IFM Position on the Effect of Breastfeeding on Obesity

Background

Childhood overweight and obesity have reached epidemic proportions and are cause for global concern. Population studies have shown that breastfed infants tend to weigh less and it has been proposed that breastfeeding may provide protection against obesity into childhood and perhaps longer. Several theories have been advanced to explain how this may occur. Breastfeeding is a complex behaviour, however, often inversely associated with the same risk factors as being overweight [1]. Thus it is also possible that breastfeeding may be a proxy for overall lifestyles that counteract obesity in families [2].

The infant food industry has reviewed the body of scientific literature that examines the existing studies about the protective effects of breastfeeding. It offers the following observations on the scientific studies as well as other factors known to contribute to childhood obesity. 

Types of Studies Carried Out 

The best method to determine cause and effect of any factor is by use of randomised, prospective, controlled trials. However, any trial that would randomise breastfeeding would be unethical and thus cannot be conducted. Prospective studies are the next best solution and provide data which is more accurate than retrospective studies. However, because they are relatively more difficult to conduct, there are fewer of them, the number of subjects studied is significantly smaller, fewer associated factors are measured and they have less statistical power than larger, retrospective studies.

Therefore, most available studies on the effect of breastfeeding on obesity are retrospective, where the individuals' exposure to breast milk is commonly determined by archived reports, or, by for example, giving a questionnaire to the mothers some time, even many years, after birth. Such information has value, but carries with it the inbuilt bias that it is not always accurate.

Study Results

The findings of the many studies carried out over the last two decades are not consistent. Some studies show a small protective effect of breastfeeding against childhood obesity, some show no effect at all, and there are even studies showing that breastfeeding is positively linked with overweight or obesity.

• Studies showing an effect of breast-feeding against overweight and/or obesity also show that the effect is reduced when other factors such as maternal obesity or socio-economic status are considered. Many studies factored out some of the possible confounding factors, but none factored out all of them. Finally, some of the studies showed protective effects of breastfeeding against overweight and/or obesity in ways that are not biologically plausible. For example, Wadsworth et al showed the greatest risk of overweight or obesity occurred both in groups of children who were breast fed for the longest periods and in those never breastfed at all [2].
  
  
• Studies showing no effect frequently initially discovered significant protective effects although these disappeared completely when the data were corrected for the confounding factors, such as socio-economic status, parental obesity, mothers' smoking, birth weight, sex, gestational age, rates of early growth, sleep time, ethnicity, time of complementary feeding introduction, parental education, number of siblings, ethnicity, or television viewing [3, 4-11]. Although all these confounding factors have been found to influence the outcomes, generally not all of them are considered or were not all measured in any one study.
  
  
• A Meta Analysis by Owen [12] 2005 recently evaluated 36 studies which reported mean BMIs as a function of breast-feeding versus bottle-feeding. Initial results showed a small effect of lower BMI in infants who had been breastfed in infancy, but when this was adjusted for maternal BMI, half of the effect was abolished.  Where possible, studies were further adjusted for the additional factors of maternal socioeconomic status and maternal smoking which completely abolished the effect. Owen concluded that the differences in BMI in breastfed versus bottle fed subjects are small and likely to be strongly influenced by publication bias and confounding factors.

The hypothesis that breastfeeding protects against obesity is also not consistent with the fact that the incidence of breastfeeding has grown over the past decades in most countries of the world along with the growing epidemic of obesity [13, 14]. 

Other Factors Contributing to Childhood Obesity

Obesity is closely linked with lifestyle and environment. Contributions to the condition are many and varied - nutritional, social, cultural, economic, physiological, and genetic -- but dietary energy and/or insufficient energy utilisation are considered by experts to be its cornerstones. 

• Family influences - Parental overweight carries genetic and behavioural factors which create obesogenic versus non-obesogenic family environments that can have long-term effects, Davison et al [15].
  
  
• Socio economic class - Lower SES groups consume diets of lower quality, with less fruits and vegetables compared with those in higher SES [16].  
  
  
• Children's diets – Generally, they do not follow nutrition recommendations: rather they reflect children's liking for high fat, sugar, and salty foodstuffs [17].
  
  
• Physical activity - Studies show that the level of physical activity of children and adolescents has declined in most European countries [18] over the past few decades, as well as in the U.S. [19]. 

Conclusions

• Breastfeeding is the optimal feeding choice for infants and for many reasons it should be encouraged and supported wherever and whenever possible. But whether it protects against obesity is far from certain at this point in time. 
  
  
• If there is an effect, it appears to be small and frequently lost amidst very many more powerful lifestyle factors [8]. Mothers who breastfeed should definitely also take further measures to prevent their child's obesity as he or she grows up [4], [12].
  
  
• Any effect of breastfeeding on later obesity, if any, is probably weaker than genetic and other environmental factors [20], [21, 22] [23]. Obesity is more likely the result of a long-term imbalance in the food/activity mix and intensely subtle alterations in this equilibrium over long periods, rather than any short-term early influence. 
  
  
• Lack of clear-cut conclusions resulting from scientific studies are likely due to the fact breastfeeding is a complex behaviour with many confounding factors inextricably associated with the breastfeeding mother not often found with the mother who does not breast feed [24].
  
  
• In order to determine the influence of such confounding factors, they must be measured adequately and factored out of any analysis. Whether all the confounders are well measured, measurable, or even if they are known is unlikely, and this should be kept in mind when evaluating available studies.
  
