The evidence that tree nut consumption is associated with weight loss runs counter to the theory that increased consumption of fatty foods is associated with weight gain. However, it is difficult to ignore the accumulating research that shows that tree nut consumption is beneficial to correct weight maintenance and does not cause increased adiposity. There is little evidence to suggest that inclusion of high quantities of tree nuts to the diet causes weight gain, and clinical trials that have tested the effects of nuts on weight changes have been consistent in their findings that common varieties of nuts are beneficial to body composition and blood lipid concentrations. For example, one group of researchers1 has investigated the effects of including 53g of salted pistachio nuts as a snack in a weight loss diet, compared to an isocaloric weight loss diet using pretzels as the snack food.
Both groups lost weight in the 12 week study, possibly due to a 500kcal reduction in maintenance calories. Significant improvements in body mass index were seen in the pistachio group when compared to the pretzel group (30.1 to 28.8kg/m2 versus 30.9 to 30.3kg/m2, respectively). The pistachio group also exhibited significantly lower plasma triglyceride levels at 6 weeks and 12 weeks, when compared to the pretzel group (88.0 versus 144.6mg/dL and 88.1 versus 132.2mg/dL, respectively). The consumption of pistachio nuts has been shown to decrease risk of heart attacks in previous studies, although the reason for this is unknown. One explanation is that pistachio nuts have a unique nutrient profile containing high concentrations of unsaturated fatty acids, γ-tocopherol, β-carotene, lutein, selenium, flavonoids and phytooestrogens. In a previous paper the authors of this study characterised the unique anthocyanin content of the pistachio peel.
Nuts are likely beneficial to the heath because they are nutrient dense foods that supply important compounds for correct metabolic function. In this way, they increase the quality of the diet and decrease the risk of serious disease and obesity. Nuts contain a dense source of calories and while it might be assumed that this could lead to weight gain, evidence does not support this viewpoint. Some evidence has suggested that the energy from tree nuts is not fully absorbed, and this is certainly one possible explanation as to why weight gain does not occur. Studies have shown that elimination of refined carbohydrates from the diet and replacement with nutrient dense foods has resulted in weight loss, even if energy content of the food is not restricted. Nuts may therefore be beneficial to weight loss in the absence of a negative energy balance.
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