The basic equation for weight management is rooted in the Newtonian Laws of Thermodynamics: You can't create or destroy energy, you can only change its form. In the nutrition world, this is translated as "calories in = calories out."
Many diet enthusiasts hate this very notion. In fact, some decry that accounting for calories is old fashioned and out of date, that it's carbohydrates or fat that make us fat. "Calories are not all created equal!" they cry. While such a declaration is intended to sound visionary, it plays off an interesting caveat to the generality of the equation: Humans are not walking calorimeters.
It's not groundbreaking to point out that a 2,000-calorie diet of doughnuts is significantly different from a 2,000-calorie balanced diet. Deficiencies matter in living things. Let's face it, calorimeters do not require nutrients; their only job is combustion, which does not result in thinking or movement, growing, exercising or fighting off disease.
This is where research has shown that nuts can make a significant difference. Though peanuts and tree nuts are energy-dense, supplying most of their calories as fat, there are multiple factors justifying the results from epidemiological studies that consuming several ounces of nuts daily can be inversely associated with obesity. Nuts in moderation can contribute to healthy weight management and even weight loss.
Several different mechanisms explain this. The fats and protein content of nuts make them particularly high in satiety value. They reduce overall calorie consumption by allowing one to feel more satisfied with less, and over a longer period of time, compared to consumption of either high-protein or high-carbohydrate diets. Basically, they can discourage overeating.
Nuts are also complex foods rich in fiber and very dense. This might affect energy absorption, limiting it somewhat so that a measurable percentage of the energy is not absorbed. Then there's the thermic effect of food: Consumption of nuts is thought to increase resting energy expenditure, essentially helping you burn calories while at rest.
According to the article "Impact of peanuts and tree nuts on body weight and health weight loss in adults," published in 2008 in the Journal of Nutrition it is estimated that between 55-75 percent of the energy (calories) contributed by nuts to the overall diet is compensated by lower subsequent energy intake.
Most nuts contain substantial amounts of soluble fiber, which tends to slow the movement of food through the digestive tract, while also providing bulk and a satiety-inducing sense of "fullness." As sources of protein and rich in unsaturated fats, the composition of nuts is a combination that can delay stomach emptying. Some nuts have a very dense structure and require a lot of chewing — even the mere act of chewing burns calories, while naturally nutrient-dense foods stimulate a variety of hormones that signal the body to recognize that sense of satiety.
Specifically, cholecystokinin, a hormone synthesized in the cells of the small intestine and secreted in the duodenum, stimulates the release of fat-digesting enzymes from the pancreas and bile from the gallbladder to emulsify dietary fat. This hormone acts as a hunger suppressant, along with ghrelin, a hormone secreted by the stomach, that tells us we've eaten enough.
As mentioned, consumption of nuts is believed to increase the resting metabolic rate, a factor known as the thermic effect of food. The process of chewing is a factor in allowing our digestive enzymes to access the protein, fat, carbohydrates and other nutrients (such as minerals and phytochemicals) from nuts. In "Mastication of almonds: effects of lipid bioaccessibility, appetite, and hormone response," published in 2009 in the American Journal of Clinical Nutrition, the authors demonstrated that the ability to chew nuts is a limiting factor when considering the amount of energy we obtain from the fat.
The calorie value of nuts is only an estimate of potential energy, assuming complete digestion. This means that when eating nuts, more than most foods, a significant amount of energy is lost to the process of digestion than in many foods
Nuts as seeds for the growing plant contain a variety of micronutrients in addition to the protein, fat and carbohydrate, a factor which affects both satiety and overall health. Pistachios, for example, have received attention for their potential to improve blood lipid profiles and reduce the risk of heart disease. But, they are also powerful sources of micronutrients and phytochemicals that can affect inflammation and antioxidant protection.
In a study published earlier this year in Nutrition Reviews, "Pistachio nuts: composition and potential health benefits," pistachios are cited as one of the richest sources of phytochemicals in the nut family. They are the only nut with significant xanthophyll carotenoid content. Another major pistachio carotenoid is lutein, known for potential protection against macular degeneration. Lutein could also help reduce oxidation of small-particle-size LDL, a risk factor for heart disease.
One unique method by which pistachios may aid dieting relates to presentation. Two studies published last year in the journal Appetite, revealed that the visual cues of the empty pistachio shells accumulating on the table help to remind people of their intake, leading to the consumption of fewer calories. Also, the extra time needed to shell the nuts and the extra volume perceived when slowly consuming in-shell pistachios resulted in subjects consuming an amazing 40-percent fewer calories compared to subjects consuming pistachio kernels. The same fullness and satiety was reported.
There are many ways in which fat-rich, calorie-dense nuts in moderation can aid in successful weight management. And there is no need to break laws of thermodynamics — only the laws of fad diets.