Remember when you were growing up, you could eat whatever the hell you wanted?

Every school day you gobbled down chocolate and gulped down pop and you stayed lean as a whippet. But now if you so much as look at a plate of chips, you bloat like a pufferfish. There's a reason for that. When your parents told you that one day your metabolism would slow down, they weren't joking. When you reach a certain age your body's calorie needs peak and after that, you need less and fewer calories to maintain weight, according to UCLA statistician Nathan Yau. That's not necessarily a problem if you're eating less and less food at the same time. But if you're still eating like a horse - powering through bottles of cola, snacking on doughnuts and still eating three huge meals a day - then the law of calories in/calories out dictates that you will put weight on. The graph, from the US Department of Health, below shows how much less food you should be eating ever years as you age and was published on Yau's Flowing Data blog Women who are active (doing more than three miles a day) see their calorie need peaks in their teens at 2,400 calories. Women doing moderate activity (so one to three miles a day) can quite happily maintain their body weight on 2,200 daily calories from their mid-teens to their mid-twenties. But that metabolism starts slowing when you hit 25 by around 200 calories. For women who are sedentary (no daily exercise and lots of TV and sitting at a desk) peak in their late teens to mid-twenties when their metabolism starts slowing and their body only needs around 2,000 calories. It keeps on dropping with age. This gives you a very clear idea of when you need to start curbing the booze and takeaway binges. Interestingly the grey bars on the graph show women's actual food consumption - and what you'll notice is active people aren't eating enough, while sedentary women are eating way too much.