From the discussion above, it appears that nutritional alterations during the suckling period alone can significantly increase the risk for the development of metabolic disorders in adulthood (fig. ). This observation has a direct impact on infant feeding practices with specific reference to reduced rates of breastfeeding and early introduction of complementary foods. The American Dietetic Association has suggested that infants should be exclusively breastfed for the first 6 months of life and that complimentary foods should be introduced only after 6 months of age [65
]. Breast milk has the ideal combination of nutrients, hormones and other factors essential for the proper development of babies. The beneficial effects of breastfeeding for the infant are well documented. For example, it has been shown that breastfeeding was associated with a reduction in the risk for obesity, and type 1 and 2 diabetes, etc. [66
]. On the other hand, increased height and weight gains and adult-onset obesity have been reported in infants who were only formula fed in their infancy [67
]. Shorter periods of breastfeeding and early introduction of complementary foods have been shown to result in altered growth patterns in infants [69
]. A recent report on the analysis of data from five cohorts in low- and middle-income countries after adjusting for confounding factors showed that later introduction (after 6 months) of complementary foods was associated with lower body weight in adulthood [70
Based on animal studies and observations in humans, malprogramming and nutritional alterations during early postnatal life could significantly increase the risk for development of metabolic disorders in adulthood. ANS = Autonomic nervous system.
Although breastfeeding for infants has been advocated by the responsible authorities, dietary practices for infants have undergone major changes. In the first half of the 20th century, formula feeding for infants began to gain popularity with a concomitant decrease in breastfeeding rates and early introduction of complementary foods [68
]. The impetus for the promotion of formula feeding has been attributed to commercial interests and changes in public health policies [71
In addition to reduced breastfeeding rates and increased rate of formula feeding, there appears to be a disturbing trend with regard to early introduction of complementary foods. It can be seen from table that complementary foods for babies are mostly carbohydrate dense (mainly simple sugars) and include fruits, fruit juices and vegetables. Table indicates the reciprocal changes in carbohydrate-derived calories and fat-derived calories in the total available calories for infants when milk (human or formula) is supplemented with complementary foods. At the level of 30% supplementation, there is a marked increase in carbohydrate-derived calories and a marked decrease in fat-derived calories. Since babies receive such foods via the bottle and spoon, there is a possibility of over-feeding babies due to these modes of feeding. This could further increase the carbohydrate load for the babies. As observed in the HC rat model, substantial increases in the availability of carbohydrate-derived calories during infancy could predispose these infants to overweight and obesity in their later life.
Total calorie content and calories derived per serving from carbohydrate, protein and fat for some of the popular commercially available first foods for babies
Estimation of the increased intake of carbohydrate-derived calories by infants due to early supplementation (prior to 6 months of age) of milk (human or formula) with baby first foods without increase in daily total calorie intake
Although it has been shown that consumption of sugar-enriched drinks increased the risk for overweight/ obesity and other diseases [72
], the WIC (Women, Infants and Children) Infant Feeding Practices Study found high levels of consumption of sweet drinks (e.g. sugar water or fruit-flavored drinks) by infants. In the first month of life, 14% of infants received these drinks; by 4 months, about 30% were given these drinks. This practice was predominant amongst Hispanic infants [73
]. Further, it was noted that a large number of infants received fruit juice earlier than the recommended age of 6 months – about 50% by the age of 4 months [73
]. Based on the observations on the HC rat model, it is possible that early introduction of sugar-dense complementary foods for babies could be a contributing factor in the etiology of obesity in children and adults.
Accumulated evidence shows that the consequences of an early life nutritional challenge could be exacerbated by dietary practices in adult life. As an example, it has been noted that SL mice overnourished during the suckling period demonstrated increased body weight gains on a high-fat diet in the post-weaning period compared to SL mice weaned onto laboratory chow [32
]. It is possible that the metabolic adaptations occurring in infants due to early introduction of sweetened foods (before the recommended age of 6 months) could be amplified by consumption of calorie-dense foods in their later life. Such a situation could result in the development of obesity at an earlier age and to a greater extent.