Thermic Effect of Food Calculator

How to use the thermic effect of food calculator

First choose how you want to describe your diet with the Input option:

• Percentages: the share of your energy that comes from carbohydrate, protein and fat, for example 50, 20 and 30.
• Proportions: the same shares written as fractions of one, for example 0.5, 0.2 and 0.3.
• Number of kcal or kJ: the energy each macronutrient supplies, for example 800 kcal of carbohydrate, 400 of protein and 700 of fat. Each amount has its own kcal/kJ menu.

With percentages or proportions the three shares must add up to 100 percent (or 1), apart from a very small rounding gap; otherwise the tool says the macro proportions must sum to about 1.

Two optional boxes extend the result. Total Intake is your daily energy intake and turns the percentage into an energy amount. TDEE is your total daily energy expenditure and adds a comparison with it. When you enter energy amounts instead of shares, the three amounts add up to the intake, so the Total Intake box is hidden and the amount is always shown. The unit you pick beside TDEE decides whether kcal or kJ comes first in the answer.

What the thermic effect of food is

Digesting a meal is work. The body has to break food down, absorb it, move nutrients around and store or burn them, and all of this uses energy. That cost is the thermic effect of food (TEF), also called diet-induced thermogenesis. It shows up as a rise in heat production and oxygen use for several hours after eating.

TEF is one of the three components of daily energy use, alongside resting metabolism and physical activity. In a typical mixed diet it accounts for around a tenth of the energy eaten, which is why many sources say "about 10 percent". The exact figure depends heavily on what you eat, and that is what this calculator estimates.

How the estimate is made

Each macronutrient is assigned a typical thermic effect, a percentage of the energy it supplies that is spent on processing it. The calculator uses the middle of the ranges commonly reported in the research literature:

The thermic effect of the whole diet is the weighted average:

TEF % = carb share × 7.5 + protein share × 25 + fat share × 2.5Shares are fractions of total energy (0.5 for 50%). The result is a percentage of total energy intake.

TEF (kcal) = TEF % ÷ 100 × energy intake (kcal)

To show kJ the calculator multiplies kcal by 4.184. Dividing the TEF amount by your TDEE gives the share of daily expenditure that digestion represents.

Worked examples

Percentages. A 2,000 kcal day made of 50% carbohydrate, 20% protein and 30% fat. Carbohydrate supplies 1,000 kcal and costs 7.5% of that, 75 kcal. Protein supplies 400 kcal at 25%, which is 100 kcal. Fat supplies 600 kcal at 2.5%, which is 15 kcal. The total is 190 kcal a day, or 9.5% of intake (794.96 kJ). If your TDEE is 2,500 kcal, digestion accounts for 190 ÷ 2,500 = 7.6% of it.

Energy amounts. 800 kcal from carbohydrate, 400 from protein and 700 from fat make 1,900 kcal. TEF = 800 × 7.5% + 400 × 25% + 700 × 2.5% = 60 + 100 + 17.5 = 177.5 kcal, which is 177.5 ÷ 1,900 = 9.34% of the energy eaten.

How the macronutrient balance changes TEF

Protein is by far the most expensive macronutrient to process, and fat is the cheapest. The next table compares five diets on a 2,000 kcal day, using the values above.

Moving from the low-protein to the high-protein diet adds about 70 kcal of digestion cost a day. That is real but modest, roughly a small snack. Higher-protein eating can still help with weight control for other reasons, such as greater fullness and better preservation of muscle during weight loss. To plan the split itself, use the macro calculator.

Limits of the estimate

• Fixed percentages. Real TEF varies with meal size, how processed the food is, fibre content, age, body composition and insulin sensitivity. Whole, minimally processed foods tend to cost more to digest than refined ones.
• Alcohol is ignored. It has its own thermic effect, and the shares you enter must cover all your energy.
• TEF is already inside your TDEE. Multiplier-based estimates such as the TDEE calculator include food digestion in the activity factor, so do not add it a second time.
• It is not a loophole. Eating more to burn more does not work: only a fraction of each calorie is spent on digestion, and the rest still counts.

For resting energy use alone, see the BMR calculator, and for a calorie target that combines these pieces use the weight loss calorie calculator.

These figures are general estimates and not medical or nutritional advice. See our disclaimer.