The quote below came from the Negative Calorie Foods Site:

"All foods have some calories. No food is actually "negative calorie" food. BUT the overall effect of certain foods in our body is that of "negative calories". Negative calorie foods are foods, which use more calories to digest than the calories the foods actually contain!

Calories from these foods are much harder for the body to breakdown and process. In other words, the body has to work harder in order to extract calories from these foods. This gives these foods a tremendous natural fat-burning advantage.

A piece of dessert consisting of 400 calories may require only 150 calories to be digested by our body, resulting in a net gain of 250 calories which is added to our body fat! According to this theory, for example, if you eat 100 calories of a food that requires 150 calories to digest, then you've burnt an additional 50 calories simply by eating that food."
Get instant access to the entire list of Negative Calorie Foods, The Grapefruit Diet and the Popular Cabbage Soup diet in the Negative Calorie Food List Report.

 Negative calorie diet

Reprinted with permission from the
NFPT Personal Trainer Magazine

Is this possible? Can a food actually have not only no calories, but even negative calories? And, if it is possible what effect would ingesting negative calories really have? Could you literally eat your way to fat loss...the more you eat the more you lose?

And, on the down side would the ingestion of “negative calories” potentially offset your “positive calorie” energy reserves, canceling out the effectiveness of your bodybuilding training? Because, as we all know we need calories to manufacture energy both for exercise and for recovering from exercise.

When this subject was first brought to our attention, we immediately dismissed it as not only ludicrous, but impossible as well. We have since done some homework, and determined that in a twisted sort of way, there may actually be some truth to this innovative perspective on the composition of some foods.

 Negative calorie food concept

We already know what you’re thinking, “If there’s really anything to this ‘negative calorie’ food concept, I could get a list of these foods and use them to help me lose weight next spring, or to cut-up for my next show!?” Well, we who are on the NFPT Review newsletter staff are not going to burst your bubble, because in a sense... SURPRISE, you may be right!

All right, we give up, there really is no such thing as negative calorie food. That is to say, not until these particular foods have been ingested. What happens after that however, may come dangerously close to what could ultimately be interpreted as truly a fat loss response on the part of resulting internal metabolic processes.

Before we get ahead of ourselves, consider this. All foods have a caloric (calories), nutrient (carbohydrate, fat, protein), and vitamin & mineral (enzyme producing) content.

For the purpose of this article, we will concern ourselves with the calorie & enzyme producing components of foods. While it is true, enzymes are not found in foods, it has been simplified by researchers, that vitamins can be considered biochemicals found in foods that, among their many other functions, stimulate living tissues to produce enzymes that ideally are sufficient to breakdown that particular food’s caloric nutrients. Therefore, for our purposes the relative result of vitamin ingestion is the production of enzymes.

As a side note, this lay definition of vitamins paves the way for a more clear understanding of empty calories (junk food) as well. Foods falling into this “empty calorie” category would be foods with too little enzyme producing vitamin & mineral content, while containing a surplus of calories.

The ingestion of empty calorie foods requires the body to produce its own enzymes (usually in the lining of the intestinal tract) to be able to convert these “empty calories” into usable energy. Obviously, these enzyme producing functions in the body should be reserved for the performance of other internal, and more vital metabolic reactions.

It is a given these days, that it is difficult to find foods that contain a sufficient amount of vitamins & minerals to alone break down their own “host” caloric nutrients (purely natural food). This situation can be attributed to nutrient robbing pesticide application, processing, the use of preservatives, and various commonly used poor cooking practices.

Surprisingly, in the case of the negative calorie foods in question not only do they contain sufficient vitamins & minerals to break down the host calories there is actually a surplus of these enzyme producing biochemicals. This simply means that once ingested these “negative calories” foods provide for enzyme production in quantities sufficient to break down not only its own host calories, but possibly additional calories present in digestion as well.

Is this discovery truly a tremendous breakthrough? Not really. Unless of course research is performed confirming that these surplus enzymes produced in digestion are in some way transported into the bloodstream. As likely as this enzyme transport would seem, until now there has been no real evidence to support this conclusion.

 Negative calorie research

Reference #1:
According to a recent study performed by Dr. Dean Ornish, M.D., of the University of California, at San Francisco, a vegetarian diet consisting mostly of fruits and vegetables, was adhered to by research subjects as an experimental study on the reversal of heart disease. As a result each of the research subjects (all suffering from heart disease), lost an average of 20 pounds without cutting calories or limiting serving sizes.

In light of the fact that these subjects were 40 years and older (with relatively slowed metabolisms) and the research performed involved no prescribed exercise program, this constitutes a dramatic weight loss that could only be attributed to the consumption of various fruits & vegetables.

Reference #2:
In an article in the January, ’94 Issue of Self Magazine, contributed by Dr. Neal Barnard M.D., author of “Food For Life” (Harmony Books), he basically supports the concept of “negative calories” foods (keep in mind there were no research studies referenced in this article to support his claims).

Let’s speculate for a moment, shall we? With the above information in mind, while obviously not conclusive, let us assume the transport of these “surplus digestive enzymes” into the blood is a given and pick it up from there. The fact is, enzymes are responsible for the acceleration of ALL chemical reactions in the body. The acceleration of chemical reactions in the body then equates to a faster metabolism (this effect is implied by the earlier referenced studies performed by Dr. Dean Ornish, M.D.).

If CONCLUSIVE this discovery would truly be a tremendous breakthrough. The greater value then, in identifying and ingesting these negative calorie foods is not in their ability to break down other existing calories in digestion at all.

The true potential benefits lie in the increased enzymes produced being absorbed through the mucosa in the small intestine thus entering into the bloodstream where they can positively effect the rate of metabolism.

In building upon the above conjectures, to optimize this metabolic acceleration, these researched & identified negative calories should preferably be ingested in the absence of additional enzyme robbing “empty calories” (junk food). This would insure that an optimum amount of enzymes are produced for absorption into the bloodstream and not wasted during digestive processes on assimilating calories from foods with poor vitamin and nutrient content.

The article above came from the NFPT Personal Trainer Magazine Over 12 Years of Personal Trainer Certification, Credibility & Support. The Most Trusted Name in Personal Fitness Trainer Certification Internationally.