Below is an excerpt from 天声人語 Jun. 14 2010:
東京大の宮崎徹教授らが、体脂肪を减らすたんぱく質を見つけたという。脂肪を作る働きを抑え、ため込んだ分を使わせる効果があるそうだ。
I wondered for quite some time why 使わせる instead of 使う is used here. Then I speculate that it is an omission of the agent, or the second (二格) object:
[人に]ため込んだ分を使わせる
But I'm not sure. I searched Reverso Context and found this similar example:
全ての物資をラ・ベルから運ばねばならず、体力を使わせる仕事は7月半ばに終了した。
I guess it's
[私に]体力を使わせる
But I am still no more confident about that.
And a further question, if I am right in devising this "agent" theory. I accept that, it is because a laborious (that is, labor-consuming, 体力を使う) task consumes your
strength that you
is involved. But it seems unclear to me how a fat-reducing protein can involve the person using this protein when it takes effect (that is, draining excess body fat, ため込んだ分を使う).
If there's a biological reason for that I think I'm just unlucky.