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Updated: Jan 5, 2023

The Effect of Rye-Based Foods on Postprandial Plasma Insulin Concentration: The Rye Factor

Consumption of whole grain has been associated with lower incidence of type-2 diabetes, cardiovascular disease and their risk factors including improved glycemic control. In comparison with other whole grain products, rye bread has been shown to induce lower insulin response in the postprandial phase, without affecting the glucose response. This phenomenon has been referred to as the “rye factor” and is being explored in this review where we summarize the findings from meal and extended meal studies including rye-based foods.

Overall, results from intervention studies showed that rye-based foods vs. (wheat) control foods had positive effect on both insulin and glucose responses in the postprandial phase, rather than on insulin alone. Mechanistic studies have shown that the rye factor phenomenon might be due to slowing of the glucose uptake in the intestine. However, this has also been shown for wheat-based bread and is likely an effect of structural properties of the investigated foods rather than the rye per se. More carefully controlled studies where standardized structural properties of different cereals are linked to the postprandial response are needed to further elucidate the underlying mechanisms and determinants for the effect of specific cereals and product traits on postprandial glycemic control.

Low grade inflammation, a known risk factor for development of cardiovascular disease, has in several studies been shown to be reduced by consumption of whole grain rye products. A recent study from Chalmers has shown that this may be explained by changes to the bacteria in the gut.

The study showed the participants who consumed rye products for 12 weeks had a lower concentration of C-reactive protein, a common marker of inflammation, in their blood compared to participants who consumed refined wheat products. Furthermore, certain bacteria in the gut, that are known to affect inflammatory response, was reduced in the rye group. These results indicate the health effects of rye may in part be explained by the effect rye has on bacteria in the gut.

The 12th of September 2020, Adila Omar defended her doctoral thesis from Karolinska Institutet on ‘Dietary carbohydrate quality and health – focus on low-grade systemic inflammation and cardiometabolic risk factors´ . Image from: Chalmers University of Technology.

Dietary carbohydrate quality, characterized by content of whole grain (WG), dietary fiber, and sugars, is important for human health. Whole grain consumption and cereal fiber can reduce the risk of chronic disorders such as cardiovascular disease (CVD) and type 2 diabetes, an effect partly mediated by alterations in cardiometabolic risk factors and low-grade systemic inflammation. High-fructose or high-galactose diets may trigger pro-inflammatory and negative metabolic effects, but fermentable dietary fiber, e.g., fructooligosaccharides (FOS), may mitigate these effects. This thesis examined the effect of dietary carbohydrate quality, characterized by intake of specific WGs and sugars, on low-grade systemic inflammation and cardiometabolic risk factors. In particular, it evaluated: 1) associations between long-term WG rye or wheat intake and inflammatory, endothelial function, and CVD risk-related biomarkers; 2) alkylresorcinols (AR) in adipose tissue as potential biomarkers of long-term WG intake; 3) effects of WG/bran rye and refined wheat on inflammatory and endothelial function biomarkers in individuals with low-grade prostate cancer; and effects of high fructose and galactose intake, with or without added FOS, on 4) selected metabolic factors and inflammatory and gut permeability biomarkers; and 5) modulation of gut microbiota in rats.

Data and samples from two prospective cohort studies, Swedish Mammography Cohort-Clinical (SMC-C) (n=109) and Cohort of Swedish Men-Clinical (COSM-C) (n=149), were used to analyze associations between long-term WG intake and selected biomarkers of inflammation, ndothelial function, and metabolic factors. WG intake was assessed by food frequency questionnaires and using alkylresorcinols (AR) in plasma and adipose tissue as biomarkers. Combined WG rye and WG wheat intake was positively associated with cathepsin S, while total AR in plasma was inversely associated with endostatin (adjusted for age, sex, and BMI). Long-term WG rye intake was modestly correlated (r=0.31-0.41) with AR in adipose tissue, whereas WG wheat was poorly correlated (r=0.17-0.33) over 14 years for men and 17 years for women. The effect of WG/bran rye on selected inflammatory biomarkers was explored in a dietary intervention cross-over study of 17 men with low-grade prostate cancer. TNF-R2, e-selectin, and endostatin were significantly lower in these men after consumption of WG/bran rye products than consumption of refined wheat with added cellulose. In an animal study with rats (n=6/group and time point) fed a high-fructose or high-galactose diet, with/without added FOS, or three control diets for six or 12 weeks, the intervention diets affected several metabolic factors and gut integrity markers, but not inflammation biomarkers. High-fructose and high-galactose diets did not cause substantial changes in gut microbiota composition, but addition of FOS favored the genus Bifidobacterium. Gut microbiota was associated with several metabolic and inflammation biomarkers.

These results suggest that WG wheat and rye may have positive impacts on some inflammation biomarkers. Fructose and particularly galactose had adverse metabolic effects in rats, but no obvious effect on inflammation markers. Sugars did not markedly affect gut microbiota composition in rats.

Main supervisor:

Rikard Landberg, Professor, Department of Biology and Biological Engineering, Division of Food and Nutrition Science, Chalmers University of Technology.


Professor Alicja Wolk, Karolinska Institutet Institute of Environmental Medicine Unit of cardiovascular and Nutrition Epidemiology

Associate Professor Galia Zamaratskaia Swedish University of Agricultural Sciences Department of Molecular Sciences

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