I was listening to an interview with Jason Fung recently. According to him, fats can push blood sugar up 8 hours after being consumed. This leads me to conclude that the question of whether or not IF is going to be of benefit to weightloss will depend on a number of variables: e.g. how insulin resistent your body is (or how effective it is at burning dietary carbohydrates, rather than storing them as glycogen); another factor would be your consumption of fat the previous day: a high fat evening meal might lead to an insulin response to breakfast the following morning.

Give that we are all different, and we eat different diets, the only way you can really judge it it might be beneficial to you based on your diet is to do a comparison by eating the same diet for a few weeks, then for the next few weeks eat the same foods, but incorporate an intermittent fasting window by adding the food from breakfast (or dinner) to the other meals, so you're not changing the food or macronutrient balance. You can then compare the results to give you an idea of whether IF might benefit you while eating that particular diet. With a different diet, you might find that the same comparison would produce different results.

If you have very low bodyfat, and are heavily muscled or large framed, then it's possible that you are already at an ideal weight and your body will resist any attempts to lose more.

Just to comment in general, people generally get a bit more insulin resistent as they get older, so we have to be that bit more careful if we want to lose weight.