubic spline nested in logistic regression to test whether there was a dose-response or nonlinear association of daily BCAA intake as a continuous variable with the risk of obesity. All the statistical analyses were performed with SPSS statistics V.25.0 for Windows software package (IBM) and SAS for Windows version 9.3 (SAS Institute Inc., Cary, NC, USA). Two-sided P < 0.05 was considered statistically signi cant.

Results
General characteristics of the study population according to quartiles of daily BCAA intakes are presented in Table 1. Current alcohol drinking, daily energy intake, energy intake from fat, energy intake from protein, and energy intake from carbohydrate were positively associated daily BCAA intakes.

Discussion
The present study found U-shaped associations of daily intakes of BCAAs, isoleucine, leucine, and valine with the risks of general overweight and abdominal obesity among women with a history of GDM. A signi cantly increased risk of obesity was observed among women with the lowest quartiles of daily BCAA intakes compared with women at quartile 2 of BCAA intakes.
The prevalence of obesity has increased rapidly in China (22). Many factors account for the rapid increase in obesity, including more sedentary behavior and a high energy/high fat diet (22). The present study indicated that daily lower and higher intakes of BCAAs were associated with higher risks of general overweight and abdominal obesity among women with prior GDM. BCAAs are a group of essential amino acids, which are not produced in body but can only be obtained from the diet (23). Several studies have assessed the association between daily consumptions of BCAAs and the risk of obesity, and results were full of controversy. The "INTERMAP STUDY" and one study in northern China supported the inverse association between daily BCAA intake and the risks of general overweight/obesity and abdominal obesity (14) (24). However, another Chinese study indicated positive associations of daily BCAA intake with mean values of BMI and waist circumference, as well as the risks of metabolic syndrome and cardiovascular disease (25). Several clinical trials have also evaluated the association between daily BCAA levels and the risk of obesity. A protein-restricted diet could help improve metabolic indexes, including obesity and insulin resistance (26). Another animal study pointed out that the restriction of dietary BCAAs signi cantly decreased body weight and adiposity, and increased energy expenditure (27). However, very few studies have assessed the effects of dietary BCAA restriction on metabolism in humans (28). Two trials have found that weight loss induced by either gastric bypass surgery or sleeve gastrectomy among severely obese patients causes the same decline in circulating BCAAs (29,30).
GDM is a serious pregnancy complication worldwide (31). Women with a history of GDM have a marked increase in type 2 diabetes risk later in life (32). It has been found that women exposed to GDM generally have a higher BMI after delivery, (15) and postpartum obesity is one of most important risk factors of postpartum diabetes (33). However, very few studies have assessed how BCAA intakes in uence the risks of overweight and central obesity among women with a history of GDM. The present study found that daily higher and lower intakes of BCAAs, isoleucine, leucine, and valine assessing by a 3-day 24-hour food record were associated with increased risks of general overweight and abdominal obesity among women with prior GDM.
The mechanisms of BCAAs and metabolic disorders are complicated. Studies in human and rodent adipose tissues have demonstrated a reduced expression and activity of mitochondrial branched-chain aminotransferase (BCATm) and branched-chain keto acid dehydrogenase (BCKDH) in an obese condition (34) (35). Another study has suggested that impaired adipokine signaling (leptin versus adiponectin) is a key element in the obesity-driven changes in circulating BCAA levels (36). Moreover, elevated BCAA levels are highly effective activators of the mTOR signaling pathway and persistent activation of mTORC1 promotes insulin resistance through serine phosphorylation of IRS-1 and IRS-2 (37) (38). Thus, the increased circulating BCAAs might have a connection with obesity. Although diet is the only source of BCAAs and 80% of the dietary BCAAs reach blood circulation (39), the relationship between BCAA intakes and obesity risk was not coincident with the BCAA concentrations. As many investigations indicated that BCAA supplementation had an inverse association with weight, the potential mechanisms were postulated as follows: rst, leucine directly into brain could activate the hypothalamic mTOR signaling and decrease food intake and body weight (40) (41). Second, leucine supplementation stimulated the increase of leptin, which can suppress dietary appetite and food intake resulting in decreasing body weight (42) (43). Third, the hydrolysis of dietary protein releases leucine in the gastrointestinal tract, which can stimulate the production of cholecystokinin and glucagon-like peptide 1 (anorexigenic hormones) and thus inhibit the production of ghrelin (orexigenic hormones) by activating the mammalian target of rapamycin (44). On the contrary, some other researchers insisted that restriction of BCAA intakes was a approach for weight loss through stimulating the induction of FGF-21 expression, which has shown the effect on weight loss (45).
There were some strengths in the present study. First, this is a large epidemiological study of GDM and this study enrolled a large amount of women with a history of GDM in Tianjin, China. Second, the quantity of BCAA intakes was measured by a 3-day 24-hour food record that is different from previous studies and more practical for adjustment of the daily diet structure. Third, as far as we know, many investigations focused on the association of dietary BCAA intakes with the risk of obesity in the general population. This is the rst study aiming at women with prior GDM in a short postpartum period. There were also some limitations in the present study. First, this study had a cross-sectional design that limited the reference as the causal association between daily BCAA intakes and the risk of obesity. Second, the present study only aimed at women with GDM in China. It could not represent the general population.
Therefore, future studies are needed to verify the situation in larger regions worldwide. Third, the measurement of BCAA intakes in our study was only in a short term, which may be less representative of individuals' long term dietary patterns.

Conclusion
Page 13/17 The present study indicated that the daily lowest quartile of BCAA intakes was signi cantly associated with great risks of general overweight and abdominal obesity among women with a history of GDM after a short time of delivery. Only moderate BCAA intakes were bene cial for weight control and avoiding abdominal obesity. In the future, more clinical trials are needed to verify this issue. Availability of data and materials: the datasets generated and analysed during the current study are not publicly available, but are available from the corresponding author on reasonable request.
Competing interests: the authors declared that they had no competing interests.
Funding: This study is supported by the grant from European Foundation for the Study of Diabetes