Bread Replacement - Facing the Challenge to Improve Its Quality for Better Metabolic Health

Carbohydrates are the main source of energy in most European countries with intakes ranging from 40-60% of total energy. Consequently, the role of its quality and quantity for the development of metabolic diseases is the focus of substantial debate. Notwithstanding, replacing processed carbohydrates with unprocessed carbohydrates is regarded as a major strategy to improve public health. This is to a substantial degree based on strong observational evidence that higher intakes of dietary fiber (cereal grains containing the same relative proportions of bran, germ, and endosperm as the intact caryopsis) are associated with lower risks of total mortality, cardiovascular morbidity, and mortality, type 2 diabetes mellitus (T2DM) incidence and cancer mortality. Nonetheless, data from medium- to long-term intervention studies among adults are less conclusive regarding the benefits of whole-grain consumption on glycemic control, bodyweight and serum lipids. In fact, benefits may be largely confined to whole grains stemming from oats or barley, calling for explicit consideration of these whole grains and/or its mechanistically relevant component.

Adding complexity, many commonly consumed whole grains or products rich in dietary fiber are characterized by a high glycemic index (GI>70), in fact, a high dietary fiber content will not predict a low glycemic response. The GI describes the glycemic potency of the available carbohydrates in a food, is measured under defined conditions and is used to calculate the glycemic load (GL: GI x amount of available carbohydrates). Preferred consumption of high GI grain products is of concern since a higher dietary GI and GL may be causally linked to a substantial increase in T2DM risk and may translate into a considerable health burden.

In European societies, T2DM prevalence is increasing as a result of higher overweight and obesity rates and increases in longevity. Efforts are hence needed to develop carbohydrate-based food items that are both rich in fiber and whole grain and have a low GI and tailored to the dietary habits of middle-aged adults with insulin resistance (also called 'pre-diabetes' or intermediate hyperglycemia defined by intermediately increased HbA1c levels). This stage precedes clinical T2DM and affects up to 30% of adults in Western societies.

Enrichment with selected fibers, e.g. beta-glucan from oat and barley, may offer an alternative to whole grain kernel breads, which may not meet consumer preferences and is also endorsed by EFSA health claims. Preliminary small-scale studies indicate acute, short- and longer-term benefits of such bread for glycemic and/or insulinemic responses among persons with T2DM or at risk of T2DM. However, these studies suffer, besides the small sample sizes, from high amounts of test food (8 servings per day = 320 g bread) and use of white bread as a comparator. The present study will test whether habitual consumption of a bread containing oat bran concentrate and meeting the high beta-glucan content of the EFSA claim (4.3 g beta-glucan per 30 g available carbohydrate) compared to normal wheat bread high in whole grain but without kernels will affect glycemic control over a period of 16 weeks.

Main hypothesis The main hypothesis of the study is that bread enriched with beta-glucan will have a positive effect on blood glucose control (HbA1c) in persons with intermediate hyperglycemia.