A baked potato: 368 kJ per 100 g. The same potato as crisps: 2,140. Nearly six times the energy, and the potato didn't change. What we did to it did.
Same food. Different number.
Most of the energy in a food comes down to two things: how much water it holds, and how much fat it carries. Change either one and the kilojoules can jump dramatically, even though it's still "just a potato" or "just fruit".
We compared 12 everyday foods with their dried, fried or concentrated versions, gram for gram, using the Australian Food Composition Database.
Take water out. Or put fat in.
Take the water out
Water has no energy, so removing it concentrates everything left behind: sugars, fibre and minerals alike. That's why a sun-dried tomato or a sultana is so much denser than the fresh version, with nothing added at all.
Put the fat in
Fat holds 37 kJ per gram, more than double protein or carbohydrate. Frying, roasting in oil or skimming off cream loads it in. A potato soaks up oil as a crisp; milk becomes cream by concentrating its fat.
Often, it's both. Banana chips lose their water and gain oil and sugar, which is how a banana ends up with more energy per gram than potato crisps.
Twelve foods, before and after.
Sorted by how much the energy jumps. Every bar is drawn on the same scale, from 0 to 3,695 kJ (olive oil), so you can compare across cards.
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Tomato → Sun-dried tomato
15×Fresh73 kJSun-dried1,101 kJNo oil added. Drying takes the tomato from 94% water to 25%, so everything else is concentrated, including fibre and potassium.
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Cranberries → Dried cranberries
10×Fresh131 kJDried, sweetened1,330 kJMost of the sugar in dried cranberries is added: about 68 g per 100 g. Fresh cranberries are very tart, so they're usually sweetened before drying.
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Apricots → Dried apricots
5.9×Fresh166 kJDried972 kJWater drops from 87% to 26%. Gram for gram, dried apricots carry about 4.5 times the fibre of fresh ones.
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Potato → Potato crisps
5.8×Baked, no fat368 kJCrisps2,140 kJFat goes from zero to 33 g per 100 g, and salt from almost none to 592 mg of sodium.
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Figs → Dried figs
5.5×Fresh195 kJDried1,082 kJDried figs bring 200 mg of calcium and 14 g of fibre per 100 g.
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Banana → Banana chips
5.4×Fresh399 kJBanana chips2,171 kJUsually deep-fried and sweetened. Fat rises from 0.2 g to 34 g per 100 g.
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Milk → Thickened cream
5.3×Regular milk270 kJThickened cream1,422 kJCream is the fat skimmed off the top: about 36 g of fat per 100 g, against 3.4 g in milk.
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Grapes → Sultanas
4.7×Green grapes277 kJSultanas1,308 kJA 30 g handful of sultanas has the energy of about 140 g of grapes.
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Apple → Dried apple
4.5×Fresh242 kJDried1,078 kJDrying takes the apple from 83% water to 21%. The fibre stays, and comes along more densely.
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Olives → Olive oil
4.3×Olives868 kJOlive oil3,695 kJOlives are two-thirds water. The oil is pure fat, and the most energy-dense food on the list.
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Plums → Prunes
4.1×Fresh plum209 kJPrune865 kJPrunes keep the fibre: about 7.7 g per 100 g, nearly four times a fresh plum.
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Rice → Rice crackers
2.5×Boiled rice659 kJRice crackers1,626 kJBoiled rice is over 60% water. Puff and dry it into crackers and the energy more than doubles.
Energy per 100 g. Grey is the starting food, blue is the dried, fried or concentrated version.
The humble potato, three ways.
Same vegetable, three very different numbers. Baked with no fat, a potato is one of the lightest foods in your kitchen. Deep-fried as takeaway chips, it more than doubles. As crisps, it lands next to nuts and chocolate.
Baked
0 g fat, 7 mg sodium and 576 mg potassium per 100 g.
Crisps
33 g fat and 592 mg sodium per 100 g. A small 25 g bag has about the energy of 145 g of baked potato.
Takeaway chips: deep-fried in blended oil, regular cut. Values range from about 940 to 1,020 kJ depending on the oil.
What equal kilojoules look like.
Gram for gram is only half the story, because nobody eats 100 g of sun-dried tomatoes. Here's how much of each version gives you the same energy.
- 30 g of sultanas = 140 g of grapes. A small handful vs a big bunch.
- 30 g of dried apricots = 175 g of fresh apricots.
- A 25 g bag of crisps = 145 g of baked potato.
- 1 tablespoon of olive oil = 60 g of olives.
Calculated from energy per 100 g and rounded.
Dense isn't the same as bad.
Drying concentrates the good along with the energy. Per 100 g, dried apricots have about 4.5 times the fibre and more than 5 times the potassium of fresh ones. Dried figs bring 200 mg of calcium, and prunes nearly 8 g of fibre.
The difference is the extras. Plain dried apricots, sultanas, figs, prunes and apple have no added sugar, but dried cranberries and banana chips do, and crisps add oil and salt. So check the label, and let the portion do the work: a small handful of dried fruit, not the whole bag.
Four easy wins.
When you want to feel full, fresh fruit and baked or boiled potatoes give you more food for the same energy.
Small appetite? A handful of dried apricots, figs or prunes packs energy, fibre and minerals into a few bites.
Check the ingredients on dried cranberries, banana chips and fruit mixes. Plain dried apricots, sultanas and prunes usually have none.
A baked potato with a little olive oil still comes in far below takeaway chips or crisps.
A lot in. Not much you don't want.
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Sources and notes
All figures are per 100 g from the Australian Food Composition Database (Release 3), using generic Australian foods: for example, pale-skin potato baked without fat, plain salted potato crisps, raw green grapes, regular-fat milk and thickened cream. Brand products vary.
This article is general information only and is not a substitute for advice from your doctor or dietitian. Always read the label. Follow directions for use. Vitamin and mineral supplements should not replace a balanced diet.
