If I microwave or heat a potato in a pot, will the amount of calories change due to the heating?

3 responses so far ↓

• 1 mike1942f // Nov 9, 2008

  Very slightly - food calories are actually 1000x heat calories, so if you raise the temp of a potato 100 degrees C and that adds 100 calories per gram temporarily (until it cools) then you have added 10% to the 1000 calories per gram shown in the source (1 food calorie per gram) if you can eat it that hot. http://caloriecount.about.com/calories-potato-baked-flesh-skin-i11674

• 2 Norrie // Nov 9, 2008

  A number of calories (heat units) will be used in raising the temperature of the potato but, the number of Energy Calories will not change.
  A 'calorie' (small 'c') is a unit of heat required to raise the temperature of 1 gram of water by 1°C. (It is equal to 4.184 Joules of heat energy).

  A Food Energy 'Calorie' (note the capital 'C') is equal to the Energy of 1,000 calories. (4,184 Joules).

  The calories added in heating the potato will NOT form a part of the food Calories from the digestion of the potato.

  But, it appears that I'm wrong according to a certain other person. Therefore whatever hot food or drink you take in, you're also increasing your Calorie intake……Even hot water ….Absolute Rubbish.

• 3 m w // Nov 9, 2008

  Mike is absolutely correct. A hot potato adds energy due to it's heat but it's very small compared to the energy produced by metabolizing the potato.

  The energy balance of your body goes something like this.

  energy in + energy produced - energy out = energy accumulated

  When we eat hot or cold foods, heat flows from either our body to the food or from the food to our body (depending on which is hotter) That can be considered "energy in". Metabolism of the food, can be considered "energy produced". Energy out could be in exercise, waste excretion, or heat transfer from our skin to the air for example.

  We usually bake our potatoes at say 450F and butter them at say 200F. We probably eat them at about 150 F. Our core temperature is about 100F so dT is about 50F. Let's say dT = 30C since I'm doing some hand waving here. It doesn't matter much as you'll see in a moment.

  If we assume the heat capacity of a potato is about the same as water, 1 cal / g C and the potato is an 8 oz potato, 227 g the amount of heat transfered from the potato to you by eating it hot is m Cp dT = 227g x 1 cal/gC x 30C = 6810 calories

  next.

  the amount of heat generated by metabolizing the potato is

  278 dietary calories for a 299 g potato (according to Mike's reference). so our 227 g potato would have

  227 g x (278 cal / 299g) = 211 dietary calories.

  but. a dietary calorie is 1 kcal of heat calories

  so the comparible heat calories contained in that potato would be 211,000 calories

  and total calories of potato + heat = 211,000 + 6810 = 217, 810 calories. so the heating of the potato added 3.2% more calories to the potato.

  the actual source of the heat is irrelevant. microwave vs boiling makes no difference.

  ****************
  ok. so does that mean we can lose weight drinking ice water? you betcha. say you drink 1 L of ice water per day. that's 1000 g. at 0C and your body heats it up to 38 C (100 F)

  1000 g x 1 cal / gC x (30-0 C) = 30,000 cal = 30 dietary calories.

  ie you can burn 30 "dietary" calories each day by drinking 1 liter of ice water.

  Of course an order of "chips" with curry sauce and a pint of bitter would probably be about 10x that so depending on what else you consume it may not make much of a difference.
  Mike's point exactly

  *****
  if this is rubbish, so is conservation of mass and energy.