Nuts are a nutrient-rich food group. Depending on the type, they may provide substantive concentrations of Vitamin E, magnesium, folate, essential fatty acids, fiber and protein to the diet. They also contain potentially important phytochemicals. By mechanisms yet to be identified, they are reported to improve postprandial lipid profiles and may hold other health benefits. However, they are also energy dense so a theoretical contributor to positive energy balance and weight gain. However, epidemiological studies have consistently revealed an inverse association between the frequency of nut consumption and BMI. Further, intervention trials demonstrate less than predicted weight gain following inclusion of nuts in the diet. The mechanisms for these observations are currently under study. Candidates include strong satiety effects, promotion of energy expenditure and/or inefficient energy utilization. Recent trials have revealed support for each. Inclusion of nuts in the diet results in strong satiety effects as revealed by robust compensatory dietary responses that offset approximately 65-75% of the energy they provide. Several trials note increased energy expenditure that may account for an additional 10% of their energy yield. Limited bioaccessibility results in a loss of 5-15% of energy. Taken together, these findings largely account for the energy provided by nuts and explain the epidemiological and clinical observations. Thus, current knowledge suggests moderate nut consumption does not pose a threat for weight gain.