Some Carbs Turn to Fat Fast in Your Body
According to new research, people on low-carb diets lose weight in part because they get less fructose, a type of sugar that can be made into body fat quickly.

The study shows that the type of carbs someone eats can be as important as the amount. Although fructose is naturally found in high levels in fruit, it is also added to many processed foods, especially in the form of high-fructose corn syrup.

For the study, six healthy people performed three different tests involving drinking various mixes of glucose and fructose. Researchers found that fructose turned into body fat much more quickly, and that having it for breakfast changed how the body handled fats at lunch.
Sources:
NBC5 July 25, 2008
Journal of Nutrition June 2008, 138:1039-1046

Dr Levin's comment (8/19/08):
this makes perfect sense to me.  Based on my clinical experience, people consuming products with high fructose corn syrup seem to have quite a bit of trouble losing weight; even when they consume relatively low calorie diets.  Instead, increase your exercise, both cardio and weight resistance training, and reduce your carbohydrate intake.  Be especially careful of
simple carbohydrates (bagels, muffins, pasta, cakes, cookies, candy, soft drinks etc...).  If you have more than 50lbs to lose, consider a very low carb diet to start off for about a month and then reintroduce healthy carbs such as fruits and berries.  Whole grains, such as whole grain bread and pasta can be added back as well; however if you have a weight problem, these foods
can cause a significant insulin response which will make it harder to continue to lose weight. 

I have also found that having a goal, such as running a 5K or hiking a certain trail, or playing tennis again can be very helpful.  When we have a goal to shoot for we tend
to be more motivated.  Good luck and much success.

In health,
Neil Levin DC