Have you been on many medications such as antibiotics in the past? Also you say you drink beer once or twice weekly, how long have you been doing this? The reason i am asking these questions is because both drugs and alcohol can reduce your liver's capability to function at its optimum. The liver is the main organ of fat metabolism, and if your liver is not functioning properly you are not metabolising your fats properly which means you will be storing fat. A sign of poor liver function is fat around the gut. I would highly suggest you see a naturopath who will be able to help you greatly because i know it is very difficult to lose fat around your gut area compared to other places and since this is the main place you want to lose weight u need to treat the cause of the problem as to why you are gaining weight around your middle.
With your diet you need to really increase your protein intake some examples are; salmon, tuna, nuts and seeds (sunflower and pumpkin) lentils, lean chicken. And really decrease your intake of carbohydrates. If you are having carbs stay away from highly refined carbohydrates (white bread, white rice and pasta) since these carbs are just sugar to your body. Instead go for brown rice, multi grain bread etc. Carbs are your bodies first energy source, and if you are eating too many carbohydrates your body will use the carbs that it needs and then store the excess as fat. In a high protein low carbohydrate diet, your body will not have the chance to use the carbs that you are intaking from your diet since there will barely be any and it will start breaking down the stored fat into glucose (sugar) which is your bodies first energy source and you will begin to lose weight.
Max's suggestion with resistance weight training is fantastic you need to do more weight training since muscle burns fat. Stick with cardio but you must include weight training. It will also give you more muscle definition.
I hope i was able to help you