Lentils (Lens culinaris) have been enjoyed by humans for many thousands of years, having been first domesticated in the Fertile Crescent of the Middle East. Nowadays, they are available in many varieties, depending on where you live, and can be classified according to their size (small, medium or large), colour (red, green, yellow, brown, black, etc…), and whether they have been shelled or split.
Like most legumes, they are nutrition powerhouses, with just half a cup (about 93 g or 3¼ oz) of cooked lentils (from dried) providing about 420 kilojoules (100 calories), 7 g protein, 0g fat, 15 g carbs (0.5 g sugars and 14.5 g starches), 2 g fibre, 1 mg sodium, 177 mg potassium and having a low GI (26).
A recently published randomised controlled trial investigated the effect of consuming 0 g (0 oz), 300 g (10.5 oz, equivalent to ~¼ Cup cooked each day), or 600 g (21 oz, equivalent to ~½ Cup cooked each day) of medium green lentils per week for a total of 8 weeks. Thirty middle-aged (average age 41.6 years) overweight or obese American women and men where randomised into one of three groups and provided with pre-prepared midday meals each week, varying the amount of lentils, according to the group.
To ensure they were both nutritious and delicious, the meals were prepared by a registered dietitian and trained professional chef and included soup, curry with basmati rice, street tacos, loaf with mashed potatoes and cooked zucchini, and pasta with Bolognese sauce. Other than the midday meals, participants were asked to maintain their normal dietary and physical activity patterns.
The Homeostatic Model of Insulin Resistance method was used to measure insulin resistance in the liver of all participants. Insulin resistance increased in the control group (those consuming no lentils at midday) by 1.2 units but decreased in a dose-dependent manner in the moderate group, consuming 300 g of lentils per week (–0.9 units) and in the high group, consuming 600 g of lentils per week (–1.5 units).
Importantly, most participants (87.4%) reported either no or only mild gastro-intestinal symptoms after consuming the lentil-based midday meals. Of those that did experience mild symptoms, flatulence was the most common form, with, as you’d expect, high consumers experiencing more bloating, abdominal discomfort, and cramping compared to medium or no-consumers.
While not everyone will want to consume lentils everyday, they are nutritionally very similar to other kinds of legumes like beans and peas, which are also good sources of plant protein, low GI starches and fibre. Enjoying a serve of legumes (½ Cup cooked) each day is an easy addition to the daily diet of people with insulin resistance.
- Wilson and colleagues. Eight weeks of lentil consumption attenuates insulin resistance progression without increased gastrointestinal symptom severity: A randomized clinical trial. Nutr Res. 2022
Dr Alan Barclay, PhD, is a consultant dietitian and chef with a particular interest in carbohydrates and diabetes. He is author of Reversing Diabetes (Murdoch Books), and co-author of 40 scientific publications, The Good Carbs Cookbook (Murdoch Books), Managing Type 2 Diabetes (Hachette Australia) and The Ultimate Guide to Sugars and Sweeteners (The Experiment Publishing).