The obesity problem is growing, even though we have more "diets" available to us today than ever before.
Firstly, most conventional "diets" dramatically reduce calorie intake. This in itself can send your body into starvation mode and store fat instead of burn it. If your body thinks food is scarce, it will slow down your metabolism to keep you from starving. This is one of the many wonderful natural survival mechanisms our bodies come with.
We would have greater success working with our body's natural metabolism functions, not against them. We need to eat food to increase our metabolism and lose weight. Eating more and more often keeps the survival mechanism of storing fat from kicking in. Your body assumes you can get all of the food you need and STOPS storing fat. This speeds up your metabolism, naturally.
Secondly, the foods you choose can spike your insulin level. The diets that have low carbohydrates have had short-term success because simple carbohydrates turn to a kind of sugar very quickly in your blood stream and cause a spike in your insulin level. Staying away form them will help you lose weight quickly, but can harm how your body functions. Your body needs some carbohydrates, your brains sole source of glucose comes from them. Simple carbohydrates include things that taste sweet like sugar, candy, honey and sweet fruits.
Processed carbohydrates like refined bread and pasta are the worst. They have been stripped of all the fibre that slowed down the conversion to sugar. If you are going to eat bread or pasta, choose whole grains. If losing weight is your goal, stick to complex carbohydrates.
Thirdly, one diet can't work for everyone. We all have a different body type and chemistry. Knowing which body type you are and eating the foods that work with it is a huge key to long-term weight loss.

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