Does toasting bread change the amount of calories in the bread? i.e Does a slice of toast have more/less calories that a slice of bread?

I know that some moisture is lost in the toasting process but does the browning of the bread change its characteristics in such a way that it changes the calories?

4 Answers 4


If you are interested in the theory, the answer is yes, there is a change. If you are interested in dieting, the answer is still yes, but it is quite irrelevant to you.

There are two types of browning reactions, Maillard and caramelization. Both start with highly complicated molecules and end with different kinds of highly complicated molecules. For a very precise answer to your question, one would have to know every possible chemical reaction occuring there, the energy trapped in the precursors and in the resulting molecules, and whether this energy is accessible for the human body (e.g. there is quite a lot of energy in raw petrol, but your body can't extract it if you happen to eat it). As these reactions haven't been studied in this level of detail, it isn't possible to give you a really precise answer.

On the other hand, the tendency would be for the calories (at least the digestible ones) to fall somewhat. First, the calories from amino acids and carbohydrates (which are the inputs for browning) are digestible; some of the reaction products can be digestible, but not all will be. Second, some of the calories will literally disappear in thin air - because some of the products of these reactions are volatile.

But if you are expecting to reduce your dietary calorie intake by eating toasted bread, it will probably make no difference at all. First, the calorie-reducing effects will only occur for a small part of the molecules involved. Second, and more important: even if it did occur for all molecules involved, browning only happens on the surface (theoretically, it could happen on the inside too, if you heated it in the 154°C - 190°C range. Practically, if you are doing that, nobody will want to eat that food). The surface is quite small as opposed to the rest - let's assume a slice with 1 cm thickness and a generous browning of 0.5 milimeter depth. (I know that the part which gets hard is thicker, but it doesn't really get browner). I'll disregard the surface enlargment caused by leavened-bubbles in the crumb (because I'm afraid I might end up with an infinite fractal surface :) ) and then we have ~10% of the slice browned. As I said, there is no chance that all the calories in this part disappear completely, and I doubt that the reduction will be really significant. But even if it was at really high 50%, you only get 5% reduction in total, or 10 calories per slice of white bread, less for diet-friendly breads (and this number is just an inflated best-case guess).

  • 1
    This is a really excellent answer
    – nixy
    Apr 19, 2011 at 15:19
  • Great answer! The question was not dieting related at all. Just curiosity. Though I guess even if there was a significant reduction in the calories in the toast, I find that I generally put more butter on toast than on bread because the warm toast melts and absorbs the butter more easily than bread.
    – Catch22
    Apr 20, 2011 at 9:48
  • 2
    @Catch22, try buttering the bread first, toasting second. Same amount of butter as nontoasted bread, tastes much better because the butter browns too. And if you really don't mind the calories, sprincle sugar on the butter before toasting.
    – rumtscho
    Apr 20, 2011 at 11:51

Being a chef. I know that the darker I make my roux the less of a thickening capability it has. Because charcoal cannot absorb moisture. So it would make sense that the more you toast a slice of bread the fewer calories it has. How much less that's up for discussion.

  • 3
    The thickening power of roux is not analogous. What would be is if a dark roux had fewer calories than a light roux, given the same initial ingredients. There certainly is a difference in toast, but it is trivially small.
    – SAJ14SAJ
    Jan 5, 2014 at 14:59

I think theoretical ,that bread will burn off some calories, because of the browning process.However, the molecules, doesn't stand a chance against high heat.The molecules must disappear .

  • 4
    I am sorry, this doesn't make sense. Browning reactions, as in toasting (Maillard and caremlization) are not burning; they are far more complex. Molecules may disappear in that their constituents recombine into new molecules, but how does this help answer the question?
    – SAJ14SAJ
    Jun 24, 2013 at 17:54

I think that by Toasting the bread, you are reducing the calories of the piece of bread, from 110 to 30, my doctor suggests i do it for my personal health and the health of others, the more you toast bread, the more you can eat :D

You know the black on the bread from toast, those are all burned calories.

  • I'll give you the benefit of the doubt and assume you're seriously trying to answer the question, so -1, completely false. As rumtscho already said, there is a difference but it's nowhere near that significant. You and your doctor seem to be a bit misguided. You'd have to have burned 70% of the bread to get a reduction like you're talking about. If you're toasting it in a way that leaves it edible, most of it's unaffected.
    – Cascabel
    Aug 6, 2013 at 21:26

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