A review in 2008 concluded that there was insufficient evidence to make any clear conclusions about the effect of legumes on weight control, but other studies suggest there is a possibility of a protective effect.
A cross-sectional study of adults in Iran reported that the risk of being centrally obese was significantly lower in the highest quartile of legume intake in men (30g a day).
A small trial with overweight diabetic subjects in Mexico compared a low-GI and a high-GI diet, with more carbohydrates being provided from legumes in the low-GI diet. Those consuming more legumes had improved glycemic control and greater weight loss.
In an 18-month randomised controlled study carried out in New Zealand with 113 overweight (BMI >28kg/m2) volunteers, an intervention group consumed 2 serves of pulses and 4 serves of wholegrain foods per day as substitutions for more refined carbohydrates. Mean weight loss at 6 months was not different between the intervention and control groups, however, waist circumference was decreased at 18 months in the intervention compared with the control group (-2.8 cm; 95% confidence interval [CI]: -0.4, -5.1) (p > 0.05).
The main postulated mechanism by which legumes may benefit weight management is through their higher fibre content. Legumes, as a source of fibre and resistant starch, may delay gastric emptying and induce in an earlier sense of fullness during a meal. The gastric and intestinal bulking effects of fibre can also promote satiety and in turn reduce energy intakes. Fibre and resistant starch may also delay the absorption of nutrients such as glucose, and possibly fat, thereby increasing insulin sensitivity, decreasing postprandial glycemia and influencing the secretion of gut hormones controlling fat oxidation and storage.
The low GI value of legumes, known to enhance satiety, may be another important mechanism. An Australian study found consuming four 300g cans of chickpeas a week resulted in significantly higher levels of satiety and improved bowel function. A second Australian study, using lupin flour enriched bread at two meals a day, also found higher self-reported satiety and lower energy intakes with the higher legume diet.
There are also indications from research that a legume-rich, low glycemic index diet may reduce circulating leptin concentrations, even under conditions of weight maintenance. Leptin is a hormone that communicates with the central nervous system to regulate energy intake and energy stores in the body. In most overweight people, leptin levels are excessively high due to leptin resistance, a process similar to the concept of insulin resistance, so reducing circulating leptin concentrations in the body is desirable.
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