  
• When confounding factors are accounted for correctly, apparent links between formula feeding and obesity always diminish and frequently disappear. Infant formula is the safest and most nutritious alternative to breast milk. It must contain all the micro and macro nutrients need to meet the nutritional needs of infants 0 to 6 months.
  
  
• The composition of infant formula is based upon scientific opinion from paediatric experts, such as ESPGHAN and it is strictly regulated by law. Infant formula manufacturers must comply with stringent national legislation when formulating and marketing their products.
  
  
• IFM welcomes scientific progress. Should scientific evidence show a clear link between formula and obesity, manufacturers will modify their products in accordance with any recommendations by scientific and government authorities.

References

1. Quigley, MA, Re: Duration of Breastfeeding and risk of overweight: a metanalysis. 2006: Am. J. Epidemiol. p. 870-875.
2. Wadsworth, J, S Marshall, R Hardy, and A Paul, Breastfeeding and obesity: Relation may be accounted for by social factors. 1999: BMJ. p. 1576.
3. O'Callaghan, MJ, GM Williams, MJ Andersen, W Bor, and JM Najman, Prediction of obesity in children at 5 years: a cohort study. 1997: J Paediatric Child Health. p. 311-316.
4. Dubois, L and M Girard, Early determinants of overweight at 4.5 years in a population-based longitudinal study. 2006: Int J Obes (Lond). p. 610-617.
5. Elliott, KG, CL Kjolhede, E Gournis, and KM Rasmussen, Duration of breastfeeding associated with obesity during adolescence. 1997: Obesity Research. p. 538-541.
6. Li, L, TJ Parsons, and C Power, Breast feeding and obesity in childhood:cross sectional study. 2003: BMJ. p. 904-905.
7. Maffeis, C, R Micciolo, A Must, and M Zaffanello, Parental and perinatal factors associated with childhood obesity in north-east Italy. 1994: Int J Obestiy. p. 301-305.
8. Padez, C, I Mourao, P Moreira, and V Rosado, Prevalence and risk factors for overweight and obesity in Portuguese children. 2005: Acta Paediatrica. p. 1550-1557.
9. Parsons, TJ, C Power, S Logan, and CD Summerbell, Childhood predictors of adult obesity: a systematic review. 1999: Int J Obes :. p. S1-S107.
10. Ravelli, ACJ, JHP van der Meulen, C Osmond, DJP Barker, and OP Bleker, Infant feeding and adult glucose tolerance, lipid profile, blood pressure, and obesity. 2000: Arch Dis Child. p. 248-252.
11. Salsberry, PJ and PB Reagan, Dynamics of early childhood overweight. 2005: Pediatrics. p. 1329-1338.
12. Owen, CG, RM Martin, PH Whincup, G Davey-Smith, MW Gillman, and DG Cook, The effect of breastfeeding on mean body mass index throughout life: a quantitative review of published and unpublished observational evidence. . 2005: Am J Clin Nutr. p. 1298-307.
13. World Health Organization., Obesity: Preventing and managing the global epidemic:  report of a WHO consultation on obesity. Geneva. 2000: WHO Technical Series No 894. http://whqlibdoc.who.int/trs/WHO_TRS_894.pdf.
14. Wang, Y, C Monteiro, and B Popkin, Trends of obesity and underweight in older children and adolescents in the United States, Brazil, China and Russia. 2002: Am J Clin Nutr. p. 971-7.
15. Davison, KK, LA Francis, and LL Birch, Re-examining obesigenic families: Parents' obesity-related behaviors predict girls' change in BMI. 2005: Obesity Research. p. 1980-199.
16. Lin, BH and RM Morrison, Higher fruit consumption linked with lower body mass index. 2002: Food Review http://www.ers.usda.gov/publications/FoodReview/DEC2002/frvol25i3d.pdf. p. 28-32.
17. OFCOM, Child obesity - food advertising in context. 2004: http://www.ofcom.org.uk/research/tv/reports/food_ads/.
18. Brettschneider, WD and R Naul, Study on young people's lifestyles and sedentariness and the role of sport in the context of education and as a means of restoring the balance. 2004: http://europa.eu.int/comm/sport/documents/lotpaderborn.pdf.
19. Jago, R, T Baranowski, JC Baranowski, D Thompson, and KA Greaves, BMI from 3-6 y of age is predicted by TV viewing and physical activity, not diet   Int. J. Obesity 29:557-565. 2005: Int. J. Obesity. p. 557-565.
20. Reilly, JJ, J Armstrong, AR Dorosty, PM Emmett, A Ness, I Rogers, C Steer, and A Sherriff, Early life risk factors for obesity in childhood: cohort study. 2005: BMJ. p. 1357-1363.69. 
21. Dewey, KG, Is breastfeeding protective against child obesity? 2003: J Hum Lact. p. 18.
22. Butte, N, The role of breastfeeding in obesity. 2001: Pediatric Clinics of North America. p. 189-198.
23. Heidiger, ML, MD Overpeck, WJ Ruan, and JF Troendle, Association between infant breastfeeding and overweight in young children.  285: 2453-60. 2001: JAMA. p. 2453-60.
24. Clifford, TJ, Breast feeding and obesity. 2003: Br. Med. J. p. 879-880.

Posted February 2007