Is It True That Fiber Has Negative Calories?

This question is very similar to the question about celery taking more energy to chew than it provides in kilocalories.
There are two different types of fiber; the soluble type like the fiber found in oatmeal and insoluble type as is found in celery. Both are technically carbohydrates which mean they should have 4 kcal/gram. But, since the body is unable to fully digest fiber, researchers have suggested that a value of 2 kcal/gram be used to calculate their caloric value. This recommendation is based on what is called a "mixed" diet which means that along with the fiber you are also eating other carbohydrates, fats, and proteins.
FYI: The nutrition information on celery indicates that 1 cup contains almost 4 grams of fiber and has 19 calories. This discrepancy indicates a gap in research and practice because according to Guenther and Jensen, this cup of celery should contain only 8 calories.

Source: Guenther, P.M. & Jensen, H.H. (2000).Estimating energy contributed by fiber using a general factor of 2 vs 4 kcal/g. Journal of the American Dietetic Association. 100(8).

The brain and the heart are essential organs for life, but does one require more energy than the other? GUEST BLOG

Today's guest blog is written by Mandi

The brain cells need two times more energy than any other cell in the human body. The cells that communicate with each other, neurons, have a high demand for energy because they are always in a state of activity. Even while we are sleeping, neurons are at work fixing and rebuilding components. They manufacture enzymes and neurotransmitters that have to be sent out to the nerve branches. Bioelectric signals responsible for communication throughout the nervous system demand the most energy from neurons. This action alone accounts for half of all the brain's energy. The heart, however, only requires the same amount of energy as other muscle organs.

Source: http://www.fi.edu/learn/brain/carbs.html