Whole grain rye fails to outperform refined wheat in key metabolic markers
A new study found no meaningful difference in hunger hormones, blood sugar control, or inflammation between whole grain rye and refined wheat diets in overweight adults—challenging assumptions that underpin multibillion-dollar health food marketing claims. The finding suggests the relationship between grain type and metabolic health may be more complex than commonly promoted.
Originaltitel: Postprandial Effects of Four Test Meals Containing Wholegrain Rye or Refined Wheat Foods on Circulating Incretins, Ghrelin, Glucose, and Inflammatory Markers
<p>Background</p><p>High intake of whole grains has consistently been associated with reduced risk of obesity, coronary artery disease, and type 2 diabetes. Dietary interventions have shown beneficial metabolic effects of whole grains, but the metabolic response varies with different types of cereals.</p><p>Objectives</p><p>We evaluate the metabolic effects of substituting refined wheat with wholegrain rye foods within a complex diet, examining the day-long postprandial response of glucose-dependent insulinotropic peptide (GIP), glucagon-like peptide-1 (GLP-1), ghrelin, glucose, and inflammatory biomarkers in individuals with overweight and obesity.</p><p>Methods</p><p>Twenty-nine healthy adults with body mass index of 32 ± 9 kg/m<sup>2</sup> were randomly assigned to 3 intervention days, separated by 1-wk washout. Participants adhered to a hypocaloric diet rich in wholegrain rye for 1 intervention and refined wheat for the second intervention and were randomly assigned to either diet for the third intervention with continuous blood sampling.</p><p>Results</p><p>No differences in GIP, GLP-1, or ghrelin levels were found between the diets when measured throughout the whole intervention day. GIP total area under the curve after the rye-based lunch was 31% (<em>P</em> < 0.05) lower compared with the wheat-based lunch, and ghrelin concentrations were 29% (<em>P</em> < 0.05) lower after the rye-based dinner. Baseline Homeostatic Model Assessment for Insulin Resistance-adjusted model showed 61% (<em>P</em> = 0.015) lower whole-day GLP-1 and 40% (<em>P</em> = 0.03) lower GIP after the rye-based diet. Day-long glucose incremental area under the curve was 30% (<em>P</em> < 0.001) lower after the rye-based diet, and glycemic variability was measured as SD reduced (−0.13 mmol/L, <em>P</em> = 0.04). The rye-based diet compared with refined wheat induced higher glycoprotein N-acetylation A, as measured by z-scores (0.36, <em>P</em> = 0.014).</p><p>Conclusions</p><p>Overall, no day-long differences in gut hormone levels were observed, but the wholegrain rye-based compared with refined wheat-based dinner showed lower postprandial ghrelin concentrations. The rye-based diet improved day-long glycemic control in individuals with overweight and obesity. Observations of diet-induced inflammation after whole-grain rye intake warrant further investigation.</p><p>Trial registration number</p><p>This study was registered at Clinical Trials Registry of clinicaltrials.gov (NCT05004584): https://clinicaltrials.gov/study/NCT05004584?locStr=Gothenburg,%20Sweden&country=Sweden&state=V%C3%A4stra%20G%C3%B6taland%20County&city=Gothenburg&distance=50&term=appetite&aggFilters=status:com&rank=1</p>