Text
Chris should eat less chips to lose weight for the bike race in two months.
Assumption
Eating chips is the main reason Chris isn't losing weight right now.
Answer
It doesn't need to be assumed that eating chips are the main reason Chris doesn't lose weight. There may be other requirements to make Chris lose weight, if he also eats a lot of sweets, for example. This is not unrealistic and the text can then be true without making the assumption.