A 12-week randomized trial found that whole-grain rye did not beat refined wheat for weight loss, but it did reduce inflammation and shift the gut microbiome and short-chain fatty acids in potentially beneficial directions.
Important points
Rye did not outperform wheat in terms of weight loss.
Rye reduced inflammation after 12 weeks
Rye altered gut bacteria and short-chain fatty acids in potentially beneficial ways
Starting metabolic state can influence response
Study: Effects of low-calorie whole grain rye and refined wheat diets on weight loss, cardiometabolic risk factors and gut microbiota: a 12-week randomized controlled trial. Image credit: Sham Clicks / Shutterstock
In a recent study published in the journal clinical nutritionDanish and Swedish researchers present the results of the RyeWeight2 study. This 12-week randomized controlled trial investigated whether replacing refined wheat with whole grain rye in a calorie-restricted diet led to greater weight loss and improved metabolic health.
The study results showed that both groups lost significant weight, but rye and wheat were statistically indistinguishable in terms of weight loss. However, we observed that a diet rich in rye resulted in significant reductions in biomarkers of systemic inflammation and favorable changes in the gut microbiota. The findings suggest that for people with pre-existing insulin resistance, rye may have additional metabolic benefits compared to refined wheat.
Obesity, whole grains, and dietary interventions
World health organizations posit that overweight and obesity are among the most pressing public health challenges facing society today, citing medical records suggesting that these metabolic conditions and their comorbidities contribute to millions of deaths annually.
Decades of research have aimed at reducing excessive weight gain (on a population scale) through dietary interventions. In this context, nutrition science promotes whole grain intake, citing consistent associations between whole grains and lower body fat and improved metabolic markers.
Previous research, including the original RyeWeight1 study, suggested that rye may specifically promote weight loss by improving appetite control and altering gut-derived metabolites. However, much evidence points to conflicting results, inconsistencies resulting from interindividual differences and a persistent lack of methodological standardization.
Randomized controlled trial design and methods
This study aimed to address the ongoing debate regarding the metabolic benefits of rye by evaluating the effects of whole grains on body weight, body composition, metabolic risk markers, and gut microbiota. The study (called ‘RyeWeight2’) recruited 255 overweight or obese adults (BMI = 27-35 kg/m²) to undergo 12 weeks of concurrent interventions. Study participants were randomly assigned to two groups (rye/experimental vs. wheat/control) in a 1:1 ratio.
Both groups were given a low-calorie diet designed to provide a daily energy deficit of 500 kcal. The rye group replaced their regular grains with whole grain rye products (giving them about 30g of fiber per day), while the other group used refined wheat products (giving them only 8g of fiber).
This study utilized a dual-energy X-ray absorptiometry (DXA) assay to measure changes (from baseline) in participants’ body fat and lean body mass. Additionally, shotgun metagenomics and blood biomarker assays were used to determine the DNA sequences of the participants’ gut bacteria and to analyze the blood samples for short-chain fatty acids (SCFAs), metabolic signaling molecules produced when fiber is fermented in the colon, revealing the participants’ gut microbial composition.
By the end of the 12-week study, DXA results analysis revealed significant weight loss in both groups. Participants in the rye group lost an average of 3.2 kg (7 lb), and participants in the wheat group lost an average of 2.9 kg (6.4 lb). However, these differences were not statistically significant (p = 0.32), meaning that rye did not outperform wheat in promoting weight loss in our sample cohort.
Inflammatory biomarkers and changes in gut microbiota
Of note, blood biomarker assays revealed a 17% reduction in C-reactive protein (CRP, a systemic inflammatory marker) in the rye group, but not in the wheat group (p = 0.03). Similarly, plasma butyrate (an anti-inflammatory SCFA) was observed to be 38% higher by week 12 in the rye group compared to the wheat group (p = 0.03).
Shotgun metagenomics supported these findings, showing that the rye diet was associated with significant increases in liver levels in participants. Bifidobacterium adolescentisa bacterium previously associated with improved glucose tolerance. Conversely, some microbial taxa are associated with adverse health effects (e.g. Ruminococcus torque) significantly decreased in rye consumers compared to wheat consumers.
Insulin resistance and individual response differences
Unexpectedly, statistical analysis found that participants with higher baseline Homeostasis Model Assessment of Insulin Resistance – Homeostasis Model Assessment (HOMA-IR) levels had poorer weight loss in the wheat cohort, and that baseline HOMA-IR and CRP were associated with changes in body weight and fat mass, suggesting that a whole grain diet may be particularly beneficial for individuals with high baseline insulin resistance and inflammation.
Clinical implications of rye diet research results
The RyeWeight2 study results indicate that although a whole-grain rye diet may not promote improved short-term weight loss compared to refined wheat-based diets, its effects on the gut microbiome and blood biomarkers may have a positive impact on cardiometabolic health.
Although the RyeWeight2 study failed to replicate the weight loss results of the RyeWeight1 study, the authors hypothesized that this discrepancy may be due to the fact that the current sample was slightly younger than the first study and demonstrated improved baseline insulin sensitivity, particularly in the wheat group.
However, current research suggests that rye has anti-inflammatory properties and may alter the gut microbiome in ways that may positively impact cardiometabolic health. The study did not find that baseline gut microbiota predicted weight loss after 12 weeks, nor did it show differences in subjective appetite between groups.
Future research should aim to investigate these benefits within the framework of “precision nutrition,” which uses a patient’s baseline inflammation and insulin markers to identify the most appropriate grains for a patient’s unique biology.
