A number of factors can contribute to the development of obesity. These take effect through a range of different mechanisms but, in all cases, the consequence is the storage of surplus energy as excessive quantities of body fat. Spices such as chilies, garlic and fenugreek can help to check weight gain and reduce obesity.

Fat deposition is a defensive mechanism that enables the storage of energy when food is abundant, thereby increasing the chances of survival during times of food scarcity and famine. In earlier times those individuals who were efficient at storing fat were more likely to survive food shortages. Unfortunately, during times of plenty we retain this innate capacity to store fat and what was once an advantage for the efficient energy accumulators has now become a health risk for them.

Viewed simplistically, obesity is caused by too much energy intake, in the form of food, and not enough energy output, in the form of basic metabolic processes and exercise. However, the reasons that so many of us become overweight or obese are a little more complex than this straightforward equation suggests. Although a sedentary lifestyle and the availability of cheap, high-energy carbohydrate and fat-laden foods are the principal causes of obesity, there are sometimes other aggravating factors. These are diverse and include a genetic predisposition; lifestyle-related factors such as stress and sleep deprivation; psychological problems that manifest themselves as eating disorders; underlying illness; certain medications; a diet dominated by high glycaemic index foods; and habitual dieting with its attendant weight cycling. It has been suggested recently that certain virus infections can increase a tendency to put on weight.

In many cases these factors work by interfering with our appetite control mechanisms, which are partially responsible for the maintenance of normal weight. The failure of appetite (satiety) control is often directly responsible for obesity and can exacerbate and entrench the condition once it has developed. Satiety control mechanisms may also be dampened as a consequence of obesity which has been caused by other factors. A number of mechanisms are involved in this complex regulatory system, and a malfunction of any one of these may result in the consumption of excess food.

The senses of smell and taste are two of the most important of the appetite control mechanisms. When we smell or eat food, receptors in the nose are stimulated by food odor molecules and convey these signals to the satiety centre in the brain. By monitoring the intensity of these signals, the satiety centre is able to gauge when we have had enough to eat. As a result, individuals who have a poor sense of smell or who suffer from a complete loss of the sense of smell tend to eat more than those with a normal sense of smell. Unsurprisingly, strongly flavored and seasoned foods ? which often owe this property to spices ? stimulate the satiety centre far more effectively than bland foods, and we tend to eat less of the former as a result.

Distention of the stomach by food also induces the release of hormones that act as appetite suppressants and some foods, particularly the spices, have the same effects, even in the absence of stomach distention. A group of hormones, one of which is leptin, are produced by fat tissue and are thought to play an important role in appetite regulation.

Spices have a number of properties that make them effective agents to help prevent and treat obesity. In their role as appetite suppressants, spices are known to work in three principal ways.

1. Appetite suppression: The strong odors and flavors common to all spices rapidly stimulate the satiety center in the brain, thereby diminishing feelings of hunger. Certain spices, such as chilies, act by simulating the release of appetite suppressing hormones in the intestine. Garlic meanwhile reduces the appetite by increasing the brain's sensitivity to leptin.

2. Increase metabolic rate: Some spices stimulate the nervous system to release hormones like adrenalin. These hormones speed up the metabolic rate which, in turn, helps "burn off" surplus fat. Capsicums (including chilies and red peppers) and garlic have both been shown to increase the metabolic rate, in some cases by up to 10 percent. Clinical trials have demonstrated that these spices can be effective both in protecting against weight gain and assisting in weight loss. In the capsicum family, more than one phytochemical is known to be responsible for this effect: capsaicin (found in high amounts in chilies) and the less spicy capsiate (found in the milder paprika and red peppers) both increase metabolic rate.

3. Reduce fat absorption: Ginger, fenugreek and garlic all have the ability to reduce the absorption of fat from the intestines.

The diverse ways in which spices act provide the ideal combination of tools to help with the natural treatment of obesity. In conjunction with a sensible weight loss program, they are useful natural treatments for obesity and overweight.