Specific dynamic action

Specific dynamic action (SDA), also known as thermic effect of food (TEF) or dietary induced thermogenesis (DIT), is the amount of energy expenditure above the basal metabolic rate due to the cost of processing food for use and storage.^[1] Heat production by brown adipose tissue which is activated after consumption of a meal is an additional component of dietary induced thermogenesis.^[2] The thermic effect of food is one of the components of metabolism along with resting metabolic rate and the exercise component. A commonly used estimate of the thermic effect of food is about 10% of one's caloric intake, though the effect varies substantially for different food components. For example, dietary fat is very easy to process and has very little thermic effect, while protein is hard to process and has a much larger thermic effect.^[3]

The thermic effect of food is increased by both aerobic training of sufficient duration and intensity or by anaerobic weight training. However, the increase is marginal, amounting to 7-8 calories per hour.^[1] The primary determinants of daily TEF are the total caloric content of the meals and the macronutrient composition of the meals ingested. Meal frequency has little to no effect on TEF; assuming total calorie intake for the days are equivalent.

Some studies suggest that TEF may be reduced in patients with obesity, although research findings are mixed.^[4] A low TEF could potentially predispose to obesity by reducing energy expenditure and promoting a positive energy balance. Alternatively, the presence of a low TEF in many patients with obesity may be explained by insulin resistance, which can be related to excess dietary energy and vary in severity with the degree of obesity. Over time, chronic hyperinsulinemia could diminish the ability of cells to respond to insulin, promote adiposity and peripheral insulin resistance, and worsen the risk for type 2 diabetes. Some research shows that TEF may be more severely impaired in patients depending on the grade of insulin resistance, although some other studies have not reproduced that finding.^[5]

The mechanism of TEF is unknown, although it may be related in part to increases in sympathetic activity induced by eating food.^[6]: 505 TEF has been described as the energy used in the distribution of nutrients and metabolic processes in the liver,^[7] but a hepatectomized animal shows no signs of TEF and intravenous injection of amino acids results in an effect equal to that of oral ingestion of the same amino acids.^[6]: 505

The thermic effect of food is the energy required for digestion, absorption, and disposal of ingested nutrients. Its magnitude depends on the composition of the food consumed:

• Carbohydrates: 5 to 15% of the energy consumed^[8]
• Protein: 20 to 30%^[8]
• Fats: at most 5 to 15%^[9]

Raw celery and grapefruit are often claimed to have negative caloric balance (requiring more energy to digest than recovered from the food), presumably because the thermic effect is greater than the caloric content due to the high fibre matrix that must be unraveled to access their carbohydrates. However, there has been no research carried out to test this hypothesis and a significant amount of the thermic effect depends on the insulin sensitivity of the individual, with more insulin-sensitive individuals having a significant effect while individuals with increasing resistance have negligible to zero effects.^[10][11]

The Functional Food Centre at Oxford Brookes University conducted a study into the effects of chilli peppers and medium-chain triglycerides (MCT) on Diet Induced Thermogenesis (DIT). They concluded that "adding chilli and MCT to meals increases DIT by over 50% which over time may accumulate to help induce weight loss and prevent weight gain or regain".^[12]

Australia's Human Nutrition conducted a study on the effect of meal content in lean women's diets on the thermic effect of food and found that the inclusion of an ingredient containing increased soluble fibre and amylose did not reduce spontaneous food intake but rather was associated with higher subsequent energy intakes despite its reduced glycaemic and insulinemic effects.^[13]

The thermic effect of food should be measured for a period of time greater than or equal to five hours.^[14]

The American Journal of Clinical Nutrition published that TEF lasts beyond six hours for the majority of people.^[14]

• Glickman, N; Mitchell, HH (Jul 10, 1948). "The total specific dynamic action of high-protein and high-carbohydrate diets on human subjects" (PDF). The Journal of Nutrition. 36 (1): 41–57. doi:10.1093/jn/36.1.41. PMID 18868796.