Here's a new report that links obesity with food allergies. The study found that children who were overweight/obese were significantly more likely to have food allergies, such as allergy to milk. The study doesn't suggest the direction of the causality - is it the food allergies leading to obesity, or is it the other way around?
Based on my previous posts, I believe that a disrupted immune system is at the root of both. It could be that the imbalance of gut bacteria predisposes a person to more food allergies and a higher likelihood of obesity.
In a related study(pdf), overweight people with food allergies were given allergy tests, and then told to avoid these allergic foods for 12 weeks. The result? Subjects lost 37 pounds and 30% body fat. That's a pretty large drop! Control subjects who followed a low-calorie diet while not avoiding allergic foods actually gained fat.
I think it's becoming clearer that obesity is not just about calories.