This study examined the changes made in both GI and food costs following nutrition education regarding both the quality and type of carbohydrate for pregnant women. At the end of their pregnancies the low GI dietary intervention, had a significant decrease of GI from 55.1 to 51.6, which was similar to the result of a previous study by Moses et al in a comparable population [13
]. The GI was found to have a mean of 55.1 at the start of the study, which is lower than the average dietary GI being reported in Australia as between 56 and 58 [19
]. This comparatively lower initial GI value may be attributed to an increase in the consumption of dairy, fruit and wholegrain products, which has been identified as the dietary changes commonly made by pregnant women [20
]. Miller et al.
] also identified a change in GI with participants with type 2 diabetes after receiving nutrition education, with a substantial change in the consumption of whole fruit, non-fat dairy products and vegetable fat. The change in food cost based on individual food groups was not examined. Our results also suggest that it is possible to lower dietary GI without incurring additional cost to the pregnant women. While, to our knowledge, there has been no previous studies relating to the cost of changing to a low GI diet following low GI diet advice, the literature related to costs and food choices is by no means consistent.
Cross sectional studies found higher energy diets cost less whereas lower energy diets cost more [8
]. A market basket survey study by Jetter et al.
] revealed healthier market baskets to be significantly more expensive, primarily due to higher costs of wholegrains, lean ground beef, and skinless poultry. Similarly, Drewnowski et al.
] and other researchers have also revealed through cost analyses that diets rich in fat and sugar are more affordable than diets high in fruits and vegetables [25
]. Many of these studies utilise cost per calorie (or mega joule) comparison which can cause a two thousand calorie diet of fruit and vegetables (low energy dense, high nutrient) to be more expensive than that composed of high fat, high sugar foods (energy dense, low nutrition).
Our study is more in line with the findings of longitudinal intervention studies, where dietary advice and intervention has been provided to specific groups. Mitchell et al.
] who examined the food costs in low fat diets of obese children found that there was no significant difference in food costs between the low fat diet and a control group. Moreover, Rydén et al.
] compared a Mediterranean diet to a standard Swedish diet and found no significant differences in non-energy adjusted costs between diets. Other researchers who have conducted cost benefit analyses of nutrition education programs have also found a significant decrease in spending after receiving nutrition education and advice [32
]. It has been suggested that the differences in findings, can be attributed to the longitudinal examination of the data, rather than cross sectional, suggesting that over time, different food choices and cooking methods may be adopted that allow for lower food costs [34
]. In contrast, women in a UK study indicated that a low fat diet increased costs due to an increase of fruit and vegetables but attributed this to the purchase of more expensive organic foods. They also acknowledged that at least half of the participants stated that it wasn’t difficult to eat healthily [26
The purchase and consumption of products branded specifically as “low GI” is a factor which must be considered when examining the cost of following low GI dietary advice. While low GI products are available in many natural food sources, products developed and labelled as low GI such as low GI, Hi-Fibre breads may provide an easy choice for those following a low GI diet, and may incur additional costs. This finding was not found with our study, and could possibly be attributed to the support and nutrition advice provided on how to purchase low GI foods without the added expense. Similar findings have also been found with participants attending a healthy eating program who saved significantly more when receiving nutrition education when compared to a group that did not receive nutrition education [32
]. Raynor et al.
] also found that after families had received nutrition education that total daily food cost did not change at 6 months and decreased significantly at 12 months.
Limitations of our study must be considered when interpreting the findings. Three-day food records are susceptible to known biases. Our study also had to assume that all foods, unless specified otherwise, were purchased within the supermarket. Additionally, some foods such as out of season fruit and vegetables were unavailable on the day and had to be priced as an average price for that product. General assumptions were also made about recipes and the ingredients used in these recipes. As prices were recorded only on one day they may differ from original prices paid due to daily price fluctuations.
A supermarket cost analysis was conducted rather than using online supermarket websites, national retail/food price surveys, nutrient databases or shopping catalogues, to allow for the maximal variety of foods from the food records to be priced and to emulate the most realistic means of shopping amongst Australian women. A major supermarket in Wollongong was chosen as the location for the cost analysis as the price of a food basket in Wollongong has been identified to being close to that of the average price of a food basket across supermarkets located in five suburbs within the region [24
]. However, prices obtained at Woolworths Wollongong may not necessarily be representative of food prices in other parts of Australia.
The participants of the PREGGIO study following the healthy rather than the low GI diet were not included in this study for cost analysis before and after dietary education, due to resource constraints. Although the GI did not significantly decrease in this group, we are unable to say whether food costs increased or decreased after seeing the dietitian for healthy eating education for pregnancy. However this is certainly an area for future research from the database of the major study.