Chapter 32: Fat loss aids Although there is no magic pill which can cause fat loss without effort, there are supplements which can be combined with dietary changes and exercise to hasten fat loss and/or limit muscle loss. These types of supplements work through a variety of mechanisms including increasing caloric expenditure, preventing a drop in metabolic rate, decreasing the amount of lean body mass lost while dieting and decreasing hunger when calories are being restricted. Fat loss aids can generally be grouped into three categories: thermogenic agents, appetite suppressants, and ‘fat burners’.
Section 1: Thermogenesis and adrenoreceptors Thermogenesis refers generally to the burning of calories to generate heat which is then dissipated by the body. There are numerous types of thermogenesis including exercise-induced thermogenesis and dietary-induced thermogenesis. All forms ultimately cause the body to burn fuel to produce energy and heat. To understand the mechanism by which thermogenic agents work, it is necessary to discuss some of the underlying physiology. This includes a brief discussion of adrenaline and noradrenaline as well as adrenoreceptors.
The catecholamines: adrenaline and noradrenaline In response to stress, the body releases two hormones known generally as catecholamines. They are adrenaline (or epinephrine) and noradrenaline (or norepinephrine). Adrenaline is released from the adrenal glands and travels through the bloodstream to its target tissues while noradrenaline is released only from the nerve endings to act on its target tissues (1). Both work by binding to structures on the cell membrane called adrenoreceptors.
Adrenoreceptors Generally termed, an adrenoreceptor is a specific receptor on a cell which binds to either adrenaline or noradrenaline (1). When binding occurs, the adrenoreceptor sends a signal into the cell causing several reactions to occur. There are two major types of adrenoreceptors: betareceptors and alpha-receptors. As well, there are several subtypes of each receptor. They are discussed briefly below. There are three primary types of beta receptors known as beta-1, beta-2, and beta-3. B-1 receptors are found primarily in the heart and increase heart rate and blood pressure when stimulated. B-2 receptors are found primarily on fat and muscle cells and cause the body to 292