Unit 2: Health Effects of Complementary Feeding

The development of immune tolerance is a critical process early in life. It appears that these tolerance pathways are susceptible to environmental changes which is evident by the rising rates of allergic and autoimmune diseases. Many of these conditions, including food allergies, celiac disease, and type 1 diabetes develop early in life, however the mechanisms remain unclear (Prescott et al. 2008).

Immune tolerance appears to occur at the same time as the development of healthy gut colonization, which is essential in promoting tolerance to allergens (Sudo et al. 1997). Failure of oral tolerance can occur if there are delays in either colonization or antigen/allergen exposure (Norris et al. 2005; Poole et al. 2006).

However, the risk of allergic or autoimmune disease may increase if  allergen exposure occurs too early (Halken & Host 1996). Furthermore, some studies have suggested that the continuation of breastfeeding while introducing complementary foods is crucial for promoting tolerance (Ivarsson et al. 2002). Please refer to unit 4 for further information on gut development.

The timing of this “critical early window” to prevent allergies is not completely clear, however current evidence suggests that it may be between the 4th and the 7th months of life, and late exposure to complementary food beyond this time may actually increase the risk of food allergy (Prescott et al. 2008).