To our knowledge, this is the first study comparing food costs of children and adolescents on a vegan, vegetarian and omnivore diet based on reports of self-selected diets and retail prices. Our data showed that the vegetarian diet was the most inexpensive dietary pattern, independent from TEI. In all diet groups, starchy foods, fruit, sweet foods, beverages, and vegetables contributed the most to daily costs. For omnivore participants, meat/fish also made a significant contribution. Protein foods, i.e., the sum of legumes/nuts, dairy alternatives, meat alternatives, dairy (vegetarian and omnivores only) and meat/fish (omnivores only), contributed a quarter of the total food costs, independent from diet group. The share for dairy alternatives of vegans in the total costs corresponded to the share of dairy products for omnivores.
Total daily food costs
According to our study, families had to spend 2.52 € − 2.98 €/1000 kcal a day on food for each child. The above mentioned evaluation using a similar approach with food prices from 2009 calculated food costs 1.84 € − 2.00 €/1000 kcal for omnivore children and adolescents . Thus, the food costs calculated in this study were considerably higher, independent from the dietary pattern. Similar to our findings, a recent study in Germany investigating food costs of four week sample menus using minimum retail prices estimated food costs per day of 5.17 €/day (2.59 €/1000 kcal) and 5.69 €/day (2.85 €/1000 kcal) for 10–13 year old girls and boys on a vegetarian diet, respectively. There, food costs of a vegan diet were about 1 €/day higher (6.17 €/day for girls, 6.97 €/day for boys) . The higher estimated total daily food costs in this study may be due to a higher assumed energy requirement (PAL 1.6, i.e., 2000 kcal/day for girls, 2200 kcal for boys). In the VeChi Youth Study, the TEI corresponded to the energy requirement with a PAL of 1.4 . Energy requirements and thus the amount of food needed is the most important determinant of total food costs . Therefore, daily food costs increase with age and are higher for boys than for girls [8, 32]. That is why the present evaluation considered food costs standardised to energy intake.
Both total daily food costs and standardised total food costs differed between the diet groups and showed a small but statistically significant benefit of vegetarian diets. Our results thus confirm the above mentioned German study from 2009, in which a vegetarian diet was associated with lower food costs in adult women than a diet that included the consumption of meat and fish . Besides, in the aforementioned study on food costs of sample menus a vegetarian pattern (as well as an omnivore diet consisting of fresh food) was the most inexpensive pattern. A vegan diet was estimated to be more expensive . However, total daily cost differences in our study were only small: The median total daily food costs of the omnivore and the vegan diet exceeded the daily food costs of a vegetarian diet by 0.31 €/day and 0.46 €/day, respectively. Per month, this results in a total difference of 9.30 € and 13.80 €. Nevertheless, for socially disadvantaged families or families with several children, these differences can be decisive for the choice of diet. However, it should be noted that the difference between the total daily food costs of vegan and omnivore diets was not statistically significant. Hence, a change from an omnivore diet to a more sustainable vegetarian diet could save money.
Furthermore, the wide interquartile ranges of energy standardised food costs in all diet groups are worth to mention (vegetarian participants: 1.04 €/1000 kcal, vegan participants: 1.01 €/1000 kcal and omnivore participants: 0.94 €/1000 kcal). Hence, food costs of the dietary patter overlap and there is a financial margin to make each diet pattern more inexpensive. Hence, a shift towards a vegan diet should not cause necessarily any additional costs.
Food group costs
The total daily food costs of a diet are partial determined by the amounts of food groups consumed. Because changes in the consumption of food groups, such as a shift from animal source to plant foods, also affect the consumption of other food groups, it is not possible to identify single food groups responsible for the observed differences in daily costs .
Starchy foods had the highest budgetary demand in our sample in the vegetarian and vegan group. This reflects the high contribution of this food group to TEI .
The high share of fruit and vegetables costs confirm the current state of the literature [3, 32], in particular when expressed as costs per calorie . However, this calorie-based approach does not take into account that consumers do not only buy food to meet their energy needs, but also for other reasons, such as individual preferences in taste or health aspects.
