There were also significant reductions in their low-density lipoprotein (LDL) cholesterol and total cholesterol levels as compared to the control group.
Legumes are plant foods and are rich in fibres. Examples include lentils, peas, and chickpeas.
The trial was conducted by researchers from National University of Singapore, Singapore Institute of Food and Biotechnology Innovation (SIFBI), Agency for Science Technology and Research (A*STAR), and Wilmar International.
Writing in Nature Communications, they pointed out that a multicomponent intervention, including a legume-rich diet, can improve metabolic health in prediabetic people.
A total of 127 Chinese prediabetic individuals from Singapore took part in the 16-week trial.
They were randomised to two groups, taking diets with lower calories - such as a lower intake of fats, sodium - and similar nutritional composition.
However, the intervention group’s diet consists of a significantly higher amount of dietary fibre due to the inclusion of 100 g of cooked legumes per meal. The legumes include mixed beans, red kidney beans and chickpeas.
Their body compositions, including weight, waist circumference, and body mass index (BMI) were measured, as well as their cholesterol and glycated haemoglobin (HbA1c) levels - which indicate their blood sugar levels.
Findings showed a a statistically greater decrease in HbA1c in the intervention group as compared to the control group.
For example, by week 16, the intervention group’s HbA1c was nearly four per cent lower, while that of the control group was about 2.5 per cent lower.
Other blood sugar related indicators, such as insulin and insulin resistance also went down, while fasting blood glucose remained stable over time.
Both groups also showed significant reductions in blood cholesterol, including total cholesterol, as well as both the “good” high-density lipoprotein (HDL) cholesterol and the “bad” LDL cholesterol.
However, the decrease in LDL and total cholesterol was greater in the intervention group, and the “good” cholesterol HDL subsequently went up in the intervention group.
“LDL-C and TC plateaued following a sharp decrease after week four. In contrast, HDL-C increased in a time-dependent manner after an initial decrease after week four,” the researchers pointed out.
Changes in body compositions
By the end of the study, both groups showed a significant decrease in their BMI, weight, hip, waist, and neck circumference.
On average, the intervention group lost 3.23 ± 0.18kg and the control group lost 2.7 ± 0.22 kg of their weight from baseline.
There were also a greater reduction in their fat mass as compared to lean mass.
“While there were reductions in both fat mass and lean mass, the total lean mass to total fat mass ratio significantly increased in both groups over time indicating greater relative reductions in fat mass compared to reductions in lean mass following the intervention,” said the researchers.
Changes in gut microbiota
The legume-rich diet has led to significant increases of certain bacteria species in the intervention group as compared to control group.
These species include Eubacterium rectale, Roseburia faecis, Roseburia hominis, as well as the Bifidobacterium genus under the phylum Actinobacteria.
Some of these species, such as Eubacterium rectale and Roseburia faecis were “negatively correlated” with total cholesterol and LDL-cholesterol.
This also explains why the intervention group had a significantly greater reduction in total cholesterol and LDL-cholesterol as compared to the control group.
On the other hand, the intervention group saw a decrease in species such as Ruminococcus gnavus, Ruminococcus torques, Bacteroides massiliensis, and Bilophila wadsworthia.
These are also species linked to diet lacking in fibre and were present in low amounts in individuals following the Mediterranean diet.
“This finding may imply that alterations in gut flora could be associated with enhanced lipid and blood glucose levels in individuals with pre-diabetes, potentially through diverse mechanisms,” said the researchers.
“Previous studies showed that bacterial species, such as Eubacterium rectale, Roseburia faecis and genus Bifidobacterium, are altered by fiber interventions, promote the growth of SCFA producers and confer health benefits such as reducing diabetes risk.
“Similarly in our study, greater reductions were observed in IG in species belonging to the genera Bacteroides and Ruminococcus, such as Ruminococcus torques, Ruminococcus gnavus and Ruminococcus lactaris.
“These species were previously linked to diet lacking in fibre and inversely associated with Mediterranean diet. They have been reported to be related to intestinal health impairments and metabolic dysregulations,” said the researchers.
Other than the increase and decrease in certain bacteria species in the intervention group, there were no changes in bacteria diversity in both groups by the end of the study.
The findings showed that food-based dietary interventions could be used reduce risks of type II diabetes and cardiovascular diseases, especially in populations with greater predisposition to such diseases, the researchers said.
“We have also demonstrated that the favourable effects on the cardiometabolic biomarkers may be mediated through the composition and function of the gut microbiome, although some of these associations need to be further validated in other independent cohorts,” they concluded.
Source: Nature Communications
A legume-enriched diet improves metabolic health in prediabetes mediated through gut microbiome: a randomized controlled trial
https://doi.org/10.1038/s41467-025-56084-6
Authors: Wu, X., Tjahyo, A.S., Volchanskaya, V.S.B. et al.
