A handful of almonds, hazelnuts, pumpkin seeds, chia seeds or walnuts as a healthy snack or tossed in salad, a smoothie or your breakfast won't make you fat. In fact studies have shown these protein rich, nutritious snacks can actually support weight loss by promoting satiety and blood sugar. Too many bowls of salted nuts, washed down with several beers on the other hand might.
Always choose raw, unsalted, unroasted varieties such as hazelnuts, almonds or walnuts and have them in place of your usual sweet treat, not in addition to. You could also try almond/hazelnut/walnut butters and spread them on oat cakes or rye bread (available from healthfood stores).