Once upon a time …
I found this on the forum (some times ago)
Picture original post : Ascension Items for max. Tier
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Hmm… I think I know that last picture. 
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wanna add this here:
from here: How many 1* or 2* feeders does it take to level a 3*, 4*, or 5* hero? - #17 by TaquitoJimmy
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On the basis of the excellent content above, and in context that many of us will have recently gained roster space following the recent soul exchange, I thought to mention some optional tips related to efficient food use when levelling heroes.
The basic process idea is to feed batches of 10 heroes at a time to each recipient. The food cost of feeding heroes goes up with each level gained by the fed hero. However, perhaps due to a history in the game where it used to only be possible to feed heroes 10 at a time, the cost does not increase for the second to tenth hero fed in a batch.
As noted in the OP, 20% extra xp is gained when feeding colour for colour.
As mentioned, the cost of feeding heroes goes up with levels, but the baseline of costs differs for rare, epic, and legendary heroes as follows:
Feeding a single hero (of any type) to a 3 * hero from level 1 (of any of its ascensions) costs 2100 in food.
Feeding a single hero (of any type) to a 4 * hero from level 1 (of any of its ascensions) costs 3000 in food .
Feeding a single hero (of any type) to a 5 * hero from level 1 (of any of its ascensions) costs 5000 in food.
If a lack of food is an issue slowing a players game down then, long term, the fastest way of levelling will be to feed low xp value feeders (1 *s etc.) to lower star type heroes at lower levels, and higher xp value feeder (including trainer heroes) to higher star type heroes at higher levels.
A context in which heroes are devalued over time may alternatively be considered and, in some cases, a priority may be to simply focus on levelling up whichever hero as soon as possible.
At a different extreme, there may be advantages is using the initial teams from a roster for a feeding plan. Here’s the one I currently use:
(c Boldtusk is in the bottom level as a project to return to).
The process cycle is to: increase the number of feeders in a roster either by gaming or pulling from a training camp or hero academy, picking a hero that you think may have 10 feeders in your roster of the colour and quality suited to them, and, if there are 10, go ahead with the feeding.
The food savings are mainly from feeding appropriate xp values of feeders to appropriate targets, but the feeding of heroes 10 at a time can also have relevance, especially at initial levels where ten feeders can get a hero to jump multiple levels.
Assuming a 0.4 cost for levelling costumes, costs for levelling epic and legendary heroes are:
4* total xp to 4/70:
15780+25536+42555+83721
= 167592…
assuming 0.4 xp for a costume:
4* + 1c.: 167592 * 1.4 = 234629…
4* + 2c.: 167592 * 1.8 = 301666…
4* + 3c.: 167592 * 2.2 = 368703…
4* + 4c.: 167592 * 2.6 = 435740…
4* + 5c.: 167592 * 3 = 502776…
5* total xp to 3/70:
26810+48455+104815
= 180080…
5* total xp to 4/80:
26810+48455+104815+173484
= 353564…
assuming 0.4 xp for a costume:
5* + 1c.: 353564 * 1.4 = 494990…
5* + 2c.: 353564 * 1.8 = 636416…
5* + 3c.: 353564 * 2.2 = 777841…
5* + 4c.: 353564 * 2.6 = 919267…
5* + 5c.: 353564 * 3 = 1060692…
So, in sequence, the xp levelling costs are:
4* total to 4/70 = 167592…
(5* total to 3/70 = 180080…)
4* + 1c.: 167592 * 1.4 = 234629…
4* + 2c.: 167592 * 1.8 = 301666…
5* total to 4/80 = 353564…
4* + 3c.: 167592 * 2.2 = 368703…
4* + 4c.: 167592 * 2.6 = 435740…
5* + 1c.: 353564 * 1.4 = 494990…
4* + 5c.: 167592 * 3 = 502776…
5* + 2c.: 353564 * 1.8 = 636416…
5* + 3c.: 353564 * 2.2 = 777841…
5* + 4c.: 353564 * 2.6 = 919267…
5* + 5c.: 353564 * 3 = 1060692…
Levelling a 5* og takes less xp than fully levelling a 4* toon.