A study published in the NEJM, Oct 2011, revealed that restricting calories and weight loss can increase hormones (such as ghrelin) involved in increasing appetite and decrease hormones (such as leptin) that help you feel satisfied and promote energy expenditure. So there may well be a biological component that affects your desire and efforts to lose weight.

COMMENT: It has long been thought by medical professionals that being overweight results from not dieting and exercising. Many people however, have tried to diet and exercise but could not gain weight and felt it was their "metabolism". Now we know that this may be true. Unfortunately, you may feel like you're fighting a losing battle. However, exercise and diet are important to your health even if you are overweight, so still need to be done. Motivation and trying to overcome your hunger is necessary for maintaining weight loss. Hopefully in the future, leptin-type medications may be produced that can help decrease appetite.