Any dieticians out there - what are calories?

In answer to the question, I don't think that it matters, but assuming that the calories on the packet are the true version and not some adjusted one, an average person with an average lifestyle needs 2,000 of them per day.

Royal Marine recruits get 4 meals a day so that they can consume the necessary 4,500 calories.

I have found a wide variety of ranges of power output as displayed by exercise machines, but 100 W seems reasonably achievable. So if you manage this for 30 min, you expend 100 x 30 x 60 = 180 kJ = 45 kCal so it is much easier to lose weight by eating less than running more.

If you over eat, you don't keep expanding indefinitely because it takes energy to keep those bigger fat cells alive and to move them around. If you want to lose weight and can bare to get down to 1,000 Cal/day, you should lose 1 kg per week.

Friend of mine at university managed a whole year on a diet of ham sandwiches and best bitter. Unfortunately the bitter/butty ratio increased as the year went on, and he didn't re-appear after the end of year exams.

There was a news article somewhere this week about an American man who was overweight and had tried different diets to no avail. So he decided he wouldn’t give anything up in his diet but instead only eat when he was hungry. He didnt say how much he ate each time but he lost over 100lbs over two years and kept it off. So perhaps rather than count calories or exercise we should all only eat as necessary, difficult I know if you live with someone.

Thanks - my Google-fu is indeed failing it seems. If only they called them Atwater calories I'd have got there! I did know about the factor of 1000 between nutritional and 'physics' calories though. Anyhow, you have answered my question.

The question arose from idle pondering rather than any personal dietary concerns, but reading other responses I do wonder how useful these measures are. I suppose it's just a matter of averages and perhaps extremes. Personally my weight has been pretty stable over the last 50 years without any need to diet or feed up - I just eat what I want when I want. Doesn't work for everyone obviously - metabolism is complicated!

Robin.

One thing that can greatly alter how your body deals with food is the amount of brown fat you have. Some people have a greater ability to dispose of food energy as heat. Typically they are hotter between the shoulder blades. Generally we under use our bodies as machines, look at the amount of energy that navies had to consume to do a days work. We use far less and achieve far less.