In the 1880's, Wilbur Atwater used a 'bomb calorimeter' to calculate the change in heat in a closed container in order to measure the energy contained in different foods. The theory was, if you eat fewer calories than your body burned up, you would lose weight.
This formed the basis of the western worlds obsession with cutting calories. We do know that cutting back does cause weight-loss, but that it is unhealthy (see my previous post). The theory does work, but sadly it's not as simple as it sounds. The trouble is, when you cut your calorie below the amount you actually need your metabolism slows down so you burn up less energy. Makes sense doesn't it, you eat less than you need, so your body goes into a conservation or starve mode. Now that specifically isn't a problem, well it isn't if you know what signs of metabolic damage to look out for. If one wants to work on a deficit it makes sense that at first sign of metabolic damage (cold hands and feet, lowered libido, fertility problems, hypoglycaemia, hormonal issues etc) you would cease the diet and repair your metabolism. It isn't the diet that always causes the problem, but the amount of time someone tries to engage in it or the high percentage deficit they attempt. Its the biggest thing I struggle with in my work, it seems so simple yet people really do always fall back into the "must burn more calories and eat less" mantra. The mechanism is there to help us survive starvation so we can't beat the system.
My research shows that 1800 calories is technically semi starvation. Remember this figure and lower is often mentioned as healthy by diet clubs and I frequently consult with people eating far lower. In the year 2000, leaders of rich and poor countries set a target to end extreme poverty worldwide by 2015 by means of eight Millennium Development Goals.
The first goal is: Eradicate extreme poverty and hunger.
The benchmark for hunger is an average intake of 2,100 kilocalories a day, which is slightly higher than the recommended allowance for women in the UK. Absolute madness yet they go on to state that, "people who have less than this suffer symptoms of malnutrition, including impaired ability to learn or work, and reduced resistance to disease. So hunger is a cause as well as a consequence of poverty. "Even the Scientific Advisory Committee on Nutrition think that our calorie recommendations are low, yet we continue to aim for a low calorie lifestyle.