Legumes and Weight Management

It can be challenging to help people adjust their diet to meet their nutrient needs and promote weight loss, while at the same time still keeping them satiated. Nutrient rich legumes can be a valuable part of such a diet. They contain soluble fibre and protein and are mostly low glycemic index (GI), all of which may help promote satiety.

Emerging evidence suggests including three to five cups (1 cup cooked = 150g) of legumes a week in an energy-restricted diet may help improve weight loss. A recent review of the evidence found that of the five trials to investigate the effect of legumes in a calorie–controlled diet, four reported significant reductions in weight between 3.6kg and 8.1kg over six to eight weeks compared to diets without legumes.

For long-term weight management, observational studies suggest a link between dietary patterns incorporating legumes and lower BMI as well as reduced risk of obesity. In a US–based population study of 1,475 adults, regular consumption of beans was associated with lower BMI, 23% reduced risk of increased waist size and 22% reduced risk of obesity compared to those who did not eat beans.

Legumes may assist in short-term weight loss through their effect on satiety for up to four hours. It is suggested this ‘second meal effect’ is the result of higher levels of fibre and resistant starch in legumes which remain undigested until they reach the large bowel where they are fermented. The fermentation products are used for energy in preference to glucose, thus suppressing appetite for longer periods.

Suggested Mechanisms
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 GI 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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