Each year, a significant number of pregnant women around the world develop gestational diabetes mellitus (GDM), defined as glucose intolerance or high blood glucose concentration (hyperglycaemia) that starts or is first recognised during pregnancy. Women with GDM are at risk of having instrumental birth and their babies are more likely to be large for gestational age, have a birthweight of at least 4000 grams and experience birth trauma. Although it is widely accepted that dietary counselling is the main strategy for managing women with GDM, it is not clear which dietary therapy is best. The aim of this review was to assess the effects of different types of dietary advice for women with GDM looking at pregnancy outcomes. A total of nine small randomised trials involving 437 women (444 babies), with outcome data available for 429 women and 436 babies were included in this review. Eleven different types of dietary advice were assessed within six different comparisons, including low- or moderate- glycaemic index (GI) diet compared with high- or mixed-GI diet, low-GI diet compared with high-fibre, moderate-GI diet, energy-restricted diet compared with no energy restriction diet, low-carbohydrate diet compared with high-carbohydrate diet, high-monounsaturated fat diet compared with high-carbohydrate diet, and the standard American Diabetes Association diet providing 20 grams fibre per day compared with fibre-enriched diet providing 80 grams fibre per day. Based on the current available data, we did not find that any one type of dietary advice was more effective than others in reducing the number of births that required instrumental delivery or the number of babies who were large for gestational age or had a birthweight of 4000 grams or more. The included trials had various levels of risk of bias and it remains unclear which diet is the most suitable diet for women with GDM for improving the health of women and their babies in the short and longer term. Larger, well-designed randomised trials are needed.