Thermogenesis

Thermogenesis - heat production in the body is controlled by hormones like Thyroid hormone, Norepinephrine and Leptin. Some food substances (thermogenics) can also stimulate the process of thermogenesis. For example Chilies, Capsicum, Ginger and substances like Ephedra and Caffeine are known to stimulate thermogenesis - and for this reason, they might be used to increase the energy expenditure well above the basal metabolic rate of the body in obese individuals.

Weight Loss by any means is often hard to maintain in most people. The increasing obesity levels in many countries point to many underlying causes:

High Calorie Food
Sedentary Lifestyle
Increased prevalence of mechanical aid in daily routines.

Adaptive Thermogenesis : The collective Behavioral, Metabolic, Neuroendocrine actions may play a role in this Adaptive Thermogenesis - the ability of the body to 'adapt' to negative energy balance. Adaptive thermogenesis reduces the chances of successful body weight loss. This might be in addition to the Homeostasis - the ability of a human body to maintain a stable state of equilibrium under varying impetus. Some people are known to display a very narrow range of weight loss/ weight gain even under exceptional circumstances.