That's mostly wrong. Everyone is predisposed to store excess energy as fat. Cutting back calories doesn't cause a significant increase in metabolic efficiency (unless you're really suffering from starvation which wouldn't apply to anyone on a regular calorie restriction diet). The reason that weight loss tends to slow down for most people on diets is that it simply takes less energy to maintain a lower body mass. So to sustain the same rate of weight loss they would have to keep decreasing calorie intake.
Resting metabolic rate tests are widely available for about $75. You just sit in a chair for a few minutes while a machine measures your exhalations. This is worth doing occasionally if you can afford it to establish an accurate baseline. A lot of people blame their failure to lose weight on a "slow metabolism" which is almost never correct: metabolic rates for individuals with a given height, weight, and sex differ by only a few percent.
Resting metabolic rate tests are widely available for about $75. You just sit in a chair for a few minutes while a machine measures your exhalations. This is worth doing occasionally if you can afford it to establish an accurate baseline. A lot of people blame their failure to lose weight on a "slow metabolism" which is almost never correct: metabolic rates for individuals with a given height, weight, and sex differ by only a few percent.