Sweet foods were also relevant for the energy and food cost shares. Vegans had significantly lower cost shares for this food group (11%) than participants of the other two diets (14% each). This can be attributed to the lower consumption of sweets compared to omnivore and vegetarian participants . In the aforementioned German modelling study , on the other hand, the cost shares of the food group snacks and sweet foods were 3% in a vegan diet, but only 1% in a vegetarian diet, which can be attributed to the fictive nature of the sample menus.
Dairy was consumed less by participants on a vegetarian diet than on an omnivore diet . That is why vegetarians spent less money on this food group than omnivores. Instead, vegetarians also spent 5% of their daily food costs on dairy alternatives, vegans 8%. Both vegetarians and vegans spent less money on meat alternatives than omnivores for meat, although energy standardised costs of meat alternatives are higher than of meat.
Meat, fish and eggs as well as dairy account for substantial food cost shares in omnivore diets [3, 32, 34]. As these foods are important sources of nutrients, it is recommended for vegetarian and vegans to increase the consumption of soy, legumes, nuts and seeds to provide protein, iron and zinc sufficiently . The nutrient profiles of meat alternatives and dairy alternatives are not comparable with the original animal-derived foods, and the nutrient content is variable depending on the ingredients used . In a direct price comparison (€/100 g), they are often more expensive. Nevertheless, in the VeChi Youth Study, costs for meat were comparable to the sum of costs for, i.e., legumes/nuts and meat alternatives in vegans. Willits-Smith et al.  even predicted a food cost reduction of 10% when replacing meat by legumes, seeds, nuts and soy foods in a New Zealand modelling study.
Besides food group intake, also food choices within a group, for example the type of fruit or vegetable or the degree of processing, affect food costs. That is why it can be argued, that cost estimates based on real-life data are more valid than cost estimates based on sample menus or modelling studies. In the VeChi Youth Study, omnivores differed significantly from vegetarians and vegans in terms of daily beverage costs. This food group even accounted for the largest share of costs next to sweet foods in an omnivore diet. This can be explained by the fact that vegan but also vegetarian study participants consumed more inexpensive beverages such as tap water, while omnivores more often consumed expensive bottled water and soft drinks. Regarding the total costs for processed foods such as convenience foods, meat alternatives etc. vegans showed the highest values, which also contributed to the higher daily total costs.
Another important aspect of food selection is the distinction between conventional and organic produced foods. Organic food, as well as animal source food assuring special animal welfare, are more expensive than conventional food products . About a quarter of the study participants in the VeChi Youth Study who followed a vegan or vegetarian diet reported buying more than 75% organic food, but only about 12% of those following an omnivore diet . In our survey, we could not distinguish whether unprocessed foods, e.g., fruits, vegetables or starchy foods, were from organic or conventional production. However, price collection of special brands considered the production procedure. The associated price effects may contribute to the observed differences in food costs.
Strengths and limitations
The present analysis has some methodological strengths and limitations that need to be discussed. As mentioned before, a cost calculation based on real-life consumption data yields more plausible cost estimates than a calculation based on sample menus.
Another important strength is the detailed brand-specific dietary survey, which enabled a very accurate and diet group-oriented price survey.
Our price survey conducted in different supermarkets should provide a representation of food prices as comprehensive as possible. A limitation of our method is the short time span of the survey, which does not capture seasonal effects, e.g., for the price of vegetables and fruit. In addition, the survey of all 2,866 food items recorded in the food logs was not feasible within the framework of this project. However, the present approach is a proven method for calculating food costs [8, 27]. Moreover, due to the covid pandemic and the resulting lockdown measures, a price survey was only possible online. A price survey in stationary retail might have led to slightly different total daily food costs. However, this is a random error that affects all diet groups equally. The effect of food price differences on total costs was excluded in this evaluation, as minimum prices were used.
A further limitation is the lack of representativity of the study sample. The high SES of most participating VeChi Youth Study families are consistent with the known sociodemographic characteristics of vegetarians and vegans . Although statistical models were adjusted for self-reported SES, some residual confounding cannot be excluded and the limited generalisability of the results must be kept in mind when interpreting them.
Last but not least, it should be mentioned, that we only assessed direct food costs, but did not consider further cost associated with nutrition, e.g. costs for purchase, storage or preparation.