Antonyms for the phrase "are source of" can include terms such as "depleted resources," "lack of," or "absence of." For instance, if someone were to say that healthy soil is a source of rich nutrients, the opposite would be poor soil, which is a depleted resource. Similarly, if we were to say that exercise was a source of energy, the antonym might be a lack of activity, which can lead to feelings of tiredness and lethargy. In essence, antonyms for "are source of" describe the absence or depletion of the essential elements that create a positive outcome.