Twenty-two primary studies (approximately 1,400 participants, range six to 272) were included in the review: 17 RCTs, three non-randomised trials, one case-control study and one cross-sectional study. Six studies examined change in maternal diet in breastfed infants (533 participants), 13 studies examined use of partially, extensively or completely hydrolysed formulae (517 participants), four studies examined the use of soy-based formulae (281 participants), one study examined the effect of a fibre-enriched formula (27 participants) and three studies examined the effects of carbohydrate alteration (40 participants). Fifteen studies were rated positive quality, three were rated neutral and four rated negative quality.
Three of the six studies that examined changes in maternal diet of breastfed infants found some beneficial effects of the mother changing to a hypoallergenic diet (two studies did not separate results from breastfed infants and results from infants fed hypoallergenic formula). Two studies that examined only elimination of cow's milk or dairy products, fish and eggs from the diet found no beneficial effects on colic; a cross-sectional study reported increased colic with consumption of cruciferous vegetables, cow's milk and onions, and no effect of garlic or chocolate.
The results from the 13 studies that examined partially, extensively or completely hydrolysed infant formula strongly suggested that these preparations can reduce symptoms of colic. All of the studies of partially, extensively or completely hydrolysed infant formula showed improvements in the intervention groups (such as reduced crying time, reduced colic symptoms).
All four studies of use of soy-based formula showed some improvement in the intervention groups. In one of the studies this was similar to the effect of partially hydrolysed formula. There were fewer symptoms of colic in studies of soy-based formula compared to cow's milk based formula; in one higher quality RCT the effect was relatively small.
One study compared fibre-enriched infant soy-based formula with soy-based formula only and found no significant difference on crying and fussing time.
One of the three studies of carbohydrate alteration did not report on infants with colic and another found that juices with poorly absorbed carbohydrates (apple) induced more crying in infants with colic than juices with readily absorbed carbohydrates (grape). There was no difference in infants without colic. In the third study there was no significant effect of pooled breast milk or cow's milk with hydrolysed lactose on colic duration compared to preparations without hydrolysed lactose.