BACKGROUND: Dietary guidance issued by various global government agencies recommends nut consumption within the context of a healthy-eating pattern. Nuts are nutrient dense and may promote nutrient adequacy. As an energy-dense food, nuts must replace other foods in the diet to prevent an excess of calories. METHODS: We evaluated how recommending the inclusion of walnuts (75 g day(-1) ) in the diet affected energy and nutrient intake in men (45-75 years; mean body mass index = 27.6 kg m(-2) ; n = 19) at risk for developing prostate cancer. Guidance was provided about incorporating walnuts isocalorically in a healthy diet. Three-day food records and body weight were collected at baseline and after two 8-week diet periods (usual versus walnut supplement diets). RESULTS: Energy intake on the walnut supplement diet exceeded the usual diet, although body weight was maintained. Energy intake was lower on the actual walnut supplement diet than the calculated walnut diet [10,865 kJ (2595 kcal) versus 11,325 kJ (2705 kcal) per day, respectively] and contributed 23% less energy than 75 g of walnuts. Approximately, 86% and 85% of the total fat and saturated fatty acids from walnuts were not displaced, whereas the increase in fibre from the usual diet to the actual walnut supplement diet represented less than one-half (39%) of the fibre provided by 75 g of walnuts. Walnuts were substituted, in part, for other foods, and the nutrient profile of the diet was improved, however, the beneficial effect of walnuts on the diet quality was not optimized. CONCLUSIONS: Individuals do not optimally implement food-based guidance. Consequently, nutrition professionals play a key role in teaching the implementation of food-based recommendations.