This is one of the newest and most exciting areas in the study of weight control. Thermogenesis is heat production not accounted for by resting metabolic rate or physical activity. Factors
stimulating thermogenesis include food intake, thermogenic substances (i.e., adrenaline, thermogenic drugs and some types of food), cold exposure and psychological stress.
Thermogenesis accounts for approximately 15% of your daily energy expenditure. Abnormalities in thermogenesis may contribute to obesity.
Thermic Effect Of Food
Unlikely as it seems, eating actually speeds your metabolism. Metabolism increases during digestion, absorption, processing and storing food. Metabolism also increases for several hours after a
meal. The metabolic effects of food intake account for 5-19% of the total energy expenditure. The energy cost of meals is highest for protein, lower for carbohydrates and lowest for fats.
The metabolic response to food is less in obese people. Exercising before a meal increases the thermic effect of food in both obese and lean subject. Exercising after a meal increases the metabolic
cost of food only in lean subjects.
The significance of diet-induced thermogenesis is controversial. Severe dieting reduces metabolic rate, partially because the thermic effect of food is less. Eating 3-6 meals a day during a
weight-loss program may help dieters take advantage of the increasing metabolic rate that accompanies eating. Some researchers feel increases in metabolic rate are trivial, and people should
emphasize caloric restriction.
Facultative thermogenesis is heat production that does not result from mechanical work or synthesis of tissue or stored fuels. Examples include increased activity of brown fat and metabolic
pathways that don't contribute usable energy to the body. These processes decrease metabolic efficiency - you consume calories, but your body doesn't get anything from the energy it has burned.
Brown adipose tissue (BAT) is an important center for thermogenesis in several animal species, including human infants. BAT may be an important center for facultative thermogenesis in adult humans.
However, adults have only a small amount of the tissue. Some researchers have speculated that 40-50 grams of active BAT cold increase metabolic rate 20-25%.
The calorie-burning properties of BAT stem from the ability of its cells to generate heat without using the energy to store fat. If you have a lot of BAT, you will produce more heat and store less
Previously, the small amount of BAT in adult humans led experts to believe that this tissue was not very important at a cause of obesity or leanness. Studies using thermography, a technique used to
measure hot spots in your body, and direct tissue temperature readings following administration of drugs that increase metabolism (e.g., adrenaline) suggest that BAT may play a far more important
role in thermogenesis than previously suspected. Obese people show a much lower heat response to infusion of drugs that stimulate metabolism. This may mean that obese people have less BAT or that the
heat pathway in BAT is less active than in lean people.
Cold exposure, diet, starvation and certain drugs influence BAT activity. Cold exposure, as demonstrated in Korean pearl divers, Finnish workers and military recruits, causes brown fat to increase in
size. While controversial, some studies suggest that exercising in the cold may speed fat loss. Muscle & Fitness carried an article several years ago discussing the merits of regular, brief
periods of exposure to cold water for increasing metabolism and reducing body-fat.
Possible dietary stimulants of BAT include a high-carbohydrate diet, supplements of essential fatty acids (i.e., cis-linoleic acid or cis-gammalinonelic acid) and chromium. Ephedrine, a drug found
naturally in some plants, may also stimulate BAT activity.
* BBR does not recommend using drugs without the advice
and supervision of a physician