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Fat How it gets made and broken down

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How does fat get made?

We eat to (a) have building materials for our cells, and (b) to get energy for chemical reactions in our cells.

Excess protein or carbohydrates get broken down, and rebuilt as fat molecules, usually triglycerides.

What happens to fat when it is broken down?

Eventually, broken down fat turns into CO2 and H2O. The H2O stays in your body as regular water, and excess water is removed by sweating and urination. The CO2 is removed as you exhale.

When you lose weight, where does it go? Turns out, most of it is exhaled.

Myth: Fat gets burned, and turned into “energy” or heat.

Reality: Fat is made of atoms. Those atoms get broken apart and rearranged into other molecules.

To lose weight, we must break triglycerides into smaller molecules. We need oxygen to do this. Part of this process is oxidation.

Doesn’t happen all in one step.

Some fats get converted to Aceryl-CoA and glycolysis intermediates, but even these will eventually break down int into CO2 and H2O.

When a triglyceride is oxidized the process consumes many molecules of oxygen while producing carbon dioxide (CO2) and water (H2O) as waste products.

So, for example, to burn 10 kilograms (22 lbs.) of fat, a person needs to inhale 29 kg (64 lbs.) of oxygen….
burning that fat will produce 28 kg (62 lbs.) of carbon dioxide and 11 kg (24 lbs.) of water.

“None of this biochemistry is new, but for unknown reasons it seems nobody has thought of performing these calculations before,” study authors Ruben Meerman and Andrew Brown of the University of New South Wales in Australia, said…. during weight loss, 84 percent of the fat that is lost turns into CO2 and leaves the body through the lungs, whereas the remaining 16 percent becomes water, according to the study.

“These results show that the lungs are the primary excretory organ for weight loss. The water formed may be excreted in the urine, feces, sweat, breath, tears or other bodily fluids, and is readily replenished,” the researchers said.

The calculations also show the frightening power of, for example, a small muffin over an hour of exercise: At rest, a person who weighs 154 pounds (70 kg) exhales just 8.9 mg of carbon with each breath. Even after an entire day, if this person only sits, sleeps, and does light activities, he or she exhales about 200 grams of carbon, the researchers calculated.  A 100 g muffin can cover 20 percent of what was lost.

On the other hand, replacing one hour of rest with exercise such as jogging, removes an additional 40 g of carbon from the body, the researchers said. Even if one traces the fates of all the atoms in the body, the secret to weight loss remains the same: In order to lose weight, one needs to either eat less carbon or exercise more to remove extra carbon from the body.

– Exhaled Pounds: How Fat Leaves the Body, Bahar Gholipour, Live Science, 12/14

Reference: When somebody loses weight, where does the fat go?
BMJ 2014; 349 doi: https://doi.org/10.1136/bmj.g7257 (Published 16 December 2014)

Abstract:  When somebody loses weight, where does the fat go?

Considering the soaring overweight and obesity rates and strong interest in this topic, there is surprising ignorance and confusion about the metabolic process of weight loss among the general public and health professionals alike. We encountered widespread misconceptions about how humans lose weight among general practitioners, dietitians, and personal trainers (fig 1⇓). Most people believed that fat is converted to energy or heat, which violates the law of conservation of mass. We suspect this misconception is caused by the “energy in/energy out” mantra and the focus on energy production in university biochemistry courses. Other misconceptions were that the metabolites of fat are excreted in the faeces or converted to muscle. We present a novel calculation to show how we “lose weight.”

Learning standards

Massachusetts Curriculum Frameworks: Biology

8.MS-PS1-1. Develop a model to describe that (a) atoms combine in a multitude of ways to produce pure substances which make up all of the living and nonliving things that we encounter, (b) atoms form molecules and compounds that range in size from two to thousands of atoms, and (c) mixtures are composed of different proportions of pure

HS-LS1-6. Construct an explanation based on evidence that organic molecules are primarily composed of six elements, where carbon, hydrogen, and oxygen atoms may combine with nitrogen, sulfur, and phosphorus to form monomers that can further combine to form large carbon-based macromolecules.
Clarification Statements:
• Monomers include amino acids, mono- and disaccharides, nucleotides, and fatty acids.
• Organic macromolecules include proteins, carbohydrates (polysaccharides), nucleic acids, and lipids.

Disciplinary Core Idea Progression Matrix: PS1.A Structure of matter

That matter is composed of atoms and molecules can be used to explain the properties of substances, diversity of materials, how mixtures will interact, states of matter, phase changes, and conservation of matter.

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