Lentils lower cholesterol and sugar response, study finds

In a recent article published in the journal Nutrients, researchers evaluate the impact of 12 weeks of regular lentil consumption on metabolic health. 

Study: Twelve Weeks of Daily Lentil Consumption Improves Fasting Cholesterol and Postprandial Glucose and Inflammatory Responses—A Randomized Clinical Trial. Image Credit: Gulcin Ragiboglu / Shutterstock.com

The health benefits of lentils

The United States Department of Agriculture (USDA) recommends that adults consume about 300 grams of cooked pulses weekly. Lentils, a type of pulse, are known for their high dietary fiber and protein content, as well as the presence of certain bioactive compounds like polyphenols.

To date, few studies have investigated the long-term impact of lentil consumption at the USDA-recommended dose. Moreover, pulse intervention studies have rarely evaluated the gastrointestinal (GI) symptoms that may arise in response to pulse consumption.

About the study

The present randomized clinical trial assessed dynamic lipidemic, glycemic, and inflammation responses during a 12-week dietary intervention of seven midday meals totaling 980 or zero grams of cooked green lentils every week on the health of 18-70-year-olds at a greater risk of developing chronic metabolic disorders.

Included males and females had a waist circumference of 40 or 35 inches or more, respectively, as this is an accepted proxy for central adiposity. Furthermore, all study participants had non-fasting serum triglyceride (TG) levels exceeding 1.69 mmol/L or 150 mg/dL. 

Surveys were administered once a week to assess how lentil consumption impacted GI symptoms and satiety throughout the 12-week intervention. At baseline, anthropometric measurements and each participant’s written consent were obtained.

Habitual dietary patterns and specific diet components were also reported to detect differences between meal groups. At visit two, postprandial serum TG levels were measured to ensure that the study participants continually met the inclusion criteria.

During the 12-week dietary intervention period, study participants were asked to complete a high-fat meal challenge, wherein they consumed a 50-gram oral fat load. Blood samples were collected after fasting and hourly for five hours postprandially for blood marker assessment. 

General linear models were used to assess physical and biological changes across both groups from pre- to post-intervention. Linear mixed-effects models were used to determine the impact of timing and meals on satiety measures and GI symptom severity.

Study findings

A total of 38 overweight and obese adults with a mean age of 47.2 years and body mass index (BMI) of 34.4 kg/m² completed the 12-week intervention. From pre- to post-intervention, anthropometric metrics did not change in either meal group.

Throughout the study period, total fiber consumption averaged 17.3 g and 22.9 g in the lentil and control groups, respectively. While sodium intake increased among lentil consumers, dairy and refined grain consumption decreased among controls.

For lentil recipients, daily average legume consumption significantly increased from baseline at 0.1 to 0.6 cups, which increased their Healthy Eating Index (HEI) scores in four domains. Those who consumed lentils also had higher total, insoluble, and soluble fiber intake.

The mean response rates to the satiety and GI surveys were 89.6 and 90.8% for the control group, respectively, and 89% and 89.4% for the lentil group, respectively. While satiety measures did not vary by meal groups, GI symptom severity responses for both groups were rated as none or mild among 87.7%, with only 10% and 2.3% rating them as moderate or severe, respectively, throughout the 12-week intervention.

Twelve weeks of daily lentil consumption decreased fasting measures of lipid metabolism, including total and low-density lipoprotein (LDL) cholesterol levels. In addition, long-term lentil consumption improved postprandial glucose and inflammation responses to a high-fat meal challenge. 

A potential explanation for this observation is that fiber binds bile acids, thereby preventing their return to the liver and stimulating the production of hepatic bile acids. The body replenishes hepatic cholesterol levels through cholesterol uptake from the blood, which decreases serum cholesterol levels.

Another mechanism by which lentils likely helped reduce serum cholesterol is through saponins, which are bioactive compounds that regulate lipid metabolism and prevent cholesterol absorption. Habitual lentil consumption could also lower total saturated fat intake, a diet component that increases cholesterol levels. 

Conclusions

The study findings indicate that 12 weeks of lentil consumption in individuals at a higher risk of developing metabolic disease could reduce fasting cholesterol levels, as well as improve postprandial glucose and systemic inflammatory responses.  

Lentil consumption exceeding the USDA recommended dose did not cause GI distress. Importantly, these metabolic improvements were independent of changes in anthropometric measures, thus suggesting a direct impact of lentil consumption on metabolism.

Thus, increased lentil consumption could be a safe and effective dietary strategy to improve metabolic health in high-risk populations. Future studies are needed to investigate the impact of prolonged consumption of other pulses on metabolic health.