Translation:I do not like talking about food but I like food!
In fact, as an Arab, I see your sentence is more accurate in translation for this Arabic sentence than their own English translation. This is because the noun الأكل is more likely associated to "eating" than to "food." Food is usually addressed using طعام (Ta3ám). In dialects and everyday slang, yes we do use "Akl" to mean "food" interchangeably. But this is not quite proper and good Arabic, so to say.
Actually your answer is correct. It's Duolingo's problem.
"Eating" and "food" can be somewhat interchangeable. However, in most contexts, the word for food is طعام (Ta3ám) and not أكل. To be precise, أكل should be the process name (eating) and not the thing which is eaten (food) - Using أكل for food is more colloquial and common in dialects, but speaking linguistically, this is wrong; It shouldn't be like that. So, your answer is correct, but it's Duolingo's problem. They are mixing many dialectical usage with proper Arabic.
Maybe it is one of these cases in English when using the indefinite noun is made for the general sense. Like when you say for example I like nature for a general sense of nature, being plants, insects or whatever. It would somehow feel or sounds weird a bit if you say I like THE nature. Unless you want to add something to "the nature" here like I like THE nature OF something. So my guess is that they didn't add THE for that reason. In Arabic though, as you can see, AL is there anyway.