Thermic effect of food
Thermic effect of food, or TEF in shorthand, is the amount of energy expenditure above the resting metabolic rate due to the cost of processing food for use and storage. Simply, it's the energy used in digestion, absorption and distribution of nutrients. It is one of the components of metabolism along with resting metabolic rate and the exercise component. Two other terms commonly used to describe the thermic effect of food are dietary induced thermogenesis (DIT) and specific dynamic action (SDA). 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.
Factors that affect the thermic effect of food
The thermic effect of food is increased by both aerobic training of sufficient duration and intensity and by anaerobic weight training. However, the increase is marginal, amounting to 7-8 Calories per hour. The primary determinants of daily TEF are the quantity and composition of the food ingested.
Although some believe that TEF is reduced in obesity, discrepant results and inconsistent research methods have failed to validate such claims.
Types of foods
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
- Protein: 20 to 35%
- Fats: at most 5 to 15 %
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.
The Functional Food Centre at Oxford Brookes University conducted a study into the effects of chilli 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".
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.
The thermic effect of food should be measured for greater than or equal to five hours.
The American Journal of Clinical Nutrition published that TEF lasts beyond 6 hours for the majority of people.
Processed foods and TEF
Research has found that the thermic effect of food contributes to the fact that calories may not all be equal in terms of weight gain. In one study, seventeen subjects ate, on two different days, two bread-and-cheese sandwiches that were the same in terms of calories (the subjects were free to choose either 600 or 800 kcal meals), but one was ″whole food″ (a multi-grain bread, containing whole sunflower seeds and whole-grain kernels, with cheddar cheese), while the other was ″processed food″ (white bread and a processed cheese product). For each subject, the researchers measured the extra energy, beyond that due to the basal metabolic rate, that the subject expended in the six hours following the consumption of the meal; that energy divided by the energy content of the meal was (after multiplying by 100) reported as the percent DIT coefficient. The average percent DIT coefficient for the ″whole food″ sandwiches was (19.9±2.5)%, while for the ″processed food″ sandwiches, it was (10.7 ±1.7)%—a difference of a factor of 2. When the DIT values are subtracted from the total meal energy, it follows that the subjects obtained 9.7% more net energy from the ″processed-food″ meal than from the ″whole-food″ one.
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