The present study investigated for the first time how whole grain crisp bread instead of refined wheat bread for breakfast affected the self-reported hunger, satiety and desire to eat as well as the energy intake after a subsequent meal served ad libitum 4 h after breakfast. Effects were evaluated in two studies where the amount of test foods as well as the total energy intake of the breakfasts differed.
In Study one, where test bread intake as well as total energy intake was relatively high, participants felt less hungry and less desire to eat after consuming RB instead of WB for breakfast. However, no statistically significant effect on fullness or in energy intake after a subsequent lunch was observed. The bread portion together with the additional breakfast foods comprised what would be considered a large breakfast (2480 kJ)
. Due to the large surface area of crisp bread, more spread, ham and/or cheese was needed than for a typical soft bread of similar weight.
The amount of breakfast product and the total energy intake was reduced in Study two, in order to investigate whether more consistent effects on appetite and subsequent meal energy intake could be obtained at a somewhat lower intake of product and lower total energy intake. The difference between treatments in Study two was similar in magnitude (20-28%) as in Study one, but more consistent as a statistically significant difference in self-rated satiety was also found.
Although the amount of test bread used in Study two was 20% lower than in Study one, the proportion of energy from test bread of entire breakfast was higher since the total energy of the entire breakfast was considerably reduced. The total energy in Study two was in the lower range (1580 kJ) of what would be considered a normal breakfast
. We speculate that the less consistent results in Study one compared with Study two were due to a too high over-all breakfast intake and/or energy intake which masks differences between tested breads due to the fact that participants reported high satiety ratings for both diets. This is to some degree supported by results from previous studies
[15, 16]. However, the macronutrient composition differed slightly between our our two studies and that could also have affected the results.
The finding that whole grain rye crisp bread affects satiety, hunger and desire to eat as well as energy intake in a subsequent meal, in a favorable direction is in line with previous studies with fibre-rich rye products in a similar study design. Isaksson et al. have for example consistently shown that whole grain rye porridge based on intact kernels, different milling fractions and flour or flakes, increase satiety and decrease hunger during 4 h after intake, compared with iso-caloric refined wheat bread served with identical breakfast foods
[16, 17, 31]. Also iso-caloric rye breads containing different bran fractions, whole grain, and sifted rye flour, all showed significantly higher satiety ratings than refined wheat bread although the largest effects were observed when replacing 25-60% of the refined wheat flour for rye bran
. Furthermore, Rosén et al.
 found similar effects on appetite ratings for different rye breads for breakfast compared to a refined wheat bread breakfast and they also found 16% lower energy intake at lunch when participants consumed rye kernel bread compared with refined wheat bread. These findings are in line with the 8% lower energy intake at lunch after RB compared to WB breakfast in present Study two.
In our two studies, we found no significant difference between the two test breads at the first time point (30 min) after breakfast. This is in contrast to what has been found in the studies with rye bread and porridges by Isaksson et al.
[15, 31], where differences between treatments started to appear immediately after intake. This difference between studies probably reflect the higher water content in soft bread and porridge which results in a larger volume compared to crisp bread. Added water incorporated into foods has been shown to increase satiety and decrease spontaneous food intake in short-term
. Isaksson et al. showed that the immediate effect of large difference in weight and volume caused by water between a milled kernel porridge and a kernel porridge, disappeared during the first hour after a meal
In the current study we only evaluated effects up to 4 hours. In previous studies, prolonged satiety between 4.5-8 h after breakfast has been observed after consumption of rye porridge with intact kernels, but not milled kernels, probably as a result of reduced small intestinal digestion and absorption due to a physical barrier to digestive enzymes and hence, a greater extent of nutrient and dietary fibre reached the colon where they could be fermented
. However, high-fibre breads based on milled rye bran and whole grain flour also showed significantly higher degree of dry matter, ash, protein, fat, amylase-available starch and dietary fibre escaping small intestine digestion and in an ileostomy model
. This suggests that rye products based on milled flour, may also lead to a greater availability of fermentable nutrients in the colon, which could affect satiety and appetite. RB contained more fermentable fructans and arabinoxylans than the WB. It remains to test whether whole grain crisp bread also results in significant afternoon effects.
We did not assess the mechanisms underlying the beneficial effects of replacing WB for RB in the present study. However, it is interesting that RB, which has a smaller volume and different microstructure than soft bread or porridge resulted in similar effects on self-reported appetite ratings and reduction in energy intake
[15–18, 20, 31]. This suggests that features of dietary fibre and or bioactive compounds of rye may be more important for the short-term effect (≤ 4 h) on self-rated appetite and energy intake than for example test product volume. The dietary fiber intake in the present study was higher or similar compared with previous studies using high-fiber rye products
[15–18, 20, 31]. Positive effects on appetite derived from rye fiber may include bulking effects resulting in increased extension of the stomach and delayed gastric emptying (for viscous fiber) which in turn may affect nutrient absorption kinetics. High-fibre rye compared to refined wheat has been shown to lower postprandial insulin secretion
[19, 21]. This together with other early signals of satiation may have contributed to positive effects appetite ratings in the present study. The impact of bioactive compounds such as benzoxazinoids and phenolic acids on glycemic response appetite has been investigated recently, but needs to be studied further to reach a conclusion
Taken together, results from the studies clearly showed beneficial effects of eating whole grain rye crisp bread compared with refined wheat bread as part of a normal breakfast on hunger, desire to eat and/or satiety. The difference was about 20-30% between treatments and the effects are most consistent when RB constituted a large proportion of the energy content of a small breakfast.