I've been feeling the same way for a while too. What has kicked me into action is health screenings I organised for my work, I thought since I was running it I should set an example and go first. They checked height, weight, cholesterol, blood sugar etc, and give you a health score out of 100. Bearing in mind I'm 25 and not overweight, I scraped in at 37/100, put down to poor diet and smoking too much. I was also told I have a 14% chance of heart problems in the next year - at 25!
So that shocked me into action. I found a great thing for eating healthy though, the supermarkets sell bags of steamed vegetables for a couple of quid, you get about 6 bags in the packet, and you just bang one in the micro for 3mins, and it's a full portion of veg, tastes fantastic too. I've started taking the dogs out more since then also, taking longer walks now the weather's getting better.
Just a couple of changes, and I fell a million times better. Not managed to kick the fags yet, but there's still time